Scientific Report of the 2015 Dietary Guidelines Advisory Committee

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Part D. Chapter 2: Dietary Patterns, Foods and Nutrients, and Health Outcomes - Continued

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Dietary Patterns and Body Weight

Question 2: What is the relationship between dietary patterns and measures of body weight or obesity?

Source of evidence: Existing reports

Conclusion

The DGAC concurs with the 2013 AHA/ACC/TOS Guideline for the Management of Overweight and Obesity that strong evidence demonstrates that, preferably as part of a comprehensive lifestyle intervention carried out by multidisciplinary teams of professionals or nutrition professionals, overweight and obese adults can achieve weight loss through a variety of dietary patterns that achieve an energy deficit. Clinically meaningful weight losses that were achieved ranged from 4 to 12 kg at 6-month follow-up. Thereafter, slow weight regain is observed, with total weight loss at 1 year of 4 to 10 kg and at 2 years of 3 to 4 kg. However, some dietary patterns may be more beneficial in the long-term for cardiometabolic health. DGAC Grade: Strong

The DGAC concurs with the NEL Dietary Patterns Systematic Review Project that moderate evidence indicates dietary patterns that are higher in vegetables, fruits, and whole grains; include seafood and legumes; are moderate in dairy products (particularly low and non-fat dairy) and alcohol; lower in meats (including red and processed meats), and low in sugar-sweetened foods and beverages, and refined grains are associated with favorable outcomes related to healthy body weight (including lower BMI, waist circumference, or percent body fat) or risk of obesity. Components of the dietary patterns associated with these favorable outcomes include higher intakes of unsaturated fats and lower intakes of saturated fats, cholesterol, and sodium. DGAC Grade: Moderate

Evidence for children is limited, but studies in the NEL Dietary Patterns Systematic Review Project and the systematic review focused on this age group by Ambrosini et al.34 suggest that dietary patterns in childhood or adolescence that are higher in energy-dense and low-fiber foods, such as sweets, refined grains, and processed meats, as well as sugar-sweetened beverages, whole milk, fried potatoes, certain fats and oils, and fast foods increase the risk of obesity later on in life. DGAC Grade: Limited

Implications

To achieve and maintain a healthy body weight, individuals are encouraged to consume dietary patterns that are higher in vegetables, fruits, and whole grains; include seafood and legumes; are moderate in dairy products (with an emphasis on low- and non-fat dairy), and alcohol; and are lower in meats (including red and processed meats), sugar-sweetened foods and beverages, and refined grains. During childhood and adolescence, a time period critical for the prevention of obesity later in life, a dietary pattern similar to that associated with a healthy weight in adults should be encouraged.

Among overweight and obese individuals, an energy deficit is necessary to achieve weight loss. This can be achieved through a variety of evidence-based dietary patterns and should be approached with comprehensive lifestyle interventions. While it is possible to lose weight on his/her own, it is more successful if conducted by trained professionals or by referral to a nutrition professional for individual or group counseling (for more details refer to AHA/ACC/TOS Guideline for the Management of Overweight and Obesity13 algorithm Box 11B). Strategies should be based on the individual’s preferences and health status and consider the socio-cultural influences on lifestyle behaviors that relate to long-term behavior maintenance. These approaches are best complemented with population-based approaches, as mentioned in Part D. Chapter 3: Individual Diet and Physical Activity Behavior Change and Part D. Chapter 4: Food Environment and Settings, which will allow all factors influencing lifestyle behaviors to be addressed as defined in the socio-ecological model.

Review of the Evidence

The DGAC considered evidence from the 2013 AHA/ACC/TOS Obesity Guideline and associated NHLBI Obesity Report, which included only randomized trials,12 13 the NEL Dietary Patterns Systematic Review Project,2 which included 38 studies predominately of prospective cohort design and a few randomized trials, and two systematic reviews/meta-analyses published since 2008.34 35 In total, 81 articles were considered in these reports. The published reviews provided evidence for the pediatric population (included 7 studies of which 2 overlapped with those in the NEL review) and further evidence for dietary patterns related to the Mediterranean-style diet and its effect on obesity and weight loss (all randomized trials of which 1 out of the 16 studies overlapped with the NEL review).

Dietary Patterns and the Management of Overweight and Obesity

In the NHLBI Obesity Report, the 12 randomized studies described in summary Table 3.1 of the report all confirm that to lose weight, a variety of dietary pattern approaches can be used and a reduction in caloric intake is required. The energy balance equation requires that for weight loss, one must consume less energy than one expends or expend more energy than one consumes. The report states that any one of the following methods can be used to reduce food and calorie intake: prescription of 1,200 to 1,500 kcal/day for women and 1,500 to 1,800 kcal/day for men (kcal levels are usually adjusted for the individual’s body weight); prescription of a 500 kcal/day or 750 kcal/day energy deficit; or prescription of an evidence-based diet that restricts certain food types (such as high-carbohydrate foods, low-fiber foods, or high-fat foods) in order to create an energy deficit by reduced food intake.

For the different dietary approaches (provided either as part of a comprehensive lifestyle change intervention carried out by a multi-disciplinary team of trained professionals or within nutrition interventions conducted by nutrition professionals) that the authors of the report evaluated, it is evident that all prescribed diets that achieved an energy deficit were associated with weight loss. There was no apparent superiority of one approach when behavioral components were balanced in the treatment arms. Results indicated that average weight loss is maximal at 6 months with smaller losses maintained for up to 2 years, while treatment and follow-up taper. Weight loss achieved by dietary techniques aimed at reducing daily energy intake ranges from 4 to 12 kg at 6-month follow-up. Thereafter, slow weight regain is observed, with total weight loss at 1 year of 4 to 10 kg and at 2 years of 3 to 4 kg. The following dietary approaches are associated with weight loss if reduction in dietary energy intake is achieved:

  • A diet from the European Association for the Study of Diabetes Guidelines, which focuses on targeting food groups, rather than formal prescribed energy restriction while still achieving an energy deficit.
  • Higher protein (25 percent of total calories from protein, 30 percent of total calories from fat, 45 percent of total calories from carbohydrate) with provision of foods that realized energy deficit.
  • Higher protein Zone™-type diet (5 meals/day, each with 40 percent of total calories from carbohydrate, 30 percent of total calories from protein, 30 percent of total calories from fat) without formal prescribed energy restriction but realized energy deficit.
  • Lacto-ovo-vegetarian-style diet with prescribed energy restriction.
  • Low-calorie diet with prescribed energy restriction.
  • Low-carbohydrate (initially less than 20 g/day carbohydrate) diet without formal prescribed energy restriction but realized energy deficit.
  • Low-fat (10 percent to 25 percent of total calories from fat) vegan-style diet without formal prescribed energy restriction but realized energy deficit.
  • Low-fat (20 percent of total calories from fat) diet without formal prescribed energy restriction but realized energy deficit.
  • Low-glycemic load diet, either with formal prescribed energy restriction or without formal prescribed energy restriction but with realized energy deficit.
  • Lower fat (≤30 percent fat), high dairy (4 servings/day) diets with or without increased fiber and/or low-glycemic index/load foods (low-glycemic load) with prescribed energy restriction.
  • Macronutrient-targeted diets (15 percent or 25 percent of total calories from protein; 20 percent or 40 percent of total calories from fat; 35 percent, 45 percent, 55 percent, or 65 percent of total calories from carbohydrate) with prescribed energy restriction.
  • Mediterranean-style diet with prescribed energy restriction.
  • Moderate protein (12 percent of total calories from protein, 58 percent of total calories from carbohydrate, 30 percent of total calories from fat) with provision of foods that realized energy deficit.
  • Provision of high-glycemic load or low-glycemic load meals with prescribed energy restriction.
  • The AHA-style Step 1 diet (with prescribed energy restriction of 1,500 to 1,800 kcal/day, <30 percent of total calories from fat, <10 percent of total calories from saturated fat).

Although these dietary patterns with an energy deficit will result in weight loss during a 6-months to 2-year period, long-term health implications with certain patterns may be detrimental to cardiometabolic health. These associations have been discussed in the dietary patterns and cardiovascular health section as well as the saturated fat and cardiovascular health section.

As presented in Table D2.1 at the end of the chapter, the results of the randomized studies considered in the AHA/ACC/TOS Guideline provide evidence for what works in terms of the components of a comprehensive lifestyle intervention or nutrition interventions that are needed to achieve weight loss with the variety of dietary approaches described above.

Dietary Patterns and their Association with Body Weight

A total of 14 studies met the inclusion criteria for the index/score question of the NEL systematic review and were categorized based on dietary pattern exposure. Two major categories were identified: (1) studies that examined exposure based on a Mediterranean-designated dietary pattern and (2) studies that examined exposure based on expert dietary guidelines recommendations. Taken together, there were six studies on Mediterranean-designated diet scores,23 31 32 36-38 five studies on dietary guidelines-based indices,39-43 two studies on Mediterranean-designated scores and dietary guidelines indices,44 45 and one study that used a trial-based customized score.46 Two of the studies were RCTs of positive quality23 46 and 12 were prospective cohort studies. The studies were carried out between 2006 and 2012.

The sample sizes for prospective cohort studies ranged from 732 to 373,803 participants, with follow-up times from 1.5 to 20 years. Ten out of 12 of the prospective cohort studies were conducted with generally healthy adults with a mean age of 25 to 63 years. Two studies were conducted with children and adolescents (one with girls).39 40 The two RCTs were conducted in adults with elevated chronic disease risk: one study with a Mediterranean-designated diet intervention on older adults at increased CVD risk with more than 90 percent overweight or obese23 and one study using an a priori diet intervention on men with pre-existing metabolic syndrome.46 The sample sizes for the RCTs were from 187 to 769 subjects and duration of follow-up ranged from 3 to 12 months.

Mediterranean-style Dietary Pattern

Four out of the six studies evaluating the Mediterranean style dietary pattern were conducted in Spain.23 32 36 37 Of the other two, one study was the European multicenter study that was part of the EPIC-Physical Activity, Nutrition, Alcohol Consumption, Cessation of Smoking, Eating out of Home, and Obesity (EPIC-PANACEA) study,38 and one was conducted in the United States.31 

Dietary Patterns and Body Weight and Incidence of Overweight and/or Obesity

The Prevencion con Dieta Mediterranean (PREDIMED) study tested the effects of a Mediterranean diet on the primary prevention of cardiovascular disease in a high-risk group of men and women. Subjects either had type 2 diabetes or three cardiovascular disease risk factors (such as hypertension or current smoking) and 90 percent were overweight or obese defined as BMI ≥25 kg/m2. The PREDIMED trial randomly assigned participants to three interventions: (1) Mediterranean diet with extra virgin olive oil, (2) Mediterranean diet with mixed nuts, and (3) low-fat diet. At end of 3 months of a 4-year clinical trial, the authors found that the Mediterranean diet score increased in the two Mediterranean diet groups of the trial and remained unchanged in the low-fat group. However, no significant changes in body weight and adiposity occurred within or between groups from baseline to the 3 months. Beunza et al., 2010 reported on a prospective cohort study in Spain, the Seguimiento Universidad de Navarra (SUN) study.36 Participants with the highest adherence to a Mediterranean dietary pattern, assessed using the Trichopoulou Mediterranean Diet Score (MDS) were found to have lower average yearly weight gain, -0.059 kg/y (95% CI = -0.111 to -0.008 kg/y; p for trend = 0.02), than participants in the lowest adherence group.7 However, the MDS was not associated with incidence of overweight or obesity in participants who were normal weight at baseline. Mendez et al., 2006 reported on the EPIC-Spain prospective cohort study.37 Adherence to a Mediterranean diet was assessed using a slight modification of the Trichopoulou MDS, with exposure categorized in tertiles of low (0-3), medium (4-5), and high (6-8) adherence. Participants with highest MDS adherence had reduced incidence of obesity when overweight at baseline; overweight women and men were 27 percent and 29 percent, respectively, less likely to become obese. High MDS adherence was not associated with incidence of overweight in subjects who were normal weight at baseline. The EPIC-PANACEA study examined the association between adherence to the relative Mediterranean dietary pattern (rMDS), prospective weight change, and the incidence of overweight or obesity. Participants with high rMED adherence gained less weight in 5 years than did participants with low rMED adherence (-0.16 kg; 95% CI = -0.24 to -0.07 kg) and had a 10 percent lower odds of becoming overweight or obese (OR = 0.90; 95% CI = 0.82 to 0.96). The contribution of each rMED scoring component also was assessed and it was found that the association between rMED and weight change was no longer significant when meat and meat products were not part of the score. Lastly, a meta-analysis of the odds ratio scores of all 10 European countries showed that a 2-point increase in rMED score was associated with 3 percent (95% CI = 1 to 5%) lower odds of becoming overweight or obese over 5 years.

Dietary Patterns and Waist Circumference

Rumawas et al., 2009 conducted a prospective cohort study using a subset of the Framingham Offspring and Spouse (FOS) study.31 Dietary exposure was assessed in quintiles of low to high adherence to the Mediterranean style dietary pattern score (MSDPS). Participants with a higher MSDPS had significantly lower waist circumference (p for trend < 0.001). Tortosa et al., 2007 reported on the association of the Mediterranean dietary pattern and metabolic syndrome in the SUN study conducted in Spain.32 Participants in the highest tertile of adherence to the MDS had lower waist circumference, -0.05 cm over 6 years (p for trend = 0.038), compared to the lowest tertile.

Although some mixed results from prospective studies may be due to differences in the length of follow up, definition of the Mediterranean dietary pattern and population included, the results of randomized studies indicate a significant reduction in body weight when calories are restricted. A high quality meta-analysis (AMSTAR rating of 11) on the association of a Mediterranean-style diet with body weight conducted by Esposito included 16 randomized studies of which one32 overlapped with the NEL systematic review was included in the DGAC body of evidence for this question. The meta-analysis included studies conducted in the United States, Italy, Spain, France, Israel, Greece, Germany, and the Netherlands that lasted from 4 weeks to 24 months with a total of 3,436 participants. Using a random effects model, participants in the Mediterranean diet group had significant weight loss (mean difference between Mediterranean diet and control diet, -1.75 kg; 95% CI = -2.86 to -0.64) and reduction in BMI (mean difference, -0.57 kg/m2; 95% CI = 0.93 to 0.21 kg/m2) compared to those in the control arm. The effect of Mediterranean diet on body weight was greater in association with energy restriction (mean difference, -3.88 kg; 95% CI = -6.54 to -1.21 kg), increased physical activity (-4.01 kg; 95% CI = -5.79 to -2.23 kg), and follow up longer than 6 months (-2.69 kg; 95% CI = -3.99 to -1.38 kg). Across all 16 studies, the Mediterranean style dietary pattern did not cause weight gain.

Dietary Guidelines-Based Indices

Of the seven studies conducted on dietary guidelines-based indices, three studies were conducted in the United States with U.S.-based indices.39 41 43 One study was conducted in Germany with an index developed in the United States,40 and two studies were conducted in France (one used a French index,42 and the other compared six different dietary scores).44 

Dietary Patterns and Body Weight and Incidence of Overweight and/or Obesity

Gao et al., 2008 reported on a prospective cohort study of White, African American, Hispanic, and Chinese men and women in the Multi-Ethnic Study of Atherosclerosis (MESA) in the US. Two versions of the 2005 HEI were used: the original and a modified version that adjusted the food group components to incorporate levels of caloric need based on sex, age, and activity level.41 For the overall population, there was an inverse association between quintiles of each HEI score and BMI (p<0.001). The risk of obesity in normal weight participants was inversely associated with HEI scores only for Whites (p<0.05). A comparison of the HEI-1995 and HEI-2005 scores indicated that beta-coefficients, as predictors of body weight and BMI, were higher for the HEI-2005 scores in Whites. Zamora et al., 2010 analyzed data from the prospective cohort study, Coronary Artery Risk Development in Young Adults (CARDIA), conducted in the United States, to examine the association between diets consistent with the 2005 Dietary Guidelines and subsequent weight gain in Black and White young adults.43 The Diet Quality Index (DQI) included 10 components of the 2005 Dietary Guidelines relating to the consumption of total fat, saturated fat, cholesterol, added sugars, reduced-fat milk, fruit, vegetables, whole grains, nutrient-dense foods, and limited sodium and alcohol intake. They found, a 10-point increase in DQI score was associated with a 10 percent lower risk of gaining 10 kg in normal-weight Whites. However, the same magnitude increase in score was associated with a 15 percent higher risk in obese Blacks (p<0.001). Kesse-Guyot et al., 2009 conducted a prospective cohort study in France to examine the association between adherence to a dietary score based on the French 2001 nutritional guidelines (Programme National Nutrition Sante´ guidelines score (PNNS-GS) and changes in body weight, body fat distribution, and obesity risk.42 The PNNS-GS includes 12 nutritional components: fruit and vegetables, starchy foods, whole grains, dairy products, meat, seafood, added fat, vegetable fat, sweets, water and soda, alcohol, and salt. The last PNNS-GS component is physical activity. In fully adjusted models, an increase of one PNNS-GS unit was associated with lower weight gain (p=0.004), and lower BMI gain (p=0.002). An increase of 1 PNNS-GS unit was associated with a lower probability of becoming overweight (including obese) (OR = 0.93; 95% CI = 0.88 to 0.99). Similarly, an increase of 1 PNNS-GS unit was associated with a lower probability of becoming obese (OR = 0.89; 95% CI = 0.80 to 0.99).

Two studies were conducted in children. Cheng et al., 2010 analyzed data from a prospective cohort study conducted in Germany, the Dortmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study, to examine whether the diet quality of healthy children before puberty was associated with body composition at onset of puberty.40 Adherence to a diet pattern was assessed by the Revised Children’s Diet Quality Index (RC-DQI) which was based on the Dietary Guidelines for Americans. In this study, a higher dietary quality was associated with a higher energy intake, and children with a lower diet quality had lower BMI and Fat Mass Index (FMI) Z-scores at baseline (p<0.01) but not at onset of puberty. Berz et al., 2011 reported on a prospective cohort study to assess the effects of the DASH eating pattern on BMI in adolescent females over a 10-year period.39 Only seven out of the 10 original components of the DASH score were used; the three excluded were added sugars, discretionary fats and oils, and alcohol. Overall, girls in the highest vs. lowest quintile of DASH score had an adjusted mean BMI of 24.4 vs. 26.3 kg/m2 (p<0.05).

Dietary Patterns and Waist Circumference

Gao et al, found, for the overall population in the MESA study, an inverse association between quintiles of each HEI score and waist circumference (WC) (p<0.001).41 The study by Kesse-Guyot conducted in France showed, in fully adjusted models, an increase of one PNNS-GS unit was associated with lower waist circumference gain (p=0.01) and lower waist-to-hip ratio gain (p=0.02).42 

Other Indices

Jacobs et al., 2009 conducted an RCT in Norway, the Oslo Diet and Exercise Study, to examine the effect of changes in diet patterns on body weight and other outcomes among men who met the criteria for the metabolic syndrome (n=187 men).46 Study participants were randomly assigned to: (1) the diet protocol, (2) the exercise protocol, (3) the diet + exercise protocol, or (4) the control protocol. The trial duration was 12 months. The authors created their own diet score to assess adherence to the intervention. The score was based on summing the participants ranking of intake (across tertiles) of 35 food groups that, based on the literature, had a beneficial neutral or detrimental effect on health. A higher score reflected greater adherence to the diet intervention. Over the course of the intervention, the diet score increased by 2 points (SD ±5.5) in both diet groups, with a decrease of an equivalent amount in the exercise and control groups. A 10-point change in the diet score during the intervention period was associated with a 3.5 kg decrease in weight, a 2.8 cm decrease in waist circumference and 1.3 percent decrease in percent body fat (all significant at p<0.0001).

Studies that Compared Various Dietary Indices

In a study by Lassale et al., subjects were participants in the SUpplementation en VItamines et Minereaux AntioXydants (SU.VI.MAX) study and diet quality was assessed using a Mediterranean Score (MDS, rMED, MSDPS), the Diet Quality Index-International (DQI-I), the 2005 Dietary Guidelines for Americans Adherence Index (DGAI), and the French Programme National Nutrition Sante-Guidelines Score (PNNS-GS).44 Overall, better adherence to a Mediterranean diet (except for the MSDPS) or expert dietary guidelines was associated with lower weight gain in men who were normal weight at baseline (p for trend = <0.05). In addition, among the 1,569 non-obese men at baseline, the odds of becoming obese associated with one standard deviation increase in dietary score ranged from OR = 0.63 (95% CI = 0.51 to 0.78) for the DGAI to OR = 0.72 (95% CI = 0.59 to 0.88) for the MDS, only the MSDPS was non-significant. In women, no association between diet scores and weight gain or incidence of obesity was found. Woo et al., 2008 reported on a prospective cohort study in Hong Kong to examine adherence to a diet pattern using the MDS and the Diet Quality Index International (DQI-I).45 They found that increased adherence to either the MDS or DQI-I was not associated with becoming overweight.

Dietary Patterns from Data-Driven Methods

In the NEL review, a total of 11 studies from prospective cohort studies were included that either used factor or cluster analyses to derive dietary patterns. Eight of the eleven studies were conducted in the United States, with additional studies from the United Kingdom, Iran, and Sweden. The sample sizes ranged from 206 to 51,670 participants with follow-up times from 3 to 20 years. The majority of the studies were conducted with generally healthy adult men and women,47-52 five studies included women only,53-57 and one was conducted in children to examine weight gain in adolescence over the period of follow-up.56 Outcomes examined included change in body weight (3 studies), BMI (7 studies), and waist circumference (6 studies); one study examined both percent body fat and incidence of overweight/obesity.

Most of the studies found at least two generic food patterns: a “healthy/prudent” food pattern and an “unhealthy/western” pattern. Generally, healthy patterns were associated with more favorable body weight outcomes, while the opposite was seen for unhealthy patterns. However, not all studies reported significant associations. There was a potential difference in associations found by sex: of the three studies that analyzed men and women separately, men tended to have null results. However, data were insufficient to draw conclusions about population subgroups. Furthermore, because the patterns are data-driven, they represent what was consumed by the study population, and thus it is difficult to compare across the disparate patterns. The one study that analyzed the dietary patterns of pre-pubescent children transitioning into adolescence showed that patterns vary widely at this age and caution should be observed when analyzing these data because the diet of children changes rapidly, as does their weight.

The DGAC considered the systematic review by Ambrosini et al. that included seven articles, two of which overlapped with the NEL review.34 Results demonstrated a positive association between a dietary pattern high in energy-dense, high fat, and low fiber foods and later obesity (4 of the 7 studies), while three studies demonstrated null associations. The seven longitudinal studies of children from the United Kingdom, United States, Australia, Norway, Finland, and Colombia had follow-up periods ranging from 2 to 21 years and had sample sizes from 427 to 6772 individuals. The studies determined dietary patterns using factor or cluster analysis (5) or reduced rank regression (2).

For additional details on this body of evidence, visit: References 2, 13, 34, 35 and Appendix E-2.27

Dietary Patterns and Type 2 Diabetes

Question 3: What is the relationship between dietary patterns and risk of type 2 diabetes?

Source of evidence: Existing reports

Conclusion

Moderate evidence indicates that healthy dietary patterns higher in vegetables, fruits, and whole grains and lower in red and processed meats, high-fat dairy products, refined grains, and sweets/sugar-sweetened beverages reduce the risk of developing type 2 diabetes. DGAC Grade: Moderate

Evidence is lacking for the pediatric population.

Implications

To reduce the risk of developing type 2 diabetes, individuals are encouraged to consume dietary patterns that are rich in vegetables, fruits, and whole grains and lower in red and processed meats, high-fat dairy, refined grains, and sweets/sugar-sweetened beverages in addition to maintaining a healthy body weight. Diabetes can be prevented through the consumption of a variety of healthy dietary patterns that share these components and that are tailored to the biological needs and socio-cultural preferences of the individual and carried out preferably through counseling by a nutrition professional.

Review of the Evidence

The Committee considered two sources of evidence. The primary source was the NEL Dietary Patterns Systematic Review Project which included 37 studies predominantly of prospective cohorts design and some randomized trials (n=8).2 This primary source was supplemented by a published meta-analysis58 that included 15 cohort studies of which 13 overlapped with the NEL review.58 The meta-analysis provided an estimate of the effect size of incident type 2 diabetes associated with a healthy and unhealthy dietary pattern.

Although the NEL rated the overall body of evidence for type 2 diabetes as limited, this was primarily a result of examining the different methods for defining dietary patterns (e.g. indices, data driven, and reduce rank regression) separately. As such, the NEL noted these methodological inconsistencies across studies but stated general support for the consumption of a dietary pattern rich in vegetables and fruits and low in high-fat dairy and meats. The DGAC concurred with this conclusion. However, the DGAC has elevated the grade of the entire body of evidence to moderate given that the NEL findings were corroborated by the results of a high quality meta-analysis (AMSTAR rating of 11) and the magnitude of the associations that showed when the results of 15 cohort studies are pooled, evidence indicated a 21 percent reduction in the risk of developing type 2 diabetes associated with dietary patterns characterized by high consumption of whole grains, vegetables, and fruit. Conversely, a 44 percent increased risk of developing type 2 diabetes was seen with an unhealthy dietary pattern characterized by higher consumption of red or processed meats, high-fat dairy, refined grains, and sweets.

Dietary Patterns and Incident Type 2 Diabetes

Dietary Approaches to Stop Hypertension (DASH)

One study used the DASH score in a cohort of 820 U.S. adults ages 40 to 69 years and with equal sex distribution and racial diversity.59 Liese et al. found adherence to the DASH score was associated with markedly reduced odds of type 2 diabetes in Whites but not in the total population, or in the Blacks and Hispanics, which comprised the majority of this cohort.

Mediterranean-style Dietary Patterns

Three studies assessed Mediterranean-style dietary pattern adherence (Mediterranean Diet Score [MDS]) with sample sizes ranging from 5,000 to more than 20,000 in both Mediterranean and U.S. populations. One study conducted in Spain with the SUN cohort (n=13,380) found a favorable association between the MDS (the original MDS of Trichopoulou) and risk of type 2 diabetes. Overall, a 2-point increase in MDS was associated with a 35 percent reduction in risk of type 2 diabetes.60 Another study, conducted in Greece with the EPIC-Greece cohort (n=22,295), also assessed the relationship between the MDS and type 2 diabetes. In this second Mediterranean population, adherence to the MDS also was favorably associated with decreased risk of diabetes.61 Conversely, a study conducted in the United States, using the authors’ MedDiet Score with the Multi-Ethnic Study of Atherosclerosis (MESA) cohort (n=5,390) found no association between their MedDiet Score and type 2 diabetes incidence in the total population, in men or women, or in specific racial/ethnic groups.62 

Dietary Indices based on the Dietary Guidelines

Four studies used dietary guidelines-based indices such as the AHEI and the Diet Quality Index (DQI). The sample sizes of the studies ranged from 1,821 to 80,029. A study that assessed adherence to the AHEI in the United States found a favorable association between AHEI score and risk of incident type 2 diabetes in women in the Nurses’ Health Study (n=80,029).63 In the CARDIA study (n=4,381), also from the United States, the authors found no association between DQI-2005 score and type 2 diabetes incidence in the total population or in Blacks or Whites.29 Studies from outside the United States included one conducted in Australia using a Total Diet score in the Blue Mountains Eye Study (BMES, n=1,821) and one from Germany using a German Food Pyramid Index with the EPIC-Potsdam cohort (n=23,531). Neither found an association between these scores and incident type 2 diabetes.64 65 Thus, evidence for an association only exists with the AHEI, which does contain slightly different components from the other indices, such as nuts and legumes, trans fat, EPA + DHA (n–3 FAs), PUFAs, alcohol, red and processed meat.

Data-Driven Approaches

Eleven studies used factor analysis and one study used cluster analysis. These analyses were all conducted using data from prospective cohort studies published between 2004 and 2012 and had sample sizes ranging from 690 to more than 75,000 individuals. Five studies were conducted in the United States and the rest from developed countries around the world. Each study identified one to four dietary patterns, with the most common comparison between "western"/"unhealthy" and "prudent"/"healthier" patterns; a total of 35 diverse dietary patterns were identified within the body of evidence. Many studies had null findings, particularly studies with duration of less than 7 years of follow up.66-69 Patterns associated with lower risk of type 2 diabetes were characterized by higher intakes of vegetables, fruits, low-fat dairy products, and whole grains, and those associated with increased risk were characterized by higher intakes of red meat, sugar-sweetened foods and drinks, French fries, refined grains, and high-fat dairy products. However, the food groups identified varied substantially, even among patterns with the same name.

Three prospective cohort studies used reduced rank regression to examine the relationship between dietary patterns and type 2 diabetes.70-72 Two of the studies were conducted in the United States and one in the United Kingdom. The sample sizes were 880 for Liese (2009), 2,879 for Imamura (2009), and 6,699 for McNaughton (2008). The independent variables in these studies were dietary pattern scores, and biomarkers were used as response variables in two of the studies. Dietary patterns that included meat intake and incident type 2 diabetes were positively associated in the two studies that used biomarkers as response variables, though the definitions of meat differed.70 71 However, because so few studies were available and the methodology used and different populations considered varied so much, the information was insufficient to assess consistency or draw conclusions.

Other Dietary Patterns

The body of evidence examined included seven studies conducted between 2004 and 2013, consisting of six RCTs73-79 and one prospective cohort study (PCS).80 Two studies were conducted in the United States; one in the United States and Canada; one in Spain (2 PREDIMED articles); and one each in Greece, Italy, and Sweden. The sample sizes of the RCTs ranged from 82 to 1,224 participants and the PCS had a sample size of 41,387 participants. All eight studies were conducted in adults. RCT duration ranged from 6 weeks to a median of 4 years and the PCS duration was 2 years. The RCTs were primary prevention studies of at-risk participants. Baseline health status in the study participants included those with mild hypercholesterolemia, overweight or obesity, metabolic syndrome, abdominal obesity, and three or more CVD risk factors, including metabolic syndrome. The PCS participants were individuals in the Adventist Health Study who did not have type 2 diabetes.80 Three studies looked at a Mediterranean-style diet,75 77-79 one study examined the Nordic diet (defined by the authors of the study as a diet rich in high-fiber plant foods, fruits, berries, vegetables, whole grains, rapeseed oil, nuts, fish and low-fat milk products, but low in salt, added sugars, and saturated fats),73 and three studies looked at either the DASH diet or a variation of the DASH diet,74 76 or a vegetarian diet.80 

Two of the seven studies examined the association between adherence to a dietary pattern and incidence of type 2 diabetes.79 80 Although the results of both studies showed a favorable association between either a Mediterranean-style or a vegetarian dietary pattern and incidence of type 2 diabetes the studies differed in design and dietary pattern used to assess diet exposure. The other studies examined the intermediate outcomes of impaired glucose tolerance and/or insulin resistance and are discussed in the next section.

Dietary Patterns and Intermediate Outcomes

Five studies examined adherence to a dietary pattern and intermediate outcomes related to glucose tolerance and/or insulin resistance: two RCTs23 46 and three prospective cohort studies.29 31 64 It was difficult to assess food components across these studies, as numerous different scores were used and no compelling number of studies used any one score or index. Even so, favorable associations between dietary patterns and intermediate outcomes were found.

The two RCTs were conducted in populations in Europe that were at risk of diabetes. An early report from the PREDIMED trial showed that a Mediterranean diet decreased fasting blood glucose, fasting insulin, and HOMA-IR scores in a Spanish population at risk of CVD.23 In the Oslo Diet and Exercise Study (ODES), increased adherence to the authors’ a priori diet score resulted in decreased fasting insulin and insulin after a glucose challenge, but not fasting glucose, in Norwegian men with metabolic syndrome.46 Results from prospective cohort studies were consistent in showing a favorable association between diet score and fasting glucose, fasting insulin or HOMA-IR,29 31 with the exception of one study that found the association with fasting glucose only in men.64 

Data-Driven Approaches

Variations in populations studies, definition of outcomes, dietary assessment methodologies, and methods used to derive patterns resulted in a highly variable set of dietary patterns, thus making it difficult to draw conclusions from studies using data-driven approaches. For example, one study measured fasting blood glucose with a cutoff of 6.1 and greater mmol/L;47 another study measured plasma glucose with a cutoff of 5.1 and greater mmol/L,81 while a third study measured plasma glucose after an overnight fast and after a standard 75 g oral glucose tolerance test.82 Three prospective cohort studies assessed the association between dietary patterns and plasma glucose levels. Two U.S. studies derived patterns using cluster analysis47 81 and one study conducted in Denmark used factor analysis.82 Duffey et al. identified two diet clusters: “Prudent Diet” and “Western Diet”;47 Kimokoti et al. identified five clusters: “Heart Healthier,” “Lighter Eating,” “Wine and Moderate Eating,” “Higher Fat,” and “Empty Calories”;81 and Lau et al. derived two factors: “Modern” and “Traditional.”82 

For additional details on this body of evidence, visit: References 2, 58, and Appendix E-2.28

Dietary Patterns and Cancer

Existing Evidence around Foods and Nutrients and Cancer

The role of dietary composition in cancer risk has been postulated since ancient times, yet scientific evidence for such relationships was sparse until nearly a century ago. Experimental models of cancer based upon chemical carcinogens, radiation, viral-transmission, and inherited genetic variations gradually emerged in first half of the 20th century and were soon found to be influenced by dietary and nutritional interventions. The establishment of population-based cancer registries around the globe in the years following World War II clearly indicated that the incidence and mortality of specific cancers and the patterns of cancers varied widely between countries. Soon, studies of migrant populations demonstrated that in parallel with acculturation, cancer risk evolved toward that observed in the adopted country, implicating a strong role for environmental influences, such as dietary patterns, in cancer risk. When coupled with national food consumption data, relationships between dietary patterns or components and cancer risk were hypothesized. The development of dietary assessment tools, such as FFQs, paved the way for large prospective epidemiologic cohort studies designed to examine more precisely the role of dietary patterns, foods, and specific nutrients in the risk of various cancers.83 Additional diet assessment tools, such as food diaries, and single and multi-day 24-hr recalls enhanced the ability to undertake population studies and mechanism-based RCTs. These studies were made possible by USDA support of research to advance laboratory methods to define the nutrient content of foods in the U.S. food supply and establish a database that, when coupled with diet assessment tools, provides an estimated intake of energy, macronutrients, vitamins, minerals and other dietary variables. More recently, inclusion into the database of non-nutrient bioactive components primarily found in vegetables and fruits has enhanced the ability to define human intake of bioactive components that may affect health and disease.

In 1982, the American Institute for Cancer Research (AICR), a part of the World Cancer Research Fund (WCRF) global philanthropic network, was established. Together, the mission of WCRF/AICR is to fund research and disseminate evidence-based cancer prevention guidelines to the public. In 1997, the AICR/WCRF published the results of a comprehensive multi-year effort to systematically review the published scientific literature and develop dietary guidelines for cancer prevention.84 With a rapid expansion of available data in the subsequent years, the process was repeated for the 2007 AICR/WCRF report.85 This effort has been enhanced in subsequent years by the AICR/WCRF Continuous Update Project (CUP), in which data are reviewed and updated on a continuous, rolling basis for specific cancers, with several reports completed annually.86 This effort is accomplished through a rigorous systematic review process in which scientific evidence is gathered, reviewed and judged by panels of experts in nutrition and cancer in order to generate nutrition and cancer prevention goals for policy makers, the general population, and individuals seeking to reduce cancer risk.87 The most recent summary of the systematic review which documents important information about the relationship between specific foods, nutrients and other lifestyle behavior and cancer risk is found in Table D2.2.

As previously mentioned, the 2015 DGAC chose to determine whether an examination of dietary patterns, could inform the understanding of diet and cancer risk. As this scientific literature is relatively early in its development, we limited our search to the four most common malignancies affecting the American public—lung, breast, colon/rectal, and prostate—which account for the majority of the cancer burden in the United States. Although the published literature on dietary patterns and cancer risk is relatively young, the DGAC felt it was important to examine the evidence and conclusions, consider the implications for development of dietary guidelines, and indicate areas for future research.

Table D2.2. American Institute for Cancer Research / World Cancer Research Fund (AICR/WCRF) Summary of Strong Evidence on Diet, Nutrition, Physical Activity, and Cancer Prevention, updated 2014

↓↓ Convincing decreased risk.

 ↓   Probable decreased risk.

↑↑ Convincing increased risk.

 ↑   Probable increased risk.

 •   Substantial effect on risk unlikely.

Mouth, Pharynx, Larynx (2007)

Nasopharynx (2007)

Esophagus (2007)

Lung (2007)

Stomach (2007)

Pancreas (2007)

Gall bladder (2007)

Liver (2007)

Colorectum (2011)

Breast Premenopause (2010)

Breast (Postmenopause (2010)

Ovary (2014)

Endometrium (2013)

Prostate (2014)

Kidney (2007)

Skin (2007)

Foods containing dietary fiber

↓↓

Aflatoxins

 ↓  ↓  ↓ ↑↑

Non-starchy vegetablesi

 ↓

Allium vegetables

 ↓

Garlic

 ↓  ↓  ↓  ↓

Fruitsii

↑↑

Red meat

↑↑

Processed meat

Cantonese-style salted fish

 ↑

Diets high in calciumiii

 ↓

Salt, salted and salty foods

 ↑

Glycemic load

 ↑

Arsenic in drinking water

↑↑  ↑

Mate

 ↑

Alcoholic drinksiv

↑↑ ↑↑  ↑  ↑ | ↑↑ ↑↑ ↑↑  •

Coffee

 •  ↓  •

Beta-carotenev

↑↑  •  •

Physical activityvi

↓↓  ↓  ↓

Body fatnessvii

↑↑ ↑↑  ↑ ↑↑  ↓ ↑↑  ↑ ↑↑  ↑ ↑↑

Adult attained height

↑↑ ↑↑  ↑ ↑↑ ↑↑  ↑

Greater birth weight

 ↑

Lactation

↓↓ ↓↓

i Includes evidence on foods containing carotenoids for mouth, pharynx, larynx; foods containing beta-carotene for esophagus; foods containing vitamin C for esophagus.

ii Includes evidence on foods containing carotenoids for mouth, pharynx, larynx, and lung; foods containing beta-carotene for esophagus; food containing vitamin C for esophagus.

iii Evidence is from milk and studies using supplements for colorectum.

iv Convincing increased risk for men and probably increased risk for women for colorectum. Evidence applies to adverse effect for kidney.

v Evidence derived from studies using supplements for lung.

vi Convincing increased risk for colon not rectum.

vii Probable increased risk for advanced not non-advanced prostate cancer.

AICR/WCRF Evidence Stratification87

Convincing:
The evidence for a convincing grade is strong enough to support a causal relationship. This relationship is robust enough that it is unlikely to be modified of research in the foreseeable future. A grade of “convincing” requires evidence from more than one study type, data from at least two cohort studies, no unexplained heterogeneity between study types with regard to the presence or absence of an association, good quality studies where random or systematic errors are unlikely, presence of a dose-response relationship, and strong and plausible experimental evidence relating typical human exposures to relevant cancer outcomes.

Probable:
The criteria for determining a probable diet and cancer relationship include: evidence from at least two cohort studies or at least five case-control studies, no substantial unexplained heterogeneity between or within study types in the presence or absence of an association or direction of effect, good quality studies where the likelihood of random or systematic error is low, and evidence for biologic plausibility.

Limited—suggestive:
This grade is assigned when the evidence is too limited to permit a probable or convincing judgment, but there is evidence of a direction of effect. The evidence may have methodological flaws, or there may be a limited number of studies. A grade of “limited-suggestive” requires the following: evidence from at least two cohort studies or five case-control studies, there is some evidence for biologic plausibility, and the direction of the effect is generally consistent, although there may be some unexplained heterogeneity.

Limited—no conclusion:
This grade describes diet and cancer relationships where the evidence was ample for review by the panel, but it was too limited to receive one of the other grades. The available studies may be of good quality, but limited in number or yielding inconsistent results.

Substantial effect on risk unlikely:
This grade is assigned when the evidence is strong that a particular nutrient, food, dietary pattern, or physical activity is unlikely to have a substantial causal relationship to a cancer outcome. Data must be strong enough that modification in the foreseeable future is unlikely.

Question 4: What is the relationship between dietary patterns and risk of cancer?

Source of evidence: NEL systematic review

Conclusions

Colon/Rectal Cancer: Moderate evidence indicates an inverse association between dietary patterns that are higher in vegetables, fruits, legumes, whole grains, lean meats/seafood, and low-fat dairy and moderate in alcohol; and low in red and/or processed meats, saturated fat, and sodas/sweets relative to other dietary patterns and the risk of colon/rectal cancer. Conversely, diets that are higher in red/processed meats, French fries/potatoes, and sources of sugars (i.e., sodas, sweets, and dessert foods) are associated with a greater colon/rectal cancer risk. DGAC Grade: Moderate

Breast Cancer: Moderate evidence indicates that dietary patterns rich in vegetables, fruit, and whole grains, and lower in animal products and refined carbohydrate, are associated with reduced risk of post-menopausal breast cancer. The data regarding this dietary pattern and pre-menopausal breast cancer risk point in the same direction, but the evidence is limited due to fewer studies. DGAC Grade: Moderate for postmenopausal breast cancer risk; Limited for premenopausal breast cancer risk

Lung Cancer: Limited evidence from a small number of studies suggests a lower risk of lung cancer associated with dietary patterns containing more frequent servings of vegetables, fruits, seafood, grains/cereals, and legumes, and lean versus higher fat meats and lower fat or non-fat dairy products. Despite reported modest significant reductions in risk, definitive conclusions cannot be established at this time due to the small number of articles, as well as wide variation in study design, dietary assessment, and case ascertainment. DGAC Grade: Limited

Prostate Cancer: No conclusion can be drawn regarding the relationship between dietary patterns and the risk of prostate cancer. This is due to limited evidence from a small number of studies with wide variation in study design, dietary assessment methodology and prostate cancer outcome ascertainment. DGAC Grade: Grade not assignable

Implications

The data accumulating regarding the impact of dietary patterns on risk of certain types of cancers supports the concept that a healthy dietary pattern may significantly reduce the overall burden of cancer in the United States. Emerging studies on dietary patterns support the findings of expert reviews regarding individual foods and nutrients. Effective strategies to initiate early in life and maintain a healthy dietary pattern and body weight, coupled with regular physical activity, will significantly reduce the cancer burden in America.

Review of the Evidence

Dietary Patterns and Colorectal Cancer

This systematic review included 21 articles from prospective cohort studies and one article from an RCT published since 2000 that examined the relationship between dietary patterns and risk of colorectal cancer.88-109 The articles used diverse methodology to assess dietary patterns. Nine articles used indices/scores to assess dietary patterns, 10 articles used data-driven methods, and three used other approaches.

The dietary patterns examined in this systematic review were defined in various ways, making comparisons between articles difficult. However, despite general heterogeneity in this body of evidence, some protective dietary patterns emerged, particularly in articles where patterns were defined by index or score; articles using data-driven methods were less consistent. Patterns emphasizing vegetables, fruits, fish/seafood, legumes, low-fat dairy, and whole grains were generally associated with reduced risk of colorectal cancer. Patterns higher in red/processed meats, potatoes/French fries, and sodas/sweets/added sugars were generally associated with increased risk of colorectal cancer.

The relationship between dietary patterns and colorectal cancer risk often varied by sex and tumor location. Results based on analysis by sex were mixed, while analysis in tumor subgroups seemed to indicate that dietary patterns may be more strongly associated with tumor development in distal regions of the colon/rectum. Although most cohort studies make extensive efforts to include participants across a wide range of race/ethnic groups and across the socio-economic continuum, there still may be some groups for which the association between dietary patterns and colorectal cancer risk cannot be reliably assessed and therefore conclusions cannot be drawn.

Dietary Patterns and Breast Cancer

This systematic review included 25 prospective cohort studies and one RCT published since 2000 that examined the relationship between dietary patterns and risk of breast cancer.94, 101, 104, 110-131 The studies used multiple approaches to assess dietary patterns and cancer risk. Eight studies used indices/scores to assess dietary patterns, 13 studies used factor or principal components analysis, two used reduced rank regression, two made comparisons on the basis of animal product consumption, and one conducted an RCT of a low-fat dietary pattern.

This moderate body of evidence encompassed a large diversity in methods to assess or determine dietary patterns, making comparison across studies challenging. Despite this variability, 17 of the included studies found statistically significant relationships between dietary patterns and breast cancer risk, particularly among certain groups of women. Because a variety of different methodologies were employed to derive dietary patterns, and the patterns, while similar in many respects, were composed of different combinations of foods and beverages, it was difficult to determine which patterns had the greatest impact on breast cancer risk reduction.

The relationship between dietary patterns and breast cancer risk may be more consistent among postmenopausal women, but additional research is needed to explore the relationships for both pre- and post- menopausal cancer. Certain histopathologic and molecular phenotypes of breast cancer may be affected more by certain dietary patterns, but this has not yet been explored sufficiently. For example, limited studies to date suggest that estrogen or progesterone receptor status of breast cancers may define subgroups with unique dietary risk profiles, but no conclusions can be drawn at this time. More research is needed to explore other factors that may influence the relationship between dietary patterns during various stages of life and breast cancer risk, such as anthropometrics, BMI (including weight change over adulthood), physical activity, sedentary behavior, and reproductive history, including ages of menarche, age of menopause, parity, and breast feeding.

Dietary Patterns and Lung Cancer

This systematic review included three prospective cohort studies and one nested case-cohort study published since 2000 that examined the relationship between dietary patterns and risk of lung cancer.101, 104, 132, 133 The studies used different methods to assess dietary patterns. Two studies used an index/score to measure adherence to a dietary pattern, one study derived dietary patterns using principal components analysis, and another based dietary patterns on participant reports of animal product intake. With only four relevant studies that used different approaches for assessing or determining dietary patterns, the evidence available to examine the relationship between dietary patterns and risk of lung cancer is limited.

Dietary Patterns and Prostate Cancer

This systematic review included seven prospective cohort studies (from six different cohorts) published since 2000 that examined the relationship between dietary patterns and risk of prostate cancer.101, 134-139 The studies used different methods to assess dietary patterns. Three studies used index/scores to assess dietary patterns, two studies used factor analysis, one study used principle components analysis, and one made comparisons on the basis of animal product consumption.

Most of the seven studies included in this systematic review did not detect clear or consistent relationships between dietary patterns and risk of prostate cancer, though one found that adherence to the Dietary Guidelines (assessed using the HEI-2005 and AHEI-2010) was associated with a lower risk of prostate cancer, particularly among men who had a prostate-specific antigen screening in the past 3 years. Because these studies used a range of different approaches for assessing dietary patterns in populations with variable cancer screening patterns, had heterogeneous prostate cancer outcome ascertainment, and were typically limited to dietary exposure late in life, the results were inconclusive regarding risk for clinically significant prostate cancer.

For additional details on this body of evidence, visit: http://NEL.gov/topic.cfm?cat=3344

Dietary Patterns and Congenital Anomalies

Existing Evidence around Foods and Nutrients and Congenital Anomalies

It is well established that adequate folate status is critical for the prevention of neural tube defects, specifically anencephaly and spina bifida, as well as other birth defects.140 Folate is often described by its source, with “folate” referring to naturally occurring folate from food sources, and “folic acid” referring to the synthetic form used in dietary supplements and food fortification. After mandatory fortification of enriched cereal products with folic acid in 1998, serum folate concentrations in the U.S. population more than doubled, and rates of neural tube defects decreased by 20 to 30 percent.141, 142 

Despite this decrease, nearly one fifth of females ages 14 to 30 years do not meet the estimated average requirement for folate, the level deemed to be adequate for one half of healthy females in the age group.143 The current U.S. Preventive Services Task Force recommends that women capable of becoming pregnant should take 400 to 800 micrograms of folic acid daily from fortified food or supplements in addition to a healthy diet rich in food sources of folate and folic acid to reduce risk of neural tube and other birth defects.144 Women with a history of a pregnancy affected by a neural tube defect or who are at high risk of neural tube defects require 4 mg of synthetic folic acid supplements daily under the supervision of a physician.145 Given the emphasis on a healthy diet, the DGAC was interested in understanding which dietary patterns, if any, were associated with a decreased risk of congenital anomalies among women of reproductive age.

Question 5: What is the relationship between dietary patterns and risk of congenital anomalies?

Source of evidence: NEL systematic review

Conclusion

Limited evidence suggests that healthy maternal dietary patterns during the preconception period that are higher in vegetables, fruits, and grains, and lower in red and processed meats, and low in sweets were associated with lower risk of developing of neural tube defects, particularly among women who do not take folic acid supplements. Whereas some dietary patterns were associated with lower risk of developing anencephaly, others were associated with lower risk of developing spina bifida.

Evidence is insufficient to determine an association between maternal dietary patterns and congenital heart defects or cleft lip/palate.

All studies were consistent in demonstrating that folic acid supplementation periconceptionally was associated with a decreased risk of having a child with a birth defect (e.g. neural tube defects, congenital heart defects, and cleft lip/palate). DGAC Grade: Neural Tube Defects – Limited; Congenital Heart Defects – Grade not assignable; Cleft Lip/Palate – Grade not assignable

Implications

Women of reproductive age should consume folic acid in the form of a supplement or through fortified foods in the range recommended by the U.S. Preventive Services Task Force (400 to 800 micrograms) in addition to consuming a diet rich in vegetables, fruits, and grains; lower in red and processed meats; and low in sweets.

Review of the Evidence

This series of systematic reviews included five case-control studies (using data from three cohorts) published since 1980 that examined the relationship between maternal dietary patterns and congenital anomalies in infants.146-150 Three articles examined neural tube defects,146 two articles examined congenital heart defects,147 and two articles examined orofacial clefts.146

Although all five case-control studies reported significant associations between dietary patterns and risk of congenital anomalies in women not taking folic acid supplementation, the variability of dietary patterns methodology used and composition of dietary patterns identified made it difficult to draw conclusions. All studies were consistent in finding that folate delivered periconceptionally in food or as a supplement as a key nutrient was associated with lower risk of developing congenital anomalies. It should be noted that some of the included studies were conducted in countries with mandatory folate fortification, while others were from countries that prohibit such fortification.

For additional details on this body of evidence, visit: http://NEL.gov/topic.cfm?cat=3356 

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