Lesson for the Next Dietary Guidelines Committee: We Need A Diversity of Opinion
An analysis of the last advisory committee to the Dietary Guidelines for Americans, our nation’s top nutrition policy, reveals little diversity of opinion on key dietary issues among the committee’s 14 members.
The Nutrition Coalition investigated the background of the 2015 Dietary Guidelines advisory committee (DGAC) and found that a large majority (11 out of 14, or nearly 80%) had consistently published work in favor of plant-based, low-animal-fat, vegetarian diets, and that many had built their careers promoting these types of diets.
Significantly, the 2015 Dietary Guidelines for the first time elevated the “Healthy Vegetarian” diet as one of three recommended dietary patterns even while the committee acknowledged that the evidence for this diet was “limited”— the lowest possible rank for available data.
Moreover, half of the 2015 committee members were epidemiologists (or working primarily in epidemiology), an inherently weak type of science that has been the source of major mistakes in the guidelines in the past. This is a type of science that is valuable for suggesting hypotheses but can almost never be used to establish cause-and-effect relationships—which is the kind of definitive proof that is needed as a basis for population-wide policies. An over-reliance this weak type of science, cannot be advisable.
The 2015 Committee: Little Diversity of Views
In 2015, the chair of the committee, epidemiologist Barbara Millen, published numerous papers on “Heart Healthy” diet patterns, which she characterized as being high in fruits and vegetables and low in “animal fats.” In 2011, she and her co-authors wrote, “there is an emerging consistency in the characteristics of diets that offer protective features (e.g., higher whole grains, complex carbohydrates, lower animal products, higher fruits and vegetables, vegetable proteins) or detrimental characteristics (e.g., high animal fat, salt and related condiments or pickled foods).” (Millen is the owner of a company in Westwood, MA that sells plant-based diet solutions, a leadership role she maintained while serving on the committee)
Millen repeated her idea about a healthy diet as a co-author of the American Heart Association (AHA) position paper on lifestyle in 2013. The paper also stated that a healthy diet “emphasizes vegetables, fruits and whole grains; includes low-fat dairy products, poultry, fish, legumes, nontropical vegetable oils and nuts; and limits intake of sweets, sugar-sweetened beverages and red meats.”
Tufts professor Alice Lichtenstein was another co-author of that AHA paper and, under Millen, Vice-Chair of the DGAC. As she wrote in a 2014 letter to the New York Times, a heart-healthy diet is one “that emphasizes vegetables, fruits and whole grains; includes low-fat dairy products, poultry, fish, legumes, nontropical vegetable oils and nuts; and limits intake of sweets, sugar-sweetened beverages and red meats.”
A third member of the 2015 DGAC, the epidemiologist Frank Hu from Harvard’s T.H. Chan School of Public Health, has an enormous volume of work spanning decades, with papers consistently demonstrating his preference for plant-based diets. Hu has written numerous papers finding that meat consumption is associated with obesity, type 2 diabetes, higher mortality and other diseases. He consistently links fruits, vegetables, nuts, plant proteins, and whole grains with positive health outcomes. He is also the most prolific author of papers asserting that saturated fats are bad for health and should be replaced by polyunsaturated fats. (Hu reports receiving funding from industries selling foods high in polyunsaturated fats, including vegetable oil giants Unilever and Bunge, the California Walnut Commission, and the Tree Nut Council.)
Cheryl Anderson, an epidemiologist from UC San Diego, has mainly examined the relationship between salt and kidney disease. When weighing in on diet for obese kidney patients in 2006, she wrote that a preferable diet was one low in fat and animal products while high in fruits and vegetables. Her papers on diet tend to cite the trials on DASH (Dietary Approaches to Stop Hypertension), which emphasize fruits, vegetables, grains, and low-fat dairy while discouraging meat and fat.
Steven Clinton of The Ohio State University appears to have spent most of his career trying to show that fruits and vegetables prevent cancer. He has specifically focused on the potential anti-cancer properties of lycopene, soy-isoflavones, black raspberry products, and the phytochemicals in tomatoes, including a novel tomato-soy nutraceutical. (Clinton was funded by the soybean industry for his soy-related trials.) “A diet rich in fruits and vegetables should be at the heart of cancer prevention efforts,” he is quoted as saying in the book A World Without Cancer.
Rafael Perez-Escamilla, an epidemiologist from the Yale School of Public Health, has, in his research, generally supported diets aligned with guidelines (i.e., diets low in saturated fats and high in fruits and vegetables). Addressing household food insecurity among Mexican adults in 2012, Perez-Escamilla and his co-authors wrote, “it is important that food assistance programs facilitate access to low energy density diets characterized by high fruit, vegetable and whole grains consumption and relatively low intake of foods rich in saturated fats.” As with others on the committee, however, these conclusions seem to be more aligned with existing recommended patterns rather than his own independent assessment of diets and health.
Anna Maria Siega-Riz, an epidemiologist from UNC-Chapel Hill, has done relatively little research on specific food patterns, with the exception of examining links between diet and the health of children, pregnant women, and the poor. Most of this research assesses dietary quality using the DASH score, which gives positive ratings to fruit, vegetable, grains and low-fat dairy while designating negative ratings to meat, processed meat, and saturated fats. Like Perez-Escamilla, Siega-Riz seems to focus on implementing existing recommendations rather than developing her own ideas about healthy diets.
Mary Story, a nutrition and food scientist from Duke University, promotes fruits and vegetables but, like Siega-Riz, appears to do so less out of her own independent determination and more from an acceptance of existing dietary guidelines. Story’s work has focused almost entirely on how food environments affect eating behavior. Her studies usually, if not always, define “healthier” eating as increased consumption of fruits and vegetables. A particular area of focus for Story has been increasing and assessing fruit and vegetable intake in adolescents, both at school and at home.
Miriam Nelson, founder of the Strong Women Initiative and Co-Founder of ChildObesity180 at Tufts University, has in the past sounded downright agnostic on the subject of vegetarianism. "The reality is, whether you eat high protein, low protein, high fat, or low carb, you can follow any of those diets and eat really, really well," she told Elle magazine in 2011. However, her 2010 book, The Strong Women's Guide to Total Health, specifically advises readers to eat more plant-based proteins and cites studies linking red meat consumption to heart disease and cancer. More recently, she has become a strong advocate of factoring sustainability into nutritional decision-making, which she believes involves dramatically cutting back on meat. Indeed in 2015, Nelson objected to the final Dietary Guidelines excluding sustainability as a rationale, calling it a “cave-in” to the private sector. “The evidence is strong that Americans need to eat less meat—especially red and processed meat,” she said. (Nelson has written 10 diet books, which together have sold over a million copies in 14 languages.)
Marian Neuhouser, an affiliate professor of epidemiology and head of the cancer prevention program at the Fred Hutchinson Cancer Research Center, has focused her work on adherence to traditional low-fat diets such as the Mediterranean and DASH diets. She has taken part in studies on Mexican and Chinese immigrants based on the premise that a diet low in fat and/or high-in-fruits-and-vegetables is healthy and has co-authored papers linking improved health outcomes to high consumption of fruit and vegetables. Other investigations on this diet by Neuhouser have yielded less conclusive results.
Lucile Adams-Campbell, an epidemiologist at Georgetown University, has researched energy balance, diet and exercise. In 2009, she co-authored a paper on dietary patterns and breast cancer risk among black women using two dietary patterns: “Western,” comprising refined grains, processed meat, and sweets, and a “prudent” diet high in whole grains, vegetables, fruit, and fish. The fact that meat, dairy and eggs are excluded from the “prudent” list reflects an assumption that these foods cannot promote good health.
Purdue University’s Wayne Campbell was the only committee member who had written favorably of both vegetarian and meat-based diets, concluding that each diet is healthy in different ways. Regarding protein, his work has generally shown either no negative effects or benefits from increased protein consumption, with few differences between meat and plant-based protein when corrected for dosage. (Campbell’s research has partly been funded by multiple meat and egg industries.)
Steven Abrams of Baylor has worked largely on nutrient absorption in adolescents. If anything, he has been attentive to the risks of plant-based diets such as low zinc absorption, yet he supported the DGAC recommendations when they came out. In an op-ed in the Huffington Post, he wrote, “For the first time, our committee suggested that we consider supporting diets lower in meat intake in favor of more seafood, fruits and vegetables… Of course, not everyone agrees with these recommendations. The meat industry does not like suggestions to increase fruit and vegetable consumption and decrease meat intake. But considerable evidence supports those changes, while allowing meat in the diet.” Abrams, alongside fellow DGAC members Nelson and Hu, supports plant-based diets at least partially due to sustainability considerations.
Finally, Tom Brenna, a nutritional biochemist from Cornell University, has published most of his papers on the potential benefits of omega-3 supplements and therefore has a limited written record on his preferred dietary patterns. When the guidelines came out, Brenna told NPR, “The message is, [for] those people who are overeating meat, eat less of it.”
Committee’s Bias Led to Predictable Results
Given that the vast majority of committee members supported plant-based diets, one might not be surprised that they introduced “Healthy Vegetarian” as one of three official USDA-HHS dietary patterns. (The others are “Mediterranean” and “US-Style”). Yet the committee could not identify any rigorous, i.e. “Grade 1” strong evidence, to support this recommendation.
Moreover, of the eight systematic reviews the DGAC conducted, examining whether fruits and vegetables could promote health benefits of any kind, only “inconclusive” evidence could be found. The elevation of a diet based on little-to-no rigorous evidence is a disturbing example of a non-evidence-based policy. It also reflects the possible influence of bias operating in the 2015 DGAC.
It’s important to remember that advice to eat plant-based diets has clearly not promoted health thus far , as Americans are now eating 44 percent more plant foods (excluding sugar) than they did in 1970, yet during this time rates of obesity or diabetes have only risen.
The last two decades have seen a diversification of expert views on dietary fats as well as on the role of plant vs. animal foods in the diet. It is therefore imperative that the next expert committee appointed by USDA-HHS include a greater balance of views on these topics as well as a greater diversity of expertise.