I was a member of the 2010 Dietary Guidelines Advisory Committee (DGAC) and am honored to have served in this role. Making laws and making sausage are often compared; both are messy and not fun to watch. In the past, I have always been on the outside looking in on the Dietary Guidelines process, wondering why bigger changes were never made and why it took 5 years to publish a little pamphlet with broad dietary guidelines. I now appreciate the amount of effort it takes to develop and support dietary guidelines and also appreciate the implications that dietary guidelines have on federal nutrition and feeding programs, food product developers, and consumers.
HISTORY OF THE DIETARY GUIDELINES
In 1980, Nutrition and Your Health: Dietary Guidelines for Americans, was issued in response to the public’s desire for authoritative, consistent guidelines on diet and health. Public Law 101–445, Section 3, requires publication of the Dietary Guidelines at least every 5 years. They represent federal nutrition policy established jointly by the US Department of Agriculture (USDA) and the Department of Health and Human Services (HHS). They are designed to provide science-based advice for those 2 years or older to help prevent chronic diseases and promote health. They lay the foundation for federal nutrition programs and nutrition education programs and serve as a basis for research gaps and priorities. They are designed to ensure that messages and materials are consistent throughout the federal government and that government speaks with “one nutrition voice.”
The Dietary Guidelines have evolved over time to be more detailed and more prescriptive (Figure 1). The report of the DGAC on the Dietary Guidelines for Americans (DGA) 2010 is 445 pages long, whereas the DGA 2010 is a 95-page document. In contrast, the 1980 DGA was a short consumer brochure with 7 general recommendations:
1. Eat a variety of foods.
2. Maintain ideal weight.
3. Avoid too much fat, saturated fat, and cholesterol.
4. Eat foods with adequate starch and fiber.
5. Avoid too much sugar.
6. Avoid too much sodium.
7. If you drink alcohol, do so in moderation.
Although these Dietary Guidelines are quite broad, they are based on the quite specific Dietary Goals for American that were published in 1977.
The Senate Select Committee on Nutrition and Human Needs proposed Dietary Goals for the United States (the McGovern Report). These goals were as follows:
1. Increase carbohydrate intake to account for 55% to 60% of energy intake.
2. Reduce fat consumption to 30% of energy.
3. Modify the composition of dietary fat to provide equal proportions of saturated, monounsaturated, and polyunsaturated fatty acids.
4. Reduce cholesterol consumption to 300 mg/d.
5. Reduce sugar consumption by 40%.
6. Reduce salt consumption to 3 g/d.
The committee suggested that these goals could be met by increasing the consumption of fruits, vegetables, whole grains, poultry, fish, skim milk, and vegetables oils and by decreasing the consumption of whole milk, meat, eggs, butterfat, and foods high in sugar, salt, and fat.
There has been little change in the content of the Dietary Guidelines over time. The third edition, released in 1990, included numerical rather than directional recommendations, such as consume no more than 30% of calories from total fat. The 2000 edition of the guidelines added a food safety guideline (keep food safe to eat) and more specific food recommendations such as “let the pyramid guide your food choices.”
The 2005 committee included guidelines for whole grains (make half your grains whole) and recommendations to reduce trans-fat intake to as low as possible. The 2005 DGA noted that two-thirds of the American public were overweight. The 2005 DGA identified 41 key recommendations, 23 for the general public and 18 for special populations, children, women of child-bearing age, and the elderly. The 2010 DGA was equally detailed, but included a call to action for organizations, communities, businesses, and policymakers to support changes in behavior, the environment, and the food supply.
The need for “numbers” in the DGAs is driven by the relationship between the DGAs and federal nutrition programs.1 Nutrition assistance programs such as school lunch and the Special Supplemental Nutrition Program for Women, Infants, and Children are required to base regulations on the “most recent scientific knowledge,” which in the United States would be the DGAs.
Influences on the Process
The most common question I get when speaking about serving on the Dietary Guidelines Advisory Committee is how much influence do industry and commodity groups have on the process. The perception is that the process is controlled by commercial interests, and scientists on the committee are influenced by food companies and commodity groups. This is absolutely not the case. The process of developing the dietary guidelines is an open process with input available to any person or organization who wants to contribute. In fact, nominating qualified scientists to serve on the 2015 DGA can be done by anyone.
CALLOUT: ANYBODY AND EVERYBODY CAN EXPRESS THEIR VIEWS TO THE DIETARY GUIDELINES ADVISORY COMMITTEE
The 13-member 2010 DGAC was composed of scientists with a broad range of expertise representing nutrition, physical activity, food behavior, and nutritional changes through the life cycle. The Advisory Committee met 6 times publicly to agree on questions to examine in order to set nutrition policy. These meetings were open to the public; public comments are solicited throughout the process. The DGAC report is prepared and presented to the secretaries of USDA and HHS, which occurred in June 2010. At this point in the process, the Advisory Committee is dismissed and has no other input into the Dietary Guidelines. USDA and HHS write the policy document, and the Dietary Guidelines were released, which took place on January 31, 2011.
ADDRESSING QUESTIONS AND EVALUATING EVIDENCE
The DGAC works in subcommittees to address questions of diet and disease risk. Subcommittees in 2010 included energy balance, carbohydrates and protein, fats, nutrient adequacy, sodium and fluids, alcohol, and food safety. I served as the chair of the carbohydrate and protein committee and also served as a member of the energy balance committee and the nutrient adequacy committee.
How exactly do the DGAC and the subcommittees go about addressing the agreed-upon questions on the relationships of diet to health outcomes? The 2010 Advisory Committee used evidence-based review process with a hierarchy of evidence (Figure 2). Strongest evidence is found in randomized controlled trials, preferably double-blind. Of course, food studies suffer in this arena because it is difficult or impossible to blind food treatments; subjects know they are consuming an apple or apple juice. These types of trials can work with nutrients, as nutrients can be added to food or drinks without the knowledge of the participants or investigators (double-blind). The next strongest studies are prospective cohort studies, studies where a group or cohort of subjects are studied over time. Food frequency instruments are often used to collect dietary information before any diagnosis of disease, making these studies more reliable than cross-sectional studies. No case-control studies, animal research, or in vitro studies are included in DGAC review, and typically cross-sectional studies are included only if no stronger prospective studies are available for review.
The body of evidence for each question is then examined, and in an evidence-based review, conclusions can be deemed strong, moderate, limited, or lacking data to support them. There may be strong evidence that there is no relationship. For example, there was strong evidence of no relationship between glycemic index and disease outcomes.
Agreeing on the strength of the relationship is difficult because, for each question, different types of studies have been published. For each question, the 2010 Dietary Guidelines Advisory Committee addressed in the evidence-based report, the search criteria, inclusion and exclusion criteria for studies, the range of dates searched, and other information used in the review are all available on the USDA portal. The transparency used in an evidence-based approach is designed to minimize bias.
CHALLENGES IN EVALUATING DIET AND DISEASE RELATIONSHIPS
Inconsistencies in the DGAC report exist, often because of differences in inclusion criteria for studies. For example, limited evidence was found for a relationship between intake of sugar-sweetened beverages and body weight in adults in the carbohydrate chapter, when cross-sectional studies were excluded. In contrast, strong evidence was found between intake of sugar-sweetened beverages and body weight in children when cross-sectional studies were included in the review conducted by the energy balance committee.
Issues with contradictory evidence in the DGAC 2010 report were reviewed by Hite et al.2 They suggest that the report does not provide sufficient evidence to conclude that increases in whole grain and fiber and decreases in dietary saturated fat, salt, and animal protein will lead to positive health outcomes. They state that lack of supporting evidence limits the value of the proposed recommendations as guidance for consumers or as the basis for public health policy. They suggest that it is time to reexamine how US dietary guidelines are created and ask whether the current process is still appropriate for our needs. Their support of lower carbohydrate intakes, a view shared by many of the public comments to the DGAC, is definitely an area needing more discussion for the 2015 Dietary Guidelines.
CHALLENGES OF DIETARY GUIDANCE
Humans have survived on a wide range of diets, mostly reflecting access to food supply. Although protein needs are set based on ideal body weight (0.8 g/kg body weight for adults), the amounts of carbohydrates and fats in healthy diets vary great. Traditional Eskimo diets contain 80% of calories as fat, whereas traditional African diets are 80% of calories as carbohydrates. Thus, the trick for good nutrition is to consume diets that contain the appropriate number of calories, adequate protein, and essential vitamins, minerals, and fluids.
Tools to help consumers choose adequate diets have evolved over the years (Figure 3). Because of the importance of adequate nutrition in growth, the first tools were designed for children. Later tools were called the Basic 7 and Basic 4. These teaching tools helped consumers build balanced diets by adhering to the core values of good nutrition: moderation and variety. The 2005 Mypyramid.gov was an attempt to provide more specificity to the system, but required that users input data into a Web site. The addition of the active figure on the model was considered innovative, but the circus tent design does not easily translate into food choices.
After the 2010 DGA was issued, myplate.gov was released as a tool to help plan diets (Figure 4). This tool was developed by government agencies without input from the 2010 DGAC. The tool is somewhat confusing because it is mostly food based, except for the protein portion of the plate, which is nutrient based. The plate is half fruits and vegetables, which is a good model for overweight, middle-aged adults, but might not work well for growing children, depending on food choices. The dairy depiction as a glass of milk might be confusing for consumers who do not appreciate they would also get credit for a serving of yogurt or cheese. One-quarter of the plate is grains. Closer reading of the myplate.gov materials suggests that myplate.gov is not supposed to be quantitative.
ACCEPTED NUTRITION FACTS
Traditionally, nutrient recommendations were made to prevent deficiency diseases. In 1941, the National Academy of Sciences began issuing recommended dietary allowances, the quantity of nutrients a person needs to consume daily to ensure basic good health, proper growth, and reproductive success and to prevent nutrient deficiency diseases. The current nutrition standards for the United States and Canada are the 2002 Dietary Reference Intakes. These standards include the recommended dietary allowance, but also adequate intakes for nutrients such as dietary fiber and choline and tolerable upper level intake, estimates of intakes of nutrients that could cause potential harm. Dietary deficiency diseases have been virtually eliminated in the United States, thanks to the enrichment of refined grains with thiamin, riboflavin, and niacin and the consumption of fortified foods such as ready-to-eat breakfast cereals.
A second universally accepted dietary principle is to maintain appropriate body weight by consuming only enough food to balance the amount of energy expended. This has become much more difficult as modern life has removed all needs for physical labor, and tasty foods are inexpensive and easily obtainable.
Dietary recommendations to prevent chronic diseases have always been controversial. Alfred E. Harper,3 in his article, “Killer French Fries: The Misguided Drive to Improve the American Diet,” describes our ways of learning about nutrient deficiencies and how such a model does not work for chronic diseases such as heart disease and cancer. He also points out misinformation in the early Dietary Guidelines reports. For example, fruits are listed as a source of “complex carbohydrates,” when in reality they are mostly a source of sugar and often are poor sources of nutrients including vitamins and minerals. The high-protein quality and quantity of animal products have been lost in our translation of dietary guidance for public health. As Harper suggests, clinical advice to change diet based on the need to lower serum cholesterol is much different than public health advice to suggest that all Americans should consume plant foods of low protein quality.
The Dietary Goals were always controversial and were not universally supported. In the second edition of the Dietary Goals, 5 members supported the goals (Dr D. M. Hegsted, Harvard School of Public Health; Dr Beverly Winikoff, Rockefeller Foundation; Dr Philip Lee, University of California, San Francisco; Sen Robert Dole; and Sen George McGovern). In contrast, Senator Charles Percy of Illinois wrote a negative comment in the forward to the Dietary Goals. He stated that “science cannot at this time ensure that an altered diet will provide protection from certain killer diseases such as heart disease and cancer.” Supplemental Views of the Dietary Goals, many negative, were published in an 869-page supplement. Thus, Dr Harper was not the only dissenting voice for adoption of universal Dietary Goals for the United States, although he published many review articles on his concerns with Dietary Goals.
AN EVIDENCE-BASED APPROACH
Although the recommendations of the Dietary Guidelines have not changed significantly since the 1980s, the development of the Dietary Guidelines policy has become more open and science-based. Questions on the relationship between dietary exposure and disease outcome are challenging and contentious. I will describe 2 topics, carbohydrate as an example of a macronutrient and fruits and vegetables as an example of a food group.
The amount of dietary carbohydrate that confers optimal health in humans is unknown. Adults should consume 45% to 65% of their total calories from carbohydrates, except for younger children, who need a somewhat higher proportion of fat in their diets. Vegetables, fruits, whole grains, milk, and milk products are the major food sources of carbohydrates. Grains and certain vegetables including corn and potatoes are rich in starch, whereas sweet potatoes are mostly sucrose, not starch. Fruits and dark green vegetables contain little or no starch. Regular soft drinks, sugar/sweets, sweetened grains, and regular fruitades/drinks comprise 72% of the intake of added sugar.4
Marriott et al4 examined the intake of added sugars and selected nutrients from 2003 to 2006 National Health and Nutrition Examination Survey data. Thirteen percent of the population had added sugars intake of more than 25% of calories. The predominant issue of concern was the overall high calorie and low quality of the US diet, not added sugars.
Limited data exist that added sugar intake is linked to any adverse health outcome. Generally, intake of all types of carbohydrates is linked to lower body weight in prospective cohort studies.5 It is difficult to measure added sugar in epidemiologic studies, so intake of sugar-sweetened beverages is the proxy for added sugar intake. In prospective cohort studies, there are few data that intake of sugar-sweetened beverages is linked to higher energy intake or body weight in adults.
Food modeling is a process where USDA food patterns are used to describe the types and amounts of foods that can be consumed to achieve nutritional adequacy. In these examples, foods and beverages with added sugar removed are more nutrient dense. Figure 5-2 in the DGA 2010 gives examples where added sugars are removed to make the food more “nutrient dense.” Although these examples work well in computer-based food modeling, it is likely that these maneuvers may not improve food choices.
The cereal industry has worked hard to remove added sugar from breakfast cereals, but in many cases, added sugars have been replaced by refined starches. Thus, the grams of added sugar are reduced in the product, but the starch content increases, so there are no differences in the calorie content of the cereal. This, obviously, will have no positive impact on body weight or public health.
Chocolate milk is another example of the difficulties with a policy based on reducing content of added sugar in the food supply. Many school districts are banning chocolate milk because of its relatively high content of added sugar. Although the thinking in a boardroom is that children will select the default beverage “low-fat milk” instead of chocolate milk, most studies find that if flavored milk is not available, children choose not to drink milk at all. Thus, the unintended consequence of a well-intentioned policy (reduce added sugar intake by banning chocolate milk) is that children consume less milk. The nutrients provided by the dairy group, protein, vitamin D, and calcium, for example, are not easily obtained in other typical eating patterns in the United States.
Fruits and Vegetables
Historically, consumption of certain plant foods, fruits, vegetables, and legumes was thought to prevent or cure ailments ranging from headaches to heart disease.6 Early medicine revolved around the prescription of specific foods for certain disorders. Many of these plant foods are also high in dietary fiber and phytoestrogens, so often the hypotheses were driven by fiber, carotenoids, phytoestrogens, or other plant chemicals. Of course, determining the relationship between any dietary component and health outcomes is difficult because diet is a complicated exposure; each day, we eat a variety of foods and nutrients, and the ability to link any particular food or nutrient to a health or disease outcome is limited.
In epidemiologic studies, it is possible to count the number of servings of fruits and vegetables consumed daily. Of course, fruits and vegetables consumed vary greatly in nutrient composition and calories per serving. The earliest definition of a fruit was “any plant used as food,” and a vegetable was a “plant, as opposed to an animal or inanimate object.”7 In the 18th century, botanical definitions were standardized, and the definition of a fruit was based on its anatomy, whereas that of a vegetable was based on culinary usage. Generally, culinary custom dictates which plant foods are considered vegetables or fruits. A drawback of using culinary definition is the misclassification of botanical fruits such as squash, tomatoes, and mature beans, which, from a culinary perspective, are considered vegetables.
Within each category, other classifications can be used. For example, for vegetables, raw, cooked, canned, pickled, leafy green, and legumes are often examined. Fruits and vegetables have also been described as part of a phytochemical group—for example, carotenoids, vitamin C, or folate.7 The 2005 DGA recommended “choose a variety of fruits and vegetables each day. In particular, select from all 5 vegetable subgroups (dark green, orange, legumes, starchy vegetables, and other vegetables) several times a week.”
Earlier reviews that included cross-sectional studies found stronger support for the consumption of fruits and vegetables and disease prevention. Steinmetz and Potter6 concluded that the scientific evidence regarding a role for vegetable and fruit consumption in cancer prevention is generally consistent and supportive of current dietary recommendations. Yet, Hung et al,8 using data from the Nurses’ Health and Health Professionals cohort studies, concluded that increased fruit and vegetable consumption was associated with a modest, although not statistically significant, reduction in the development of major chronic disease. Smith-Warner et al9 examined data from 8 prospective studies of breast cancer and intake of fruits and vegetables. No association was found for total fruits, total vegetables, or total fruits and vegetables. No additional benefit was found in comparisons of the highest and lowest deciles of intake. Additionally, no associations were observed for green leafy vegetables, 8 botanical groups, and 17 specific fruits and vegetables. They conclude that fruit and vegetable consumption during adulthood is not significantly associated with reduced breast cancer risk.
More recent reviews of fruits, vegetables, and other diseases are also less positive on a role between intake of fruits and vegetables and disease protection. Dauchet et al10 suggest that evidence that fruit and vegetable consumption reduces risk of cardiovascular disease remains scarce thus far. They agree that, under rigorous controlled experimental conditions, fruit and vegetable consumption is associated with decreased blood pressure. Few experimental data exist that fruit and/or vegetable consumption affects blood lipids or other cardiovascular risk factors.
In a population-based cohort study in the Netherlands, higher consumption of fruit and vegetables, whether consumed raw or processed, was protective against coronary heart disease incidence.11 The risk of coronary heart disease incidence was 34% lower for participants with a high intake of total fruit and vegetables (>475 g/d) compared with participants with a low total fruit and vegetable consumption (<241 g/d).
A systematic review and meta-analysis of fruit and vegetable intake and incidence of type 2 diabetes included 6 studies, 4 of which provided separate information on the consumption of green leafy vegetables.12 No significant benefits on incidence of type 2 diabetes were found with increased consumption of vegetables, fruit, or fruit and vegetables combined.
Fruits, vegetables, and legumes vary widely in nutrient content, so they should not be expected to have similar physiological effects.13 Although dietary guidance is supportive of a more vegetarian eating pattern, including increased servings of fruits and vegetables, the scientific support for these recommendations is more historical than evidence based. Additionally, dietary recommendations to increase consumption of fruits and vegetables increase food costs.14
THE DIETARY GUIDELINES AND OUR HEALTH
Does adherence to the Dietary Guidelines make us healthier? This question is generally answered by cynical comments that no one adheres to the Dietary Guidelines anyway so it does not matter. Intervention studies, where diets following the Dietary Guidelines are fed long-term to human volunteers, do not exist. Generally, adherence to the Dietary Guidelines is measured in epidemiologic studies by determining a healthy eating index, a measure of adherence to the diet recommendations of the Dietary Guidelines. McCullough et al15 found that the healthy eating index was only weakly associated with risk of major chronic disease. Zemora et al16 determined the relationship between weight gain among black and white young adults in the Coronary Artery Risk Development in Young Adults study (1985–2005). The authors created a 100-point Diet Quality Index. They concluded that their findings do not support the hypothesis that a diet consistent with the 2005 Dietary Guidelines benefits long-term weight maintenance in young adults in America. They suggest the need for attention to obesity prevention in future Dietary Guidelines.
The DGAC report is an evidence-based, systematic review written by the DGAC. The DGAs are written by the government based on the DGAC report. Food guides, such as myplate.gov, are also written by government staff. The DGAC does not play a singular role in determining the DGAs or myplate.gov. The translational process—taking the scientific report and turning it into the DGAs—has been criticized for not being transparent to the public or even to the members of the DGAC.1
Efforts to micromanage the diet by imposing strict dietary rules are difficult to support with evidence-based nutrition science. Concepts such as added sugar and solid fats, which work well in computer-based food modeling, are not helpful to consumers attempting to select and consume a “healthier diet.” Clear label information on total calories in a consumed portion would be of benefit to consumers attempting to control calorie intake. We eat foods, not nutrients, and cultural norms and traditions must be considered when determining dietary guidance. Nutrient needs across the life cycle vary greatly, so general advice, although well-meaning, may actually be harming health status and making the obesity epidemic worse.
© 2012 Lippincott Williams & Wilkins, Inc.