A scientific report outlining new recommended dietary
guidelines is already drawing attention in Washington D.C.—less for its fresh
take on optimal diets than for its policy suggestions—and some of the authors
joined a symposium hosted at the Harvard T. H. Chan School of Public Health
(HSPH) yesterday to discuss their work. Against a stark background of data showing
that more than two-thirds of Americans (155 million people) are obese or
overweight, members of the 2015 Dietary Guidelines
Advisory Committee (DGAC), selected for their expertise in nutrition and
disease, have recommend less meat, sugar, and refined carbohydrates. Gone are
the limits on fat as a proportion of caloric intake: instead, the experts
recommend capping consumption of saturated
fats at 10 percent of total calories, and no longer suggest a limit on healthy,
unsaturated fats, such as those found in vegetable oils and nuts. Eggs and
shrimp, nutrient-rich foods once vilified for their cholesterol content, are
back on the menu now that scientific evidence shows only a weak link between
dietary cholesterol and cholesterol levels in the blood.
The recommendations of the independent, volunteer DGAC are
used by the U.S. Departments of Agriculture (USDA) and Health and Human
Services (HHS) to inform and update the federal Dietary Guidelines for Americans, the rules that shape
implementation of a host of federally funded programs and initiatives,
including meals served in schools. The new report’s inclusion of policy
suggestions—such as a tax on sugar (which now contributes 13 percent of
calories in the American diet) as one way to reduce public consumption of
sweetened beverages and foods—raised the ire of some members of Congress. Some
representatives have also criticized the report for addressing the
sustainability of the food supply. The guidelines have considered food security
since 1980, one member of the DGAC noted at the HSPH symposium, but have
previously focused on current circumstances. Now the group, which has added
seafood to the list of items considered beneficial for health, is considering
the long-term impact of human consumption patterns on critical ecosystems such
as global fisheries under the rubric “Food sustainability and Safety,” one of
five areas highlighted in the report.
In the keynote address at HSPH, J. Michael McGinnis—now executive
director of the Institute of Medicine Roundtable
on Value & Science-Driven Health Care (part
of the National Academy of Sciences) and previously a high-level administrator
at HHS, emphasized that the scope of the recommendations reflects the fact that
nutrition, which includes everything from food supply chains to food aid to
research, is “fundamentally a systemic activity.” Ideally, he emphasized, “the Dietary Guidelines for Americans should
offer the anchor reference point around which all food and nutrition policies
can orient.”
McGinnis also outlined what he hoped would become goals for
the next iteration of the report, due in 2020. These included more research on interaction
among different nutrients; what “actually works” for weight reduction; and the
ways in which individual biology and behavior influence health outcomes. He
concluded with “a modest proposal:” that public and private partners work
together to create “a sustained social-marketing message” that will promote
public adoption of the healthy eating patterns identified in the report.
DGAC chair Barbara Millen, formerly a professor at the
Boston University School of Medicine and now president of public health startup
Millennium Prevention, then explained the
scientific standards employed in the report. Randomized, controlled trials—the
gold standard in public-health research—were given the most weight, she said; association
studies that link behaviors or particular nutrients to health outcomes were accorded
less importance. “Strong” recommendations in the 2015 report thus rest on
firmer scientific foundations than ever before and represent, said Millen,
“immediately actionable recommendations” to HHS.
Members of the committee, some of them reporting remotely
via video feed, then presented key findings. They found that:
40 percent of the U.S. population doesn’t get
enough of vitamins A, D, E, and C, nor folate, calcium, magnesium, fiber, and
potassium—not surprising, perhaps, given that Americans don’t eat enough
vegetables, fruits, whole grains, and dairy.
Fully 70 percent of the population doesn’t eat
the recommended quantities of fruit. What do Americans eat? The largest caloric
contribution in most people’s diets comes from a category called “mixed
dishes,” the largest component of which includes burgers and sandwiches.
Many adolescent and pre-menopausal women are
deficient in iron.
The shortfalls in calcium, vitamin D, fiber, potassium, and
iron are considered “a public health concern” because underconsumption is
linked to adverse health outcomes.
Consumption of saturated fat and sodium, on the other hand,
exceed the maximal standard and thus pose health risks at the other extreme.
The average American consumes more than 3,400 milligrams (mg) per day, while
the upper recommended limit is 2,400 mg. The evidence that high sodium intake
leads to high blood pressure is strong, reported DGAC committee member Frank Hu,
professor of nutrition and epidemiology at HSPH and professor of medicine
at Harvard Medical School (HMS). There is also moderate evidence of a link
between sodium and cardiovascular disease, he reported.
The committee emphasized that a variety of different dietary
patterns ranging from a “healthy U.S. style,” to vegan and Mediterranean style lead
to healthy outcomes. Common to all of them, speakers emphasized, are
vegetables, fruits, whole grains, fish/seafood, legumes, and nuts. Healthy
diets include moderate amounts of low and non-fat dairy products and alcohol;
limit processed and red meat; and are low in sugar-sweetened beverages and
foods and refined grains.
Hu also conveyed the report’s finding of strong evidence
that moderate coffee consumption (three to five cups a day) does not lead to
increased long-term health risks in healthy individuals. In fact, coffee
drinkers appear to have lower risk of type 2 diabetes and cardiovascular
disease. The effects of caffeine itself are less well documented, he noted, but
up to 400 mg a day is safe and may protect against Parkinson’s disease. Higher
amounts may have adverse outcomes, especially when combined with alcoholic
beverages. (The report also noted that coffee drinkers should minimize the
amount of added cream, milk, and sugar.)
Earlier versions of the guidelines have already had a
positive impact on children’s dietary choices while in school, noted one author
somewhat ironically: “Kids are gaining weight in the summer,” indicating that
schools, by contrast, are doing “a good job.”
Americans’ level of physical activity, however, is far below
federal guidelines for both children and adults. Although 50 percent of adults
report meeting the minimum recommendations for activity, research making use of
accelerometers tells a different story. Those studies indicate that 90 percent
of the population does not meet even the minimum recommendations for physical
activity.
Stare professor of epidemiology and nutrition and HMS
professor of medicine Walter
Willett, an eminent expert on diet, ended the evening with a personal
assessment of the report’s findings. Noting how difficult the work of such
committees can be politically, he offered a constructive critique of the
report’s findings that Americans don’t consume enough calcium. He pointed out
that the scientific evidence for that assertion comes from studies of only two-
to three-weeks’ duration that have shown no link to decreased bone health. The
report guidelines, he continued, imply that Americans would need three servings
of dairy a day to get enough calcium—a recommendation that would dictate a
doubling of production, he argued, a massive expansion of the American dairy
herd, and thus one that “clashes” with the DGAC’s own consideration of
environmental impact.
He praised the committee for the enormous amount of work
they had put in during the last two years, and concluded by highlighting
several of the reports’s cutting-edge recommendations that will lead to better
public health, including the removal of the cap on calories from fat as a
percentage of a healthy diet, the suggested limits on consumption of red meat,
the emphasis on foods rather than nutrients, and the inclusion of
environmental issues that impact long-term sustainability of the food supply.