The latest available data show that, as of 2016, Americans had made some significant dietary improvements, reducing intake of low-quality carbohydrates like added sugars and increasing high-quality carbohydrates, plant protein, and polyunsaturated fatty acids. However, they were still eating too many low-quality carbohydrates and consuming more than the recommended level of saturated fat, according to researchers at Tufts’ Friedman School of Nutrition Science and Policy and the Harvard T.H. Chan School of Public Health.
The study, published recently in JAMA, analyzed data from nearly 44,000 U.S. adults aged 20 and older who took part in the National Health and Nutrition Examination Survey (NHANES) from 1996 to 2016. The researchers used the Healthy Eating Index 2015, which measures adherence to the 2015-2020 Dietary Guidelines for Americans (DGA), to examine overall diet quality; trends in intake of carbohydrates, protein, and fats; and major food sources of carbohydrate and protein. The study results can be considered a “report card” on America’s diet.
The Carb Conundrum: Contrary to popular belief, Americans do not consume too many carbohydrates, but it appears they eat the wrong ones. The data show that most carbohydrates Americans eat are low quality. Diets high in low-quality carbohydrates like sugar and refined grains are associated with higher disease risk, while diets that emphasize high-quality carbohydrates from foods like fruits, vegetables, and whole grains are associated with health benefits. “Fruits, vegetables, and whole grains are high in fiber and contain many other bioactive compounds,” says Fang Fang Zhang, MD, PhD, an associate professor at the Friedman School and senior and corresponding author on the study. “High dietary fiber intake has been associated with lower risk of obesity, type 2 diabetes, heart disease, stroke, and some cancers.”
During the study period, total carbohydrate intake decreased by two percent (from 52.5 to 50.5 percent), remaining in the recommended intake range of 45 to 60 percent of calories. Intake of low-quality carbohydrates decreased by three percent, but these less-healthful choices still made up nearly 42 percent of total calories. “Refined grains and added sugars are the two major components of low-quality carbs,” says Zhang. “We know from our previous studies that sugar-sweetened beverages contribute a large proportion of added sugar consumption in Americans’ diets. We did not study the major sources of refined grains but suspect that low-quality carbs may come primarily from processed packaged foods and fast foods.”
Intake of high-quality carbohydrates like whole grains and whole fruit only increased by around one percent (from 7.4 to 8.6 percent), and these choices made up only nine percent of total calorie intake. “It is surprising to see that nearly 42 percent of our daily calories come from low-quality carbs,” says Zhang. “In particular, our consumption of refined grains has been increasing in the past 15 years.”
The Protein-Fat Connection: Calories from protein and fat in the American diet each increased one percent. Half of the estimated intake of fat was saturated fatty acids, which have been associated with higher risk of cardiovascular disease. The other half came from heart-healthy mono- and polyunsaturated fatty acids.While the DGA recommend limiting saturated fat intake to no more than a 10 percent of calories, this study found that total saturated fat intake was 12 percent of daily calories. “A large proportion of the saturated fat Americans consume comes from animal proteins,” says Zhang. “These include red meats such as beef, pork, and lamb; processed meat such as sausages and bacons; and poultry with skin. Dairy foods such as butter, cream, whole milk, and cheese also contribute to saturated fat intake.” Protein from other sources like seafood, whole grains, nuts, and legumes remain a much smaller percentage.
“Although there is a moderate improvement in the diet quality of Americans over the past few decades, the progress that we have made has not yet brought us to where we need to be,” says Zhang. “These results provide insights into the priority areas that we should focus on to improve public health.”