Harvard flags contradictions in US dietary fat guidelines

Beef tallow, butter and cheese — animal-based foods high in saturated fat — have been given prominent placement in the United States' new dietary guidelines food pyramid. The arrangement gives the impression that limits on saturated fat have been dropped. In fact, the actual guidelines retain the longstanding rule that saturated fat should account for no more than 10 percent of total daily calories.

Nutrition researchers at Harvard T.H. Chan School of Public Health were quick to flag the discrepancy. The school is widely recognized as a global authority in nutrition research. According to its nutrition information website, Frank Hu, a nutrition professor at Harvard T.H. Chan School of Public Health, said the pyramid "sends contradictory messages about how much saturated fat-rich food to eat," adding that "this confusion could lead to higher saturated fat intake, raising LDL cholesterol levels and increasing the risk of cardiovascular disease."

The concern is that the food pyramid groups animal-based foods high in saturated fat — such as meat and dairy — alongside plant-based foods that are low in saturated fat, creating confusion. The pyramid also offers no guidance on how often or how sparingly each food should be eaten to stay within recommended limits.

Harvard researchers also illustrated the practical problems that can arise when applying the new guidelines day to day. For a 2,000-calorie diet, the 10 percent saturated fat cap works out to roughly 22 grams. The new guidelines recommend three daily servings of dairy for a 2,000-calorie diet — for example, one cup of milk, three-quarters of a cup of Greek yogurt and about 28 grams of cheddar cheese. Eating all three together already adds up to 17 grams of saturated fat.

Adding just one tablespoon of butter or beef tallow — both listed in the guidelines as cooking fats — tacks on another 6 to 7 grams of saturated fat, pushing intake past the daily limit. That figure does not even account for the saturated fat found in other foods such as protein sources. Following the combination of foods the new guidelines recommend makes it easy to exceed the saturated fat cap, the researchers said.

Harvard T.H. Chan School of Public Health said "the most important thing about the fat we eat is the type of fat," adding that "reducing saturated fat intake and replacing it with healthy unsaturated fats is the healthier approach."

The Harvard researchers also took issue with the WHO's 2023 dietary guidelines on fat intake, which recommend that adults limit total fat consumption to no more than 30 percent of total calories.

Harvard nutrition experts disagree with that recommendation, saying there is no confirmed evidence that a low-fat diet reduces the risk of chronic disease or aids in weight loss.

A large-scale Spanish clinical trial published in the New England Journal of Medicine in 2018 found that a Mediterranean diet group — whose members derived 39 to 42 percent of their total calories primarily from unsaturated fats — had lower risks of cardiovascular disease and type 2 diabetes than a low-fat diet group. The Mediterranean diet group exceeded WHO's total fat intake recommendation, yet its health indicators came out higher.

Harvard nutrition researchers said they agree with the WHO guideline recommending unsaturated plant-based fats over saturated and trans fats, but said a blanket cap of 30 percent of total calories on all fat is not appropriate. Rather than focusing solely on cutting the quantity of fat consumed, they said, the type of fat eaten deserves greater consideration.