The content of the upcoming Dietary Guidelines for Americans could hinge on findings of a renowned – but subsequently controversial – American scientist who concluded that overconsumption of saturated fats leads to heart disease.
Ancel Keys was a physiologist who conceived what’s known as the Seven Countries Study, in which he examined diets of people in the U.S., Finland, Italy, Greece, the former Yugoslavia and Japan. His work includes books published in 1959 and 1975, the second of which was titled “The Mediterranean Way” and advocated a diet that favored plant foods over animal foods, “whole grains products rich in fiber, [and] a large intake of all kinds of vegetables,” according to a 2025 scientific review of his work published in the Journal of Cardiovascular Development Disease.
In addition, Keys recommended “meat … consumed with moderation, with an emphasis on excluding red and fatty meats in favor of poultry,” regular consumption of fish and seafood, and moderate intake of milk, “with a preference for skim milk and low-fat dairy products.”
There’s more: “Olive oil should be the major dressing and cooking fat, while other hard fats should be excluded; sugar, sugar products, and pastries should be limited to maintain a low glycemic index; and alcohol intake should be moderate, preferable with small amounts of red wine,” the review summarized.
Keys’ work received widespread attention – he even made the cover of Time magazine in 1961 – and his linking of saturated fats consumption to cardiovascular disease (CVD) appears to have stood the test of time, according to studies conducted since Keys’ original work was published decades ago, Jerry Mande, CEO of Nourish Science and an adjunct professor of nutrition at Harvard T.H. Chan School of Public Health, told Agri-Pulse.
However, Keys’ research has been under attack in recent years by journalists and some researchers, who say he “cherry-picked” the countries he studied to confirm his hypothesis and made other mistakes in his research that ended up singling out fat unfairly.
At a recent USDA event touting ice cream makers’ commitment to phase out artificial food colors, Food and Drug Administration Commissioner Marty Makary criticized Keys, who died in 2004 at the age of 100.
Marty Makary (AP photo) “Ancel Keys in the 1960s decided to demonize saturated fat with a hypothesis that was supported with data that was incomplete and methodologically flawed in his Seven Countries Study,” Makary said.Makary went on to say that despite a “robust debate” in the medical establishment, that same establishment ended up embracing “groupthink” before they “locked arms and walked off a cliff together, insisting that the reason for heart disease in the United States was that people were not eating skim milk and no-fat and low-fat foods, ignoring the roles of refined carbohydrates and so many other things that drive general body inflammation, which is the precursor of fat deposition in the arteries.”
“That dogma still lives large, and you see remnants of it in the [dietary] guidelines that we are now revising,” which Makary said will be “based on science and not medical dogma.”
Secretary of Health and Human Services Robert F. Kennedy Jr. backed Makary, saying at the July 14 press conference that “there’s a tremendous amount of emerging science that talks about the need for more protein and more fats in our diet, and there’s no industry that does this better than [the dairy] industry,” he said, promising to “elevate” whole milk, cheese and yogurt in the upcoming guidelines, which he said would be out in “the next several months.”
The current 2020-2025 guidelines continue a longstanding recommendation that Americans not get more than 10% of their calories from saturated fats. The latest scientific report completed by the 2025-2030 Dietary Guidelines Advisory Committee would keep that recommendation.
Its scientific report, which was sent to Secretary of Agriculture Brooke Rollins and Kennedy to help craft the final guidelines, says the previous committee’s review “demonstrates that replacing saturated fat with unsaturated fats, especially [polyunsaturated fats (PUFA)], in adults significantly reduces” both total cholesterol and LDL-C cholesterol – so-called “bad cholesterol.”
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That review also concluded that “strong evidence demonstrates that replacing saturated fat with PUFA in adults reduces the incidence of coronary heart disease events and cardiovascular disease mortality.” Limited evidence, however, was available to determine whether replacing saturated fatty acids with mono-unsaturated fats “confers overall cardiovascular disease endpoint health benefits.”
Jerold Mande (Tufts photo)Sat fats and total fats get 'conflated'
Mande said Makary and other critics of Keys tend to “conflate” saturated fat with total fat.
“Keys’ focus on saturated fat seemed to morph into a broader indictment of fat,” Mande said, citing as an example the Nutrition Facts label that he was involved in designing, which lists “total fat” at the top before providing Daily Value percentages for saturated fat and trans fat.
“It really shouldn’t be there,” Mande said of the “total fat” information.
“Keys really focused on the role of saturated fat and cardiovascular disease (CVD),” Mande said, offering some historical context. When Keys began his work, the incidence of CVD “was much worse,” Mande said. He "operated at a point in time where you had these raging epidemics, and we were looking to understand the cause of it,” he said.
While CVD continues to be the leading cause of death for adults in the U.S., mortality from heart disease declined 66% from 1970 to 2022, and heart attacks have fallen by nearly 90%, according to an American Heart Association analysis of data from the Centers for Disease Control and Prevention.
Mande said other factors have also come into play: the introduction of cholesterol-reducing drugs, a sharp decrease in smoking and the discovery of trans fats, which have been “eliminated from our food altogether.”
There also are “personalized” factors that have contributed to a “more nuanced” view of saturated fats, he said.
“It's not that Keys was wrong, but we've learned a lot more about it,” he said. “A big piece is, what is your risk of cardiovascular disease? Do you have a history of high cholesterol leading to cardiovascular disease in your family and shorter lives as a result, or illness as a result? It's really important to manage your blood cholesterol.”
Marion Nestle, a nutritionist and author of the book Food Politics, also defends Keys. “To me, Ancel Keys is a great hero,” she told geophysicist Chris MacAskill, a proponent of plant-based diets. “He was an extraordinary researcher who did first-rate work in a number of fields.”
Others have called criticisms of Keys unfounded. A white paper by the True Health Initiative, "a global coalition of experts from over 50 countries, united to combat misinformation and disinformation that impact public, personal, and planetary health," says flatly, "Allegations suggesting that [Seven Countries Study (SCS)] researchers chose locations where they already knew the outcomes are clearly false based on review of primary source material, the relevant timelines, and direct questioning of investigators."
That paper also said that "studies conducted by Keys and his SCS colleagues did reveal an association between sugar intake and cardiovascular disease, albeit a weaker one than for dietary sources of saturated fat. However, "Nothing in this body of work ever encouraged or justified the substitution of added sugar for saturated fat, and Keys was never an advocate for any such thing. There is more than one way to eat badly, and if the American public has been committed to exploring them sequentially, blame for it cannot be laid at the door — or now the grave — of Ancel Keys."
RFK Jr. and Rollins urged to follow the science in DGAs
Dozens of health and environmental groups urged the RFK Jr. and Rollins last month to “follow the science” in writing the dietary guidelines. In a letter led by the Center for Science in the Public Interest, they said the DGA has “been consistent in its recommendation to limit saturated fat, commonly found in higher amounts in high-fat meat, full-fat dairy products and butter.
“The scientific consensus remains clear: Saturated fat is consistently linked with increased risk of cardiovascular disease, and replacing saturated fat with unsaturated fats, particularly polyunsaturated fats, has well-documented benefits for cardiovascular health,” they said.
Jessi Silverman, campaign manager for institutional food purchasing and service at CSPI, says “it seems like we can expect some change to the advice and weakening of recommendations around limiting saturated fat and or potentially exempting dairy specifically from recommendations to limit saturated fat intake.”
“We are very concerned about the policy implications of weakening saturated fat recommendations,” she says. “If school meals, for example, were allowed to contain more saturated fat, that has negative implications for the health of children who rely on those meals.”
The dietary guidelines are used to develop meals served in public schools.
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