For decades, NIH had awarded special grants to teaching hospitals and academic institutions so these research centers could hire trained staff like nurses and dieticians, and maintain beds for participants in clinical trials. These centers conducted rigorous, highly controlled feeding studies and other research that profit-driven industries like drug or food manufacturing wouldn’t benefit from funding. They also attracted young researchers who didn’t have enough resources to recruit and pay staff or rent out a facility.

“There are certain kinds of research that is done nowhere else, like nutritional research,” said David Nathan, director of the clinical research and diabetes centers at Massachusetts General Hospital and a professor at Harvard Medical School. “Pharma doesn’t support that because there is no drug to be sold.”

Before the elimination of these clinical research center grants, Mario Kratz, an associate professor in epidemiology and medicine at the University of Washington, said he could conduct a well-controlled dietary intervention study in which all food was provided to participants over four months for about $12 a day per person. Now, because he has to pay for the facility and research staff salaries, the cost has shot up tenfold.

Theoretically, investigators could request this higher amount from NIH directly to pay for a specific research project. However, most NIH grants are effectively capped at $500,000 — a threshold that has not increased in a decade — and are no longer sufficient to cover the costs of most clinical feeding studies.

“It has made it impossible for me and my colleagues to propose these types of studies,” said Kratz, who also works at the Fred Hutchinson Cancer Research Center in Seattle, where he studies dietary interventions and cancer prevention. “It’s now cost-prohibitive. I think nutrition feeding studies were an unintended casualty.”

Clinical nutrition research faced another potential blow earlier this year. NIH leadership in May proposed closing the only metabolic research unit at NIH headquarters in Bethesda, Md. The unit that was on the chopping block has a kitchen for preparing and measuring meals, private rooms where people can stay overnight for extended periods of time and be observed, as well as specially trained research staff, including nurses who prevent people from smuggling food in or out of patient’s rooms — a crucial role, considering high-calorie contraband could throw off a study’s results.

It housed a recent high-profile clinical trial that was the first to demonstrate a cause-and-effect relationship between ultraprocessed foods and weight gain. For the study, published in the journal Cell Metabolism in May, researchers designed two diets that had the same levels of calories, carbs, fat and protein. The only significant difference was whether the foods were unprocessed or considered ultraprocessed: spinach salads with chicken, apples, bulgur and homemade dressing were designated the former; foods like canned ravioli and white bread were the latter.

The participants had no underlying health problems and were randomly assigned to one of the diets for the first half of the study, and to the other for the second half. The study was a month long and levels of exercise were held constant.

The results were a breakthrough: Those on the ultraprocessed foods diet on average ate 500 more calories each day, causing weight gain, compared with those eating unprocessed food, who lost weight on average. Previous research looking at this question had shown that processed food was associated with weight gain, but this study showed definitely that processed food caused weight gain.

Around the same time the landmark study was published, NIH proposed closing its metabolic research unit, sparking pushback from the scientific community. In a letter to the agency’s leadership in June, the American Society for Nutrition and The Obesity Society argued the closure would imperil important research. The proposal “indicates that nutrition research is not considered a prominent area of scientific pursuit at NIH,” ASN wrote.

NIH said there is no “current plan” to close the research unit.

“There has been discussion about relocating the capabilities of this unit,” the agency said in a statement. “This would require a great deal of additional planning, communication, and coordination to ensure that the important research done there would not be adversely affected.”

Kevin Hall, an intramural researcher at NIH focused on nutrition and obesity — and the lead author of the ultraprocessed food study — said in an interview that the agency in 2017 also shrunk the number of beds in the metabolic ward from 10 to seven to make room for other research.

NIH has just one other similar metabolic facility at a branch in Phoenix, which studies determinants for obesity and diabetes. That facility has 15 beds.

Having fewer beds means it takes researchers much longer to run such highly controlled trials, because they have to stagger their overnight patients. Hall’s processed food trial, for example, took roughly eight months to complete, even though it included only 20 participants.

Hall thinks the nutrition field needs more of these in-patient trials to settle some of the thorniest debates over nutrition. Otherwise, researchers don’t know with certainty what people actually ate, he said.

"You're not studying the diet at all,” Hall said. “You're studying the effect of the advice.”

BY THE TURN of the 20th century, the Department of Agriculture had begun exploring how proper nourishment could help both farmers and an increasingly urban population. Nutritionists identified milk and fruits and vegetables — at the time luxury products — as “protective foods” for good health. They made great strides in understanding vitamin deficiencies, helping to largely eliminate diseases like rickets, scurvy and pellagra in the United States by World War II.

Still, by 1940, with the looming possibility of America’s entry into the war, 40 percent of recruits were deemed unfit to serve because they were underweight or malnourished. President Franklin D. Roosevelt convened an emergency conference that led to the first federal diet recommendations and an expansion of USDA’s school lunch program and food stamps, now known as the Supplemental Nutrition Assistance Program.

Nutrition wasn’t thrust into the national spotlight again until the late 1960s and 1970s, after a CBS News special on hunger in America raised alarm. Sen. George McGovern, a Democrat from South Dakota, formed a special committee to respond to the large number of poor people who were malnourished. The Nixon administration exactly 50 years ago this winter also organized a White House conference to “lay the foundation of national nutrition policy based on need, not agricultural subsidies,” wrote one organizer.