food tracks with obesity in survey after survey, and surveys cannot separate the processing from everything that travels with it. The way to isolate it is to match the two diets on everything else and let people eat freely. So 20 adults moved into a research ward and ate each diet for two weeks, with meals matched for calories offered, , , sugar, sodium and fiber. Did intake differ?
They ate 508 calories a day more on the processed diet. The excess came from carbohydrate, about 280 calories a day, and fat, about 230, with protein intake unchanged. Weight followed intake closely, and participants gained 0.9 kilograms over the two ultra-processed weeks and lost 0.9 kilograms over the unprocessed ones. Same person, same offered calories, opposite direction.
Ultra-processed food is associated with obesity across large populations, and association is as far as that evidence goes. People who eat more of it differ in income, cooking time, sleep and much else, and the food itself differs in sugar, salt, fat and fiber. Isolating processing means holding all of that still.
Twenty , mean age 31 years and mean body-mass index 27, were admitted to the NIH Clinical Center. Each was randomized to receive either an ultra-processed or an unprocessed diet for two weeks, then the other diet for two weeks. The meals were designed to match on presented calories, energy density, macronutrients, sugar, sodium and fiber. Participants were told to eat as much or as little as they wanted.
Energy intake was 508 calories a day greater on the ultra-processed diet. The surplus came from carbohydrate, up about 280 calories a day, and fat, up about 230, while protein intake did not shift at all. So the extra eating was not spread evenly across the diet.
Weight changes tracked intake closely, with a correlation of 0.8. Participants gained 0.9 kilograms during the ultra-processed fortnight and lost 0.9 kilograms during the unprocessed one. The authors suggest limiting ultra-processed food may be an effective strategy for preventing and treating obesity. Weigh the setting too: twenty people, a metabolic ward, two weeks an arm, and food they did not shop for or cook.
wat. Offered matched meals and told to eat freely, the same people took in five hundred extra calories a day on the processed menu.
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It turns a correlation into a cause under controlled conditions. Matching the nutrients and still finding a five-hundred-calorie gap points at something about the food’s form rather than its composition.
How do we know?
Hall and colleagues admitted 20 weight-stable adults to the NIH Clinical Center and randomized the order of two matched two-week diets, ultra-processed and unprocessed. Participants were told to eat as much or as little as they wanted.
What is still unknown
Twenty people, two weeks per arm, living in a research ward and eating only what was provided, which is not how anybody eats. A crossover this small establishes the effect without telling you its size in ordinary life.
Learn something?
Where to next
Can teaching new parents to read a baby’s cues change the child’s weight at three?satiety