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Preventive Medicine: Ultraprocessed food makes us fat — who knew?



Ultraprocessed foods make us overeat, and get fat. Who knew?

Dr. Kevin Hall and colleagues at the NIH conducted the first ever randomized controlled trial that specifically isolated the effects of ultraprocessing of food on energy balance, weight, and many other aspects of metabolism beyond the scope of this column. Ultraprocessed food was defined for the study using a classification called NOVA, developed by Professor Carlos Monteiro and colleagues. For our purposes, ultraprocessed food is likely familiar as “junk,” and something most of us would recognize when we see it. Such foods contain industrially processed ingredients, and often many chemical components not native to any actual food found in nature.


Twenty adults, ten men and ten women, whose weight had been stable before the study, were admitted to the metabolic ward at the NIH for a month. The importance of such a facility can scarcely be overstated; it removes any and all potential guesswork from the assessment of dietary intake, calories consumed, and calories expended. Study participants were in a completely controlled environment for the full span of the trial, their dietary intake was captured accurately and completely, and intermittently throughout the study their energy expenditure was measured precisely in a respiratory chamber. Each participant was randomized to a sequence of ultraprocessed versus minimally processed foods, and each study phase lasted two weeks. Such a trial is called a “crossover,” and by allowing each study participant to serve directly as her/his own control, adds greatly to the minimization of potential noise in the data.


The resulting signal was perfectly clear. The ultraprocessed foods led directly to overconsumption of roughly 500 calories daily, and weight gain highly correlated with those calories. Though not a primary focus of this trial, that strong correlation between calories and weight nonetheless, and once again, affirms — despite misguided noise to the contrary — that calories, indeed, do count. However, this study also demonstrated emphatically why counting calories, per se, is not the best way to control their intake. For that, focus on the quality of foods.

The investigators matched the two diets for many key elements of nutrition, including calories, energy density, macronutrients (fat, carbohydrate, and protein), sugar, sodium, and fiber. In the real world, however, such nutrients are widely divergent between minimally processed and ultraprocessed foods. In particular, high concentrations of added sugar and salt, and low fiber content, are characteristic of “junk food,” and almost certainly contribute to the effects of such foods on total intake. As the investigators themselves noted: “Had the experimental diets used in our study allowed for greater differences in sugar, fat, and sodium content more typical of differences between ultraprocessed versus unprocessed diets, we may have observed larger differences in energy intake.” They, judiciously, say “may have;” I say, undoubtedly would have.


So, the real-world effects of ultraprocessed junk foods on overconsumption are almost certainly greater than this study demonstrates. Be that as it may, and even despite the strict methodologic proprieties of this research team, we now have proof that ultraprocessed food leads directly to overeating, and weight gain. That is an important milestone, and one that rightly resulted in widespread media attention to the study.

We have, however, long had ample warning of this probability, and reason to suspect that data perhaps this robust or nearly so were locked away in the vaults of Big Food. In 2005 and 2006, the Chicago Tribune ran a four-part exposé on food processing based on documents secured under subpoena of the tobacco industry. The coverage concluded that tobacco and food industry scientists were collaborating, and sharing functional MRI machines, to study how best to stimulate addictive pathways in the human brain. We received much the same message again a decade later, expertly delivered by Pulitzer Prize winner Michael Moss, both in his book — and prominently as a New York Times Magazine cover story.

With the proof of such effects now revealed to us all, there is one vital question the randomized trial cannot answer: what are we going to do about it?


Dr. David L. Katz author, The Truth about Food

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