The evidence against “ultra-processed” foods is weaker than you think |
The evidence against “ultra-processed” foods is weaker than you think
New analysis suggests other factors may explain the harms blamed on “ultra-processing.”
In little more than a decade, the term “ultra-processed foods” (UPFs) has risen from an obscure academic coinage to one of the most potent ideas in the American food imagination. It has saturated media coverage of diet and disease, spawned a profusion of guides teaching shoppers how to spot UPFs at the supermarket, and animated Robert F. Kennedy Jr.’s crusade to remake American food policy.
It might also be kind of fake.
The trouble starts with the definition. UPF generally refers to packaged foods with questionable-sounding ingredients not typically used in household kitchens (high-fructose corn syrup, maltodextrin, and the like). But not even nutrition scientists can really tell you where normal processing ends and “ultra-processing” begins, and the difference often comes down to vibes. (I once covered a study that, inexplicably, classified tofu as ultra-processed.)
Further, much of the evidence linking ultra-processed foods to poor health outcomes such as heart disease and cancer is notoriously low-quality because it’s based on big, noisy observational studies that can’t disentangle correlation from causation. That weakness plagues a lot of nutrition research, but it’s especially notable for UPF studies, because many of them are drawn from diet surveys that don’t capture enough detail to tell whether the “white bread” or “yogurt” someone reported eating was ultra-processed in the first place.
To correct for those problems, a handful of nutrition researchers have run randomized controlled trials (RCTs) — a gold standard for establishing cause and effect — to isolate the health effects of “ultra-processed” foods. Several of the best-known trials have found that UPFs indeed do contribute to adverse health outcomes such as overeating and weight gain — seemingly offering the stronger evidence that observational studies could not.
But it turns out those trials might not show what they claim to, either. In a recent article published in Science, a group of researchers analyzed data from five landmark randomized controlled trials of ultra-processed foods and found that most of them compared ultra-processed and non-ultra-processed diets that differed in important ways beyond processing. The ultra-processed diets tended to be more calorie-dense and lower in fiber, for example, which can lead to overeating regardless of whether a food is “ultra-processed.” Accordingly, some of the effects that they attributed to processing may have had other causes.
These findings matter well beyond an academic fight over food categories. They offer the latest evidence against taking the UPF label too seriously when deciding what to buy — or fear — at the grocery store.
Randomized controlled trials sought to add clarity to the UPF debate
UPF researchers sort foods using NOVA, a classification system with four tiers. From least to most processed:
Group one includes unprocessed or minimally processed foods, like whole fruits, vegetables, whole grains, beans, nuts, milk, and cuts of meat.
Group two encompasses “processed culinary ingredients,” like cooking oils, butter, sugar, and salt.
Group three is made up of processed foods produced by combining group one and group two ingredients into things like homemade breads, desserts, sautés, cured meats, and other dishes.
Group four, or ultra-processed foods, is defined as “formulations of ingredients, mostly of exclusive industrial use, that result from a series of industrial processes,” including dyes,........