How Ultraprocessed Foods Hijack Metabolism and the Brain

Ultraprocessed foods have become the dominant source of calories in many countries, and the epidemiological case against them has grown steadily harder to ignore. A sweeping umbrella review of meta-analyses covering more than nine million people, published in the BMJ in 2024, linked ultraprocessed food exposure to a wide range of adverse health outcomes. Yet for all that observational weight, a fundamental question has remained stubbornly open: what actually happens inside the body and the brain in the minutes and hours after we eat these foods, before any chronic disease can develop? A new randomized, controlled, crossover study published in Nature Metabolism by Hutelin and colleagues takes aim at precisely that gap, characterizing the acute metabolic responses to ultraprocessed foods and probing how the brain encodes the value of what we consume, both in nutritional and in strictly monetary terms.

The framing of the new work draws heavily on a hypothesis articulated by Monteiro and colleagues in a 2025 review in The Lancet, which laid out the principal mechanisms by which ultraprocessed foods might damage health. Among the candidate explanations is the idea that these foods are not merely calorie-dense but are engineered in ways that interact with our metabolic and neural machinery in fundamentally distinct manners. The new study provides direct experimental support for that proposition, showing that the body’s immediate physiological reaction to an ultraprocessed meal differs measurably from its reaction to less-processed alternatives, and that these metabolic differences are mirrored in patterns of brain activity.

The experimental design matters here. Because the study was randomized, controlled and crossover, each participant experienced the different dietary conditions in varying orders, allowing the researchers to separate the effects of the foods themselves from individual differences in metabolism, preference or circumstance. That within-person comparison is the gold standard for questions of this kind, since metabolic responses to food vary enormously between individuals. By holding each person constant across conditions, the design isolates what the ultraprocessed foods themselves are doing to the body’s post-meal physiology.

What the researchers found is that ultraprocessed foods evoke a distinct metabolic signature. The acute responses that follow consumption, the cascade of hormonal and substrate changes that govern how the body processes an incoming meal, differ from those elicited by less-processed foods. This is a consequential finding because it shifts the debate away from a simple accounting of calories. Two meals with identical energy content may not be metabolically equivalent, and the new results suggest that the degree of processing, and not merely the macronutrient arithmetic on the label, shapes what the body does with the food it receives.

Equally striking is the neural half of the study. The investigators asked how the brain encodes food value, and they did so along two dimensions at once: the nutritional value of what is eaten and its monetary worth. This dual-axis approach reflects a growing recognition in the neuroscience of eating that the brain’s valuation systems do not treat food as a single undifferentiated reward. Instead, they integrate signals from multiple sources, including sensory input from the mouth and, crucially, post-ingestive signals rising from the gut that report on what the food is doing to the body’s metabolism once it has been swallowed.

That gut-to-brain framework was set out in a 2020 review by de Araujo, Schatzker and Small in the Annual Review of Psychology, which argued that food reward must be rethought to include the metabolic consequences of eating rather than taste alone. The new Nature Metabolism study operationalizes that idea. Its central figure shows a correlation between the brain’s response and the metabolic response to ultraprocessed foods, suggesting that the neural valuation of these foods is not independent of the body’s metabolic handling of them. In other words, what the gut tells the brain about a meal appears to be woven into how the brain values that meal.

There is important precedent for this kind of metabolic-neural coupling. A 2017 study published in Current Biology by Veldhuizen and colleagues demonstrated that the integration of sweet taste and metabolism determines carbohydrate reward, and that carbohydrate oxidation, the body’s actual burning of the sugar for fuel, was associated with neural activity in the nucleus accumbens, a key hub of the brain’s reward circuitry. That finding established that the brain’s reward regions are sensitive not just to the flavor of a carbohydrate but to its metabolic fate. The new study extends this logic into the ultraprocessed food domain, where engineered combinations of ingredients may produce especially potent metabolic signals for the brain to read.

Another strand of prior evidence concerns the notorious appeal of foods that combine fat and carbohydrate, a combination that whole foods rarely offer but that ultraprocessed products deliver routinely. Work by DiFeliceantonio and colleagues, published in Cell Metabolism in 2018, found supra-additive effects of combining fat and carbohydrate on food reward, meaning that the reward value of the combination exceeded the sum of its parts. That study also included observational findings supporting the idea that macronutrient composition influences how the brain encodes reward value independently of caloric load. The new results slot into this picture: ultraprocessed foods, with their carefully optimized macronutrient profiles, appear to engage neural valuation systems in a distinctive way, and that engagement tracks the metabolic response the foods provoke.

The significance of the work lies in how it connects the epidemiological and mechanistic levels of the ultraprocessed food debate. The large-scale observational studies can show associations between ultraprocessed food consumption and poor health, but they cannot by themselves explain why. Hypotheses have ranged from the energy density and hyperpalatability of these products to their additive and emulsifier content, to the speed with which they can be eaten. The new study contributes a piece of mechanistic evidence: the acute metabolic response to ultraprocessed foods is distinct, and that distinctiveness is visible in the brain’s response. This supports the hypothesis, outlined in the Lancet review, that the processing itself, through the metabolic and neural signals it generates, may be a driver of the health harms, rather than a mere bystander.

It is worth being precise about what the study does and does not establish. The findings concern acute responses, the short-term physiology and brain activity that follow consumption in a controlled experimental setting. Chronic disease outcomes, from obesity to cardiovascular disease, unfold over years and decades, and bridging the gap between a distinct post-meal metabolic signature and long-term health will require further work. The correlation between brain response and metabolic response reported in the study is just that, a correlation, and the direction of any causal influence between the two remains a question for future research. Nonetheless, the crossover design gives the acute findings unusual rigor, and the alignment of the results with a coherent pre-existing framework of gut-to-brain reward signalling gives them explanatory weight.

The broader implications reach into public health policy and food formulation alike. If the degree of processing changes the metabolic and neural conversation between gut and brain, then debates about food labeling, such as whether processing level deserves a place on nutrition panels alongside fat, sugar and salt, gain fresh scientific grounding. For the food industry, the results suggest that reformulation aimed solely at macronutrient targets may not neutralize the effects of processing if the engineered structure of the food itself drives distinct physiological responses. And for the millions of people trying to understand why ultraprocessed foods are so hard to stop eating, the study offers a compelling if sobering picture: these products may be speaking to the brain in a language that whole foods never use, a language written in metabolic signals that the brain’s reward circuitry has evolved to find irresistible. The new work, published as Hutelin and colleagues’ randomized, controlled, crossover study in Nature Metabolism, marks a step toward decoding that language, and with it, perhaps, toward designing foods and policies that work with our biology rather than against it.

Subject of Research: Acute metabolic and neural responses to ultraprocessed food consumption

Article Title: Ultraprocessed foods evoke distinct metabolic and neural responses

Article References: Ultraprocessed foods evoke distinct metabolic and neural responses. (2026). Nature Metabolism. https://doi.org/10.1038/s42255-026-01618-5

Image Credits: AI Generated

DOI: 10.1038/s42255-026-01618-5

Keywords: ultraprocessed foods, metabolism, food reward, gut-brain signalling, nucleus accumbens, nutrition, neuroscience, food processing, public health, crossover study, Nature Metabolism, macronutrients