Research debates whether ultra-processed foods are addictive or engineered for overconsumption

A symposium at McGill explores conflicting views on whether ultra-processed foods are inherently addictive or simply designed to encourage overconsumption, with implications for tackling obesity.

At a recent McGill Office for Science and Society symposium, two leading researchers offered sharply different explanations for why ultra-processed foods are so closely linked with overeating and weight gain. Ashley Gearhardt, a psychologist at the University of Michigan who created the Yale Food Addiction Scale, argued that these foods can behave like addictive substances. Kevin Hall, a senior scientist at AstraZeneca and incoming chair at the University of Ottawa, said the evidence points instead to the way certain foods are engineered to be easy to overconsume, especially when they are energy-dense and highly palatable.

Gearhardt framed the issue through the language of addiction, drawing comparisons with the history of tobacco and other substance-use disorders. She pointed to research using the Yale Food Addiction Scale suggesting that a meaningful share of adults and children show addiction-like eating patterns, with even higher rates in clinical populations. Her case rested on the idea that modern food products often combine refined carbohydrates and fats in ways rarely found in nature, creating strong reinforcement and making some people especially vulnerable to compulsive consumption.

Hall approached the question from a different angle, focusing on human energy balance. He said the body reacts to weight loss with a two-pronged biological response: metabolism slows and appetite rises, which makes sustained weight reduction difficult. He also revisited his widely discussed 2019 inpatient trial, which found that people eating an ultra-processed diet consumed about 500 calories more per day than when they ate an unprocessed diet matched for nutrients, and gained more weight as a result.

More recent findings presented in the symposium complicated the addiction narrative. Hall described a PET imaging study in which an ultra-processed milkshake did not produce the kind of measurable dopamine surge in the striatum that would be expected if these foods acted like classic drugs of abuse. He also cited a four-diet inpatient crossover trial in which an ultra-processed diet was reformulated to be lower in energy density and less reliant on hyper-palatable combinations of fat, sugar and starch. In that setting, participants spontaneously ate less and lost weight, despite the food still qualifying as ultra-processed by classification.

Taken together, the discussion suggested that ultra-processed foods may not be harmful because of processing alone, but because many are designed to be energy-dense, easy to eat quickly and unusually rewarding. Supporting that view, recent studies indexed in PubMed and ScienceDirect have reported that sodium, fat and starchy carbohydrates can all increase how reinforcing foods feel, while long-term U.S. data show rising consumption of ultra-processed, hyper-palatable and high-energy-dense foods alongside worsening obesity trends. For parents and caregivers, the practical message is less about banning categories than about reducing the kinds of foods most likely to drive passive overeating: prioritising lower-energy-dense meals, cutting liquid sugar, and relying more on fibre-rich whole foods may make a meaningful difference.