Why is ultra-processed food so easy to overeat?

On ZOE Science & Nutrition ("Is ultra-processed food hiding in your fridge?", April 2023), doctor and Ultra-Processed People author Chris van Tulleken told host Jonathan Wolf why he doubted manufacturers could simply reformulate ultra-processed food into something healthier. Part of his answer, in that conversation, was about how the food feels in your mouth. Much of it is soft, and much of it is energy dense, with a lot of energy in each bite.

you consume calories quicker than essentially your hormone response can keep up and make you feel full.

Chris van Tulleken, ZOE Science & Nutrition, 2023

ZOE sells nutrition tests and products, so the show isn't neutral ground. This particular point, though, rests on research outside it.

The idea in plain words

Feeling full takes a little time. Your gut sends signals as food arrives, and they build over a meal. Food you can eat quickly, with little chewing, can get ahead of those signals. By the time you feel satisfied, you may have eaten more than you would have with a meal that slowed you down.

What the research says

The clearest test is Kevin Hall's 2019 trial at the US National Institutes of Health. Twenty adults lived in a clinic for four weeks: two weeks on ultra-processed meals, two on unprocessed ones, in random order. The meals offered were matched for calories, sugar, fat, salt and fiber, and people ate as much or as little as they liked. On the ultra-processed diet they ate more and gained weight. They also ate their meals faster, and those who sped up most tended to eat the most extra.

The authors are careful about why. The solid food on the ultra-processed diet was also more energy dense, and they write that the study wasn't designed to find the cause. Speed is a strong lead, then, rather than a proven explanation, and twenty people in a clinic for two weeks isn't everyday life.

A 2025 trial in London, the UPDATE trial, took the question closer to home. Fifty-five adults with a higher weight ate two diets for eight weeks each, both following the UK's healthy eating guide, one minimally processed and one ultra-processed, with the food delivered. Weight went down on both, and about twice as much on the minimally processed diet.

The good news hides in an older study. In a year-long trial, women told to add fruit and vegetables while cutting fat ate more food by weight than women who only cut fat. They reported feeling less hungry and lost a little more. Bulk that takes chewing seems to work with fullness instead of against it.

How this fits the Lose weight sustainably program

In the program's second paid chapter, "One day, from waking", you set a habit for your plate at lunch and dinner: about half vegetables or fruit, with some protein and whole grains, added around the foods you already eat. A short exercise, "Two labels, one choice", shows how to compare two similar packaged foods by one useful difference, such as more fiber or less sugar or salt, with no food banned. If your answers show no single obstacle, your starting point is adding a vegetable or fruit. See how Lose weight sustainably works; the first chapter is free.

Source: ZOE Science & Nutrition, "Is ultra-processed food hiding in your fridge?" with Chris van Tulleken and Tim Spector, 27 April 2023 Research: Hall et al, Ultra-processed diets cause excess calorie intake and weight gain (2019) · Dicken et al, UPDATE trial (2025) · Ello-Martin et al, Dietary energy density in the treatment of obesity (2007)