Ultra-Processed Foods: The Trial That Measured 500 Extra kcal per Day
Exercise professional · creator of the Letz method
Short answer
In a controlled inpatient trial with diets matched for offered calories, macronutrients, sugar, sodium, and dietary fiber, participants spontaneously consumed approximately 500 kcal more per day during the ultra-processed phase and gained weight, whereas they lost weight during the minimally processed phase.
Why this study is different
Almost everything known about ultra-processed foods comes from observational studies, where individuals who eat more of these foods also differ in income, education, and physical activity levels. That design cannot separate diet from the rest of life.
The study in question took place in a controlled inpatient setting, with both diets matched for offered calories, macronutrients, sugar, sodium, and fiber. Participants ate ad libitum. The only meaningful difference was the degree of food processing.
The findings
During the ultra-processed phase, spontaneous intake was roughly 500 kcal per day higher. Participants gained weight in that phase and lost weight in the other, without anyone instructing them to eat more or less.
The key takeaway is not that ultra-processed foods cause weight gain through some magical property. Rather, they lead people to eat more without realizing it—a distinct problem that is much harder to solve through willpower alone.
The likely mechanism
Two related variables help explain this effect: energy density and eating rate. Foods that require less chewing are eaten faster, and eating faster increases the amount consumed before satiety sets in.
Protein and foods that require chewing increase satiety for the same amount of energy—providing a practical lever that does not depend on tracking anything.
Frequently asked questions
Do ultra-processed foods cause weight gain on their own?
The controlled trial shows that they lead people to eat more spontaneously—roughly 500 kcal per day more with matched macronutrients. Weight gain stems from this higher caloric intake, not from an isolated metabolic property.
Do I need to cut out ultra-processed foods completely?
The adherence literature suggests that all-or-nothing approaches usually fail. The finding is about overall dietary proportion, not outright prohibition.
Does eating slowly actually help?
Yes. Eating rate influences the amount consumed before satiety sets in, making it a practical lever that does not require counting calories.
Registry rules cited here
- Ultra-Processed Foods Lead to Eating MoreWhen meals were matched for macronutrients, an ultra-processed diet led participants to eat roughly 500 kcal more per day and gain weight.
- Satiety: Protein and Eating SpeedHigher-protein diets reduce appetite and spontaneous intake; eating more slowly reduces the amount consumed in a meal.
- Fiber and Carbohydrate QualityConsuming 25 to 29 g of fiber per day, alongside whole grains, is associated with lower mortality and fewer cardiometabolic diseases.
- Diet Type Matters Less Than AdherencePopular named diets lead to similar weight loss; adherence to the plan predicts outcomes far more than the ratio of carbohydrates to fat.
Sources cited
- Hall et al., Cell Metabolism, 2019 DOI 10.1016/j.cmet.2019.05.008
- Weigle et al., American Journal of Clinical Nutrition, 2005 DOI 10.1093/ajcn.82.1.41
- Robinson et al., American Journal of Clinical Nutrition, 2014 DOI 10.3945/ajcn.113.081745
- Reynolds et al., The Lancet, 2019 DOI 10.1016/S0140-6736(18)31809-9
- Johnston et al., JAMA, 2014 DOI 10.1001/jama.2014.10397
- Gardner et al., JAMA, 2018 DOI 10.1001/jama.2018.0245
- Alhassan et al., International Journal of Obesity, 2008 DOI 10.1038/ijo.2008.8
Informational content about training and nutrition. It is not a recommendation, prescription or adjustment of any medication, and it does not replace assessment by your doctor or dietitian.