Last Updated & Content Validated On: Nov 13, 2025
You’re Eating 500 Extra Calories Every Day Because of This Common Habit
First Published: Nov 13, 2025
We all know ultra-processed foods aren’t great for us — but an NIH study shows just how powerfully they can influence our appetite.
In a controlled trial, researchers found that people eating an ultra-processed diet consumed about 500 more calories per day than when eating an unprocessed diet — even though both meal plans contained the same amount of sugar, fat, and nutrients.
Over just two weeks, participants gained nearly 2 pounds on the ultra-processed diet — and lost the same amount when eating unprocessed foods.
When Processed Means “Hard to Stop Eating”
The study, conducted at the NIH Clinical Center, followed 20 adults who lived in the research facility for a month. For two weeks, they ate a diet made up of ultra-processed foods — think packaged breads, cereals, frozen meals, and “healthy” snack bars. Then, they switched to a minimally processed diet of whole grains, fresh fruits, vegetables, and lean proteins.
Each diet was designed to be nutritionally identical: matched for calories, sugar, fat, sodium, and fiber. Participants could eat as much or as little as they wanted — no calorie limits, no restrictions.
The results were striking:
🍟 On the ultra-processed diet, participants ate ~500 extra calories per day — mostly from carbs and fat.
🥗 On the unprocessed diet, they naturally ate less without trying.
Weight changes closely tracked these differences in intake:
+2 lbs on the ultra-processed plan,
−2 lbs on the unprocessed one.
Why It Happens
the difference isn’t just about nutrition — it’s about how the food feels and how fast we eat it.
Ultra-processed foods tend to be:
- Softer and faster to chew — letting us eat more before feeling full.
- High in fat, sugar, and salt — a combination that keeps the brain craving more.
- Low in fullness signals — they digest quickly, leaving us hungrier sooner.
In short, these foods are engineered for overconsumption.
What Counts as “Ultra-Processed”?
Ultra-processed foods go beyond simple cooking or preservation. They often include industrial ingredients such as:
- Flavor enhancers, colorings, or emulsifiers
- Added sugars and refined starches
- Ingredients you wouldn’t use in your own kitchen
Common examples include:
- Sweetened cereals
- Energy or protein bars
- Packaged breads
- Instant noodles
- Flavored yogurts
- Frozen entrees
If the ingredient list reads more like a chemistry set than a recipe — it’s ultra-processed.
How to Eat Less — Without Thinking About It
You don’t need to count every calorie to reap the benefits seen in the study. The key is to nudge your diet toward less processing.
✅ Choose foods with short ingredient lists.
✅ Base your meals on whole or minimally processed foods — fruits, vegetables, beans, whole grains, and lean proteins.
✅ Watch out for “healthy” snacks — even high-protein or low-sugar versions can still be ultra-processed.
✅ Cook more often. Even simple home-cooked meals reduce exposure to highly engineered foods.
Small shifts can reset your appetite and help your body’s natural hunger signals work again.
The Bottom Line
This NIH trial offers rare, controlled evidence that ultra-processed foods can make us overeat — without realizing it.
Even when matched for nutrients, these foods led participants to eat hundreds of extra calories a day and gain weight in just two weeks.
The takeaway is simple but powerful:
If you can’t recognize the ingredients, your body probably can’t either.
Reference(s)
[1] Hall, K. D., Ayuketah, A., Brychta, R., Cai, H., Cassimatis, T., Chen, K. Y., Chung, S. T., Costa, E., Courville, A., Darcey, V., Fletcher, L. A., Forde, C. G., Gharib, A. M., Guo, J., Howard, R., Joseph, P. V., McGehee, S., Ouwerkerk, R., Raisinger, K., Rozga, I., … Zhou, M. (2019). Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell metabolism, 30(1), 67–77.e3. https://doi.org/10.1016/j.cmet.2019.05.008
