BRISTOL, UK, February 29, 2024 — Forget calorie counting. A surprising new analysis reveals that people naturally eat 57% more food by *weight* when consuming a completely unprocessed diet, yet still consume an average of 330 fewer calories per day. This challenges the long-held belief that overeating is the primary driver of weight gain.
The Power of Whole Foods
Table of Contents
A shift to whole, unprocessed foods can lead to reduced calorie intake despite larger portion sizes.
- People on unprocessed diets ate significantly more food by weight than those on ultra-processed diets.
- Despite eating more, those consuming whole foods consumed fewer calories daily.
- The nutritional makeup of food influences choices, with ultra-processed foods potentially encouraging higher calorie consumption.
- Participants on whole food diets intuitively selected foods that balanced nutrition and fullness.
The original 2019 clinical trial, led by Kevin Hall, Ph.D., then at the National Institute of Health, first demonstrated that an exclusive diet of ultra-processed foods (UPFs) led to excessive calorie intake and weight gain. This reanalysis, published in The American Journal of Clinical Nutrition, digs deeper into *why*.
Participants who ate only whole foods consistently consumed more fruits and vegetables—sometimes several hundred grams per meal—instead of calorie-dense options like steak, pasta, and cream. “Overeating is not necessarily the core problem,” explains lead author Jeff Brunstrom, professor of Experimental Psychology at the University of Bristol, UK. “Our research clearly demonstrated that consumers on a whole food diet actually ate far more than those on a processed food one. But the nutritional make-up of food is influencing choices, and it seems that UPFs are nudging people toward higher calorie options, which even in much lower quantities are likely to result in excess energy intake and in turn fuel obesity.”
Participants on the whole food diet consumed more fruit and vegetables, resulting in higher food but lower calorie intake.
Diet Quality Matters
The analysis also revealed a significant difference in nutritional quality. Participants on whole food diets benefited from a wider range and greater volume of essential vitamins and minerals found abundantly in fruits and vegetables. “Had participants eaten only the calorie-rich foods, our findings showed they would have fallen short on several essential vitamins and minerals and eventually developed micronutrient insufficiencies,” explains study co-author Mark Schatzker, at McGill University, Canada. “Those micronutrient gaps were filled by lower-calorie fruits and vegetables.”
Interestingly, the authors note that individuals consuming only UPFs could also meet their micronutrient needs, as these foods are often fortified with vitamins. However, this doesn’t negate the benefits of obtaining nutrients from whole, natural sources.
UPFs vs. Unprocessed: A Closer Look
In the 2019 trial, 20 weight-stable adults were assigned to either an ultra-processed or unprocessed diet for two weeks, then switched to the alternate diet for another two weeks. Researchers meticulously matched meals for calories, energy density, macronutrients, sugar, sodium, and fiber, allowing participants to eat as much or as little as they desired.
Those on the UPF diet consumed an average of 508 more calories daily, with increases in carbohydrate (280 kcal) and fat (230 kcal) intake, while protein intake remained similar. Consequently, participants gained an average of 0.9 kg on the UPF diet, but *lost* 0.9 kg on the unprocessed diet.
Nutritional Intelligence at Play
The reanalysis suggests humans possess an inherent “nutritional intelligence,” guiding them toward balanced diets when presented with unprocessed options. “It’s exciting to see when people are offered unprocessed options, they intuitively select foods that balance enjoyment, nutrition, and a sense of fullness, while still reducing overall energy intake,” says Brunstrom. “Our dietary choices aren’t random — in fact, we seem to make much smarter decisions than previously assumed when foods are presented in their natural state.”
A 2025 clinical trial further supports these findings, showing that individuals on minimally processed diets lost twice as much weight as those on UPF diets, again due to reduced calorie consumption. Research continues to link UPFs to various health issues, though experts caution against overly restrictive policies, acknowledging that not all UPFs are equally detrimental.
What does this mean for your diet? Focusing on whole, unprocessed foods may allow you to eat satisfying portions while naturally reducing your calorie intake, tapping into your body’s innate ability to seek nutritional balance.
