A new study has found that collagen-enriched protein bars could be a safe, low-cost way to help people lose weight and improve their health.
Researchers shared their findings at the 2025 European Congress on Obesity and published the full study in the journal Nutrients. The study suggests that people who ate these special protein bars lost twice as much weight as those who didn’t.
What Is Collagen and Why Does It Matter?
Collagen is a protein found naturally in the body, especially in skin and connective tissues. In this study, researchers used collagen from cows and treated it so it could soak up water and expand. When eaten with water, the collagen-filled bars grew in size in the stomach, helping people feel fuller, faster.
“We wanted to see if this fullness could help reduce hunger and support weight loss,” said Dr. Paola Mogna-Peláez from the University of Navarra in Spain, who led the study.
How the Study Worked
The study included 64 adults between the ages of 20 and 65 who were either overweight or obese. Half of the participants were given chocolate-flavored protein bars containing 10 grams of collagen. They ate one before lunch and one before dinner, always with a glass of water. Everyone in the study received advice on healthy eating based on the Mediterranean diet.
After 12 weeks, the group eating collagen bars had lost an average of 3 kilograms (about 6.6 pounds), while the other group had lost just 1.5 kilograms (about 3.3 pounds). Both groups ate the same number of calories overall, showing that the difference was likely due to the collagen bars.
More Than Just Weight Loss
The collagen group also showed other health improvements:
- Lower blood pressure: Their systolic blood pressure dropped by 8 mm Hg, while it slightly increased in the control group.
- Smaller waists: Their waist size dropped slightly more than the other group (2.8 cm vs 2.5 cm).
- Better liver health: Their fatty liver index improved more than the group without collagen.
- More muscle: Their fat-free mass (which includes muscle) increased, while it stayed the same in the other group.
The researchers said this suggests that the participants lost fat without losing muscle — and may have even built some muscle.
Why Did It Work?
Participants who ate the collagen bars reported feeling less hungry and more satisfied. Hormone levels supported these feelings. The group had higher levels of leptin, a hormone that helps control hunger, and in earlier animal studies, collagen was shown to lower ghrelin, a hormone that makes people feel hungry.
In lab tests, the collagen expanded to nearly 20 times its size when exposed to stomach acid, making people feel full without eating more food.
No Side Effects, Good Taste
No one in the collagen group reported any side effects. In fact, they rated the bars very highly in terms of taste — 8.8 out of 10 — likely because of the sweet dark chocolate coating.
What’s Next?
Collagen-enriched protein bars are already available on the market. The team is now doing a larger study to learn more about how the bars work, especially how they might change the bacteria in the gut — which could also play a role in weight and appetite.
Dr. Mogna-Peláez said the results are exciting: “Collagen seems to help reduce hunger, support fat loss, and possibly even boost muscle. That makes it a promising and safe option for people looking to lose weight.”
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