These Spaniards have studied a cheap and effective protein for weight loss (and without side effects).

Collagen , a structural protein found in connective tissue, has been the subject of numerous studies. Some studies show that supplementation with its hydrolyzed form promotes changes in the skin, such as a reduction in wrinkle formation or increased elasticity and hydration.

Now, new Spanish research published in the journal Nutrients indicates that collagen could be a safe and effective weight-loss supplement . Specifically, they studied overweight and obese people who consumed collagen-enriched protein bars . The results show that this group lost twice as much weight as those who did not take the supplement . And that's not all: the analysis claims they also experienced greater decreases in blood pressure and waist circumference, and improved liver health.

However, "not all collagens are created equal." "The collagen in this study is very special because it undergoes a process that increases the protein network's ability to store water between the fibrils . That's why it swells, and it also swells in the acidic pH of the stomach, thus increasing satiety," Fermín Milagro , one of the lead authors, explains to this newspaper.

Milagro works as a researcher at the Nutrition Research Center of the University of Navarra , in the Department of Food Sciences and Physiology, at the Navarra Health Research Institute (IdiSNA) and at the Biomedical Research Network Center for the Pathophysiology of Obesity and Nutrition , also known as CIBERobn.

"Only this type of technologically treated collagen has this effect; other non-hydrolyzed types can't do that. And the other type sold, which is hydrolyzed, doesn't have this capacity either because it no longer has fibrils , only shorter collagen peptides. The latter are used primarily for joint and sports issues because they are absorbed faster, although the final effect on these two parameters isn't much greater than with longer, non-hydrolyzed collagens," he continues.

Researchers conducted a 12-week randomized controlled trial involving 64 overweight or obese individuals aged 20 to 65. All participants received healthy eating advice and were asked to consume a protein bar enriched with 10 grams of collagen with a glass of water before each meal.

" Many weight-loss medications are very expensive. We were interested in collagen because it's a cheap and easy-to-obtain protein, and there are no known side effects. It's also a compound that's familiar to the general public ," adds Paola Mogna-Peláez , another of the authors who belongs to the same research group.

That collagen, which they explain came from cows , had been treated to absorb additional water, so that it would increase in size when consumed with that glass of water. "It's essential that the structure of collagen can be modified to allow it to absorb more water, which causes it to grow in size. We wanted to know if this compound creates a feeling of satiety by expanding in the stomach, reducing appetite and causing weight loss," the expert continues.

From that point on, the participants completed an appetite questionnaire and underwent a series of body measurements and other tests, both at baseline and periodically. At the end of the weeks, the collagen group had lost 3 kilos and the non-collagen group had lost 1.5 kilos, despite the same calorie intake. Systolic blood pressure decreased by 8 mmHg in the collagen group, but increased slightly (0.4 mmHg) in the collagen group.

Additionally, waist circumference (2.8 cm vs. 2.5 cm), BMI (1.2 units vs. 0.78 units), and fatty liver index also decreased more in the collagen group. Another aspect highlighted in the study is the increase in fat-free mass after taking the supplement. However, the sarcopenic index , another measure of muscle mass, increased in both groups.

The questionnaire showed that the collagen group felt less hungry and more full . Although levels of leptin, the hormone that induces feelings of satiety, decreased in both groups, they were higher in those taking the supplement at the end of the study.

"It undergoes a process that increases the protein network 's ability to store water between the fibrils. That's why it swells, and it does so in the acidic pH of the stomach , thus increasing satiety and reducing the desire to eat . It's taken a little before main meals so that, when the meal arrives, a smaller amount is ingested without feeling hungry," explains researcher Milagro.

"Collagen is a protein that gives rise to textures and flavors that aren't very appealing, which is why they are often flavored."

Thus, the results, presented at the 2025 European Congress on Obesity , indicate that the weight loss in the collagen group "was not due to a loss of muscle mass." Regarding side effects, participants reported none .

Finally, when asked about the not-so-healthy ingredients some bars of this type contain, such as maltitol or lecithin, the lead author states that "all" have some sweeteners or emulsifiers "to improve their organoleptic characteristics ." "Collagen is a protein that gives rise to textures and flavors that aren't very appealing, which is why they are usually flavored and enhanced. The best thing for your health would be to choose those with the fewest additives of this type," he concludes.