Collagen protein bars show promise for safe and effective weight loss

Research being presented at this year's European Congress on Obesity (ECO 2025) and published in the journal Nutrients indicates that collagen could be a safe and effective weight-loss supplement.

Individuals with overweight and obesity who ate protein bars enriched with collagen, a protein that is found in connective tissue, lost twice as much weight as a control group who did not have the supplement. They also experienced greater decreases in blood pressure and waist circumference and saw their liver health improve more. They may also have increased skeletal muscle and fat-free mass. 

Many weight loss drugs are very expensive. We were interested in collagen because it is a protein that is cheap and easy to obtain and is not known to have any side-effects. It is also a compound that the public is familiar with.

Crucially, collagen's structure can be modified to allow it to absorb extra water, which leads to it growing in size.

We wanted to know if such a compound creates a feeling of fullness when it expands in the stomach, reducing appetite and leading to weight loss."

Dr. Paola Mogna-Peláez, researcher of the University of Navarra, Pamplona, Spain

To learn more, Dr Mogna-Peláez and colleagues conducted a 12-week randomised controlled trial involving 64 individuals aged 20-65 years with overweight or obesity (50% female, average weight 83.9 kg/13st 3lb, average BMI 29.65 kg/m²).

All of the participants were given healthy eating advice based on the Mediterranean diet. In addition, half of them were asked to a eat chocolate-flavoured protein bar enriched with collagen (10g of collagen per bar) with a glass of water before lunch and dinner each day. 

The collagen, which came from cows, had been treated to absorb extra water, so that it would increase in size when consumed with water.

The participants filled in an appetite questionnaire and underwent a range of body measurements and other tests and baseline and periodically thereafter.

At 12 weeks, the collagen group had lost more weight than the control group (3kg/6.6lb v 1.5kg/3.3lb). This was despite both groups consuming the same number of calories, say the researchers. 

Systolic blood pressure fell by 8 mm Hg in collagen group but rose slightly (0.4mm Hg increase) in the control group.

Waist circumference (2.8cm vs. 2.5cm), BMI (1.2 units vs. 0.78 units) and fatty liver index, a measure of liver health, also fell more in the collagen group than in the control group.

In addition, fat-free mass (non-fat tissue including muscle) increased in the collagen group, suggesting they may have built muscle, but remained unchanged in the control group.

The sarcopenic index, another measure of muscle mass increased in both groups.

Taken together, these results indicate that the weight loss in the collagen group was not due to loss of muscle, say the researchers, some of whom are employed by the firm that makes the supplement and the protein bars.

The questionnaire showed that the collagen group felt less hungry and more full than the control group. Levels of leptin, a hormone that induces feelings of satiety, fell in both groups but were higher at the end of study in the collagen group than in the control group.

In animal experiments, collagen decreased levels of ghrelin, a hormone that simulates appetite. The supplement also swelled to almost 20 times its original size in stomach acid and had low digestibility.

None of the participants reported any side-effects and those in the collagen group rated the bars very good (8.8 out of 10) for taste in a questionnaire – something the researchers say can likely be attributed to the bars being coated with sweetened dark chocolate. 

Dr Mogna-Peláez says: "Our results indicate that, by swelling in the stomach, the collagen made the participants feel less hungry, which would have led to them eating less and so losing weight.

"Collagen may also have led to the participants building muscle and we know that muscle burns more calories than fat.

"It is also possible that collagen changes the make-up of bacteria in the gut, which may aid with weight loss and appetite control."

The collagen-enriched protein bars are already on the market. The researchers are now running a larger trial to learn more about mechanisms of action, particularly in relation to the gut microbiota.