Can protein bars act as weight loss supplements? Important facts to know

Protein bars are absolutely adored by fitness enthusiasts. They come in all sizes, shapes, and flavours. Many opt for protein bars as a quick breakfast or snack option. The protein content promised on the label is the major reason for its popularity amongst fitness enthusiasts. But what if a protein bar could help you lose weight? According to a new Spanish study, protein bars have shown potential as a weight-loss aid.

New research being presented at this year’s European Congress on Obesity (ECO 2025) and published in the journal Nutrients suggests that protein bars containing collagen could be a safe and effective weight-loss supplement. Collagen, a protein commonly found in connective tissue. The researchers found that individuals with overweight and obesity, who ate protein bars enriched with collagen, lost twice as much weight compared to those who didn’t consume them. The participants also showed a reduction in blood pressure, waist circumference, and improvement in liver function. 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,” researcher Dr Paola Mogna-Peláez, of the University of Navarra, Pamplona, Spain, said in a statement.

The researchers conducted a 12-week randomized controlled trial in 64 adults aged 20 to 65, with an average body mass index (BMI) of 29.65. All participants were advised to follow a Mediterranean-style diet. Half the group was additionally asked to consume a chocolate-flavored protein bar containing 10 grams of collagen with water before lunch and dinner. The collagen, which came from cows, had been treated to absorb extra water, so that it would increase in size when consumed with water.

At the end of the study, the protein bar group lost an average of 3 kilograms (6.6 pounds), compared to 1.5 kilograms (3.3 pounds) in the control group, despite both groups consuming the same number of calories.


The collagen group felt less hungry and fuller than the control group. Levels of leptin, a hormone that induces feelings of satiety, fell in both groups but were higher in the collagen group than in the control group. No side effects were reported.

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

“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,” Dr Mogna-Peláez said.

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