Does Collagen Help With Weight Loss, or Cause Weight Gain?

Two small trials have tested collagen or gelatine for weight loss as the main outcome, with mixed results, and no weight-related claim for collagen is authorised in Great Britain.¹ What trials have measured is body composition: across 19 randomised trials in 768 adults, daily collagen peptides alongside resistance training added more fat-free mass than training alone, and the largest body-composition trials used 15 g a day.^{2, 5, 6, 7} Collagen does not cause weight gain either: it is protein, which food labelling counts at 4 kcal per gram, so 10 g is at most about 40 kcal.³ This page sits beneath the Wellgard collagen guide, beside the benefits of collagen powder.

Does collagen help you lose weight? What has and has not been tested

Two trials have had weight loss as the main outcome. In 72 adults on an eight-week weight-loss diet, gelatine in place of other protein gave the same fall in BMI as milk protein, set out below.¹¹ In a maker-run trial of 64 adults with overweight or obesity, two bars a day carrying 20 g of a bovine collagen treated to swell in the stomach cut body weight and BMI against a control group over 12 weeks.¹⁵ We found no trial with abdominal fat as its primary outcome. One body-fat trial without exercise exists: 90 overweight adults, 73 of them women, took 2 g a day of fish-skin collagen peptides or a placebo for twelve weeks, and body fat on DXA scan fell 1.2 kg in the collagen group while it rose 0.3 kg on placebo.⁴ It is one trial, with a manufacturer among its authors; the rest of the evidence comes from the training trials.

What did the body-composition trials measure?

Fat-free mass is everything that is not fat: muscle, bone, organs, connective tissue and water. The training trials measured it before and after twelve weeks of supervised resistance training, three sessions a week, with 15 g of collagen peptides or a placebo after each session. In 53 men aged about 72 with low muscle mass, fat-free mass rose 4.2 kg on collagen against 2.9 kg on placebo, and fat mass fell 5.4 kg against 3.5 kg.⁵ In 97 untrained middle-aged men, fat-free mass rose 3.42 kg against 1.83 kg and fat mass fell 5.28 kg against 3.39 kg; a third group on whey gained 2.27 kg and did not differ significantly from either.⁶ In 77 premenopausal women the same pattern held, with a larger gain in grip strength (collagen for women has the women's trials by outcome).⁷ Pooled across 19 trials, the effect size for fat-free mass was 0.48 with moderate certainty, and for maximal strength 0.19 with low certainty.²

Every one of those results came alongside training; that is the finding, not a limitation. Collagen adds to other protein rather than replacing it: in 22 older women, 30 g of whey twice a day for six days raised muscle protein synthesis over the six days and 30 g of collagen did not.⁸ Collagen lacks tryptophan, so it counts towards the day's protein, up to about a third of it, alongside the foods or whey that supply what it lacks.⁹ Collagen vs whey protein has the head-to-head trials.

Does collagen make you feel full?

Slightly, at one meal, in the one trial that measured it. In a 2025 UK crossover trial, 15 active women aged about 23 took 15 g of collagen peptides a day for a week; an hour after the final dose, following exercise, they ate about 41 kcal, roughly 10%, less at a free-choice meal than on a taste-matched control, with higher GLP-1 and insulin and no difference in how hungry they said they felt.¹⁰ But when gelatine, collagen before it is cut into peptides, replaced other proteins at a constant protein intake through an eight-week weight-loss diet in 72 adults, the fall in BMI was the same: 1.7 kg/m² against 2.1 and 1.6 on the milk-protein diets.¹¹ A fuller feeling after 15 g is a measurement; a weight result from it is not.

Does collagen cause weight gain?

Not on the evidence, and the arithmetic says why. Food labelling law counts protein at 4 kcal per gram, so 10 g of collagen is at most about 40 kcal and the 15 g the training trials used at most about 60 kcal; a tablet carries less collagen per unit and so fewer calories.³ Water retention is not a reported effect: the largest safety analysis, 35 trials in 3,165 people with osteoarthritis, found no more adverse events than control; the digestive effects that are reported are on is there a downside to taking collagen.¹² In the training trials the extra weight was fat-free mass, with fat mass falling at the same time.^{5, 6}

The one weight increase in the literature needs its context. When 37 overweight women ate an afternoon snack of either 38 g of hydrolysed collagen or 40 g of whey for eight weeks, matched for calories and protein, BMI rose 0.2 kg/m² on collagen and did not change on whey, and android fat, the abdominal region on a DXA scan, fell by 0.1 kg on whey.¹³ That compares two proteins at equal calories; it says nothing about collagen against no supplement, and 38 g is more than double the highest dose the training trials used.

Can collagen help loose skin after weight loss?

No trial has tested it. The closest, in 105 women aged 24 to 50 with moderate cellulite, gave 2.5 g a day for six months and reduced cellulite grade and thigh skin waviness in the normal-weight women, with a weaker effect in those who were overweight.¹⁴ Whether a peptide changes skin stretched for years is a gap in the evidence, not a result either way. What is known to help is a pace of loss the skin can follow, enough protein, resistance training and time; which collagen is best for sagging skin covers loose skin after weight loss.

Collagen on a GLP-1 weight-loss medicine: protein, muscle and skin

Appetite falls on a GLP-1 medicine and protein intake can fall with it; the trials that measured lean tissue during that weight loss are reported as counts on does Mounjaro cause muscle loss, and the protein target is on how much protein you need on Mounjaro. Collagen's place is as part of that protein total, not the whole of it: the muscle protein synthesis response came from whey, and collagen's gains came with training.^{2, 8}

No trial has tested collagen in people losing weight on a GLP-1 medicine. Should you take collagen on Mounjaro sets out the skin and hair evidence; Mounjaro face explains why facial volume loss is fat rather than collagen. Questions about the medicine itself belong with the prescriber or a pharmacist.

Is there a best time to take collagen for weight loss?

Not that a trial has shown. The training trials gave the 15 g straight after each session and daily on rest days; no trial has compared morning with evening, or before a meal with after it, on any outcome.^{2, 5} The trials support the same dose daily for eight to twelve weeks; when should I take collagen covers coffee, food, night and the levothyroxine gap.

Frequently asked questions

Why have I gained weight after taking collagen?

Not from the collagen's calories: 10 g is at most about 40 kcal of protein, and no trial reports weight gain attributable to collagen beyond the equal-calorie whey comparison above.^{3, 13} Look at what else changed when you started, including the sugars declared on the label of any flavoured format, and see a GP if a weight change is unexplained.

Does collagen reduce belly fat, and is there a best collagen for it?

No trial has tested collagen for abdominal fat as its main outcome, so there is nothing to rank. The one abdominal-fat measurement is the equal-calorie whey comparison, where android fat fell a little on whey and not on collagen; the training trials measured whole-body fat.^{5, 6, 13}

What is the best collagen for weight loss?

Two small weight-loss trials exist, with mixed results and different products, so nothing ranks one collagen above another for it. The body-composition trials used hydrolysed peptides at 15 g a day with training, so the label figure to read is grams of collagen per serving; how to choose a collagen supplement has the rest.²

Does collagen help with menopause weight gain?

No trial has tested it; the training trial in women recruited premenopausal women, and we found none of plain collagen with training in older women.⁷ Collagen and the menopause covers the trials after 50.

Can collagen replace a protein shake for weight management?

It adds to one. Collagen lacks tryptophan, and in the direct comparison whey raised muscle protein synthesis where collagen did not, so a complete protein does that job, with collagen counted as part of the total.^{8, 9} Collagen and creatine covers the other common pairing.

Sources

1. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register, 19 May 2026 edition. gov.uk.
2. Bischof K et al. Sports Med 2024. PubMed 39060741.
3. Regulation (EU) No 1169/2011 on the provision of food information to consumers, Annex XIV: conversion factors for the calculation of energy (assimilated GB law). legislation.gov.uk.
4. Tak YJ et al. Mar Drugs 2019. A manufacturer among the authors. PubMed 30866485.
5. Zdzieblik D et al. Collagen peptide supplementation in combination with resistance training improves body composition and increases muscle strength in elderly sarcopenic men: a randomised controlled trial. Br J Nutr 2015. PubMed 26353786.
6. Zdzieblik D et al. Int J Environ Res Public Health 2021. PubMed 33946565.
7. Jendricke P et al. Specific collagen peptides in combination with resistance training improve body composition and regional muscle strength in premenopausal women: a randomized controlled trial. Nutrients 2019. PubMed 31010031.
8. Oikawa SY et al. Whey protein but not collagen peptides stimulate acute and longer-term muscle protein synthesis with and without resistance exercise in healthy older women: a randomized controlled trial. Am J Clin Nutr 2020. PubMed 31919527.
9. Paul C, Leser S, Oesser S. Significant amounts of functional collagen peptides can be incorporated in the diet while maintaining indispensable amino acid balance. Nutrients 2019. PubMed 31096622.
10. Reynolds KM et al. The effects of collagen peptide supplementation on appetite and post-exercise energy intake in females: a randomised controlled trial. Br J Nutr 2025. PubMed 40685650.
11. Hochstenbach-Waelen A et al. Effects of a supra-sustained gelatin-milk protein diet compared with (supra-)sustained milk protein diets on body-weight loss. Br J Nutr 2011. PubMed 21272400.
12. Liang CW et al. Efficacy and safety of collagen derivatives for osteoarthritis: a trial sequential meta-analysis. Osteoarthritis Cartilage 2024. PubMed 38218227.
13. Giglio BM et al. Whey protein supplementation compared to collagen increases blood nesfatin concentrations and decreases android fat in overweight women: a randomized double-blind study. Nutrients 2019. PubMed 31480676.
14. Schunck M et al. Dietary supplementation with specific collagen peptides has a body mass index-dependent beneficial effect on cellulite morphology. J Med Food 2015. PubMed 26561784.
15. López-Yoldi M et al. Nutrients 2024. Maker-run: three authors employed by the collagen's maker. PubMed 39458544.