Collagen and weight: does it help you lose weight, or make you gain it?

2 questions arrive in our inbox about collagen and weight, from opposite directions: "will it help me lose weight?" and "will it make me fat?" The honest answer to both is mostly no. Collagen is a protein with about 4 calories a gram, no fat and no sugar. It isn't a weight-loss supplement, and it won't make you gain fat either. Here's the arithmetic, the 1 trial that's relevant, and where the marketing goes past the evidence.

The calories

Pure collagen peptides are about 90% protein and nothing else. Protein is 4 calories a gram, so:

• 2.5g a day (skin dose): about 10 calories
• 10g a day (joint dose): about 40 calories
• 15g a day (muscle dose): about 60 calories

For comparison, a teaspoon of sugar in your coffee is 16 calories and a slice of bread is around 80. At the doses the trials used, collagen is a rounding error in a day's eating. It can't make you fat on its own, and it can't make you lose weight on its own either. What matters is the total for the day.

The exception is flavoured collagen drinks and "beauty blends" with added sugar, creamers or oils. Those calories are real, and they're not from the collagen. Read the label: a pure powder has 1 ingredient.

Does collagen help you lose weight?

There is no trial showing collagen causes weight loss. What there is:

Body composition with training. In a 12-week trial, 53 older men did resistance training 3 times a week with either 15g of specific collagen peptides a day or placebo. The collagen group gained more lean mass, lost more fat mass (about 5kg vs 3.5kg) and got stronger. Everyone trained; the collagen improved the result of training. It didn't replace it, and nobody lost weight by taking collagen and sitting still.

Protein and fullness. Protein in general is more filling than carbohydrate or fat, calorie for calorie, and swapping a sugary snack for a protein one is a reasonable tactic. Collagen counts as protein for that purpose. But there's no good trial showing collagen specifically suppresses appetite better than any other protein, and at 2.5g to 10g a day it's a small amount; a boiled egg has 6g.

What we've dropped. Earlier versions of these pages said collagen "boosts metabolism", "regulates hunger hormones", "stabilises blood sugar" and "supports gut bacteria for weight management". None of that has human trial evidence behind it for collagen, so it's gone.

Does collagen make you gain weight?

Not fat, no. 2 things can move the scale though:

• Muscle, if you train. In the trial above the collagen group's lean mass went up. Muscle is denser than fat, so the scale can rise while you get leaner. That's the good kind of weight.
• Additives, if you buy the wrong product. Sweetened shots, flavoured powders and collagen "creamers" can carry 50 to 150 calories a serving from sugar and fat. Daily, that adds up.

If you started a pure collagen powder and gained fat, look at what else changed. The collagen is 40 calories; it's not the cause.

Where collagen fits if you're losing weight

Weight loss on a calorie deficit costs muscle as well as fat, and muscle is what keeps your metabolism and strength up. Protein intake and resistance training are the 2 things that protect it. Collagen can be part of your protein total, and the training trial suggests it helps the training work better, but it's not a complete protein: it's low in leucine, the amino acid that switches on muscle building. So:

• Hit your overall protein target with complete proteins (eggs, meat, fish, dairy, legumes, whey).
• Add collagen on top for skin, joints or tendon support, which are the things it actually has evidence for.
• If you take 15g with training, count the 60 calories. That's all.

Frequently asked questions

Does collagen break a fast?
Technically yes; it's protein and it triggers a small insulin response. If your fast is for calorie control, 10 calories is negligible. If it's for a medical or religious reason, treat it as food.

Is collagen keto or banting friendly?
Yes. Pure collagen has no carbohydrate. More in Collagen on a keto diet.

Can collagen cause bloating?
Occasionally, at higher doses or when started suddenly. Begin with half a dose for a week. It's uncommon with a pure powder; flavoured products with sugar alcohols are the usual culprit.

Which collagen for weight management?
None is a weight product. If you train, Active at 15g. Otherwise pick by your real goal: Which collagen should I use?

The studies

• Zdzieblik D et al. (2015). Collagen peptide supplementation in combination with resistance training improves body composition and increases muscle strength in elderly sarcopenic men. British Journal of Nutrition 114:1237–1245. Read it free →

This article is general information, not medical advice. If you're managing your weight for a medical reason, work with your doctor or a registered dietitian.

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