Creatine and GLP-1s: do they protect muscle mass?

GLP-1 drugs have become the most talked about weight loss tool of the moment, but they have also raised a recurring question: how much muscle do you lose on them, and how can you protect it? In this conversation, two specialists review the evidence on resistance training and creatine in people using GLP-1s, and explain why much of the panic about muscle loss stems from a flawed measurement.

Why DEXA misleads

DEXA splits the body into three compartments: bone, fat and everything else. That third bin gets labelled lean mass, even though it includes water, glycogen, organ tissue and the fat stored inside muscle and liver. When you lose weight, all of it drops at once.

GLP-1s are especially good at reducing ectopic fat, the fat stored where it should not be: in the liver, inside muscle and around the organs. The problem is that DEXA cannot tell those changes apart from real muscle and adds them up as lean mass loss. That is why the numbers look scarier than they should.

How much muscle do you really lose?

The historical benchmark says about a quarter of all the weight lost is lean mass, a figure similar to a diet without exercise. But that lean mass is not only contractile tissue; it is also water, glycogen and ectopic fat. Functional muscle loss tends to be smaller than the DEXA reading suggests.

What the evidence says about resistance training

Studies on GLP-1s and resistance training are still small, but they point in the same direction:

• In the SLIGHT trial, with liraglutide, those who did resistance training lost about half as much lean mass and also got stronger.
• The T-REX study, with preliminary results, shows that the resistance training arm roughly halved lean mass loss compared with the GLP-1 alone.

This is the same relationship seen when comparing diet alone with diet plus exercise. The practical takeaway is clear: adding strength work to a GLP-1 preserves muscle.

An optimistic hypothesis

One of the specialists offers a bolder idea: GLP-1s, with or without training, may preserve real contractile tissue better than diet alone, precisely because they remove so much ectopic fat. Newer glucagon agonists such as retatrutide or survodutide clear liver fat so dramatically that a large share of the lean mass loss actually comes from the liver, not muscle. His colleague prefers caution until more data arrive.

The measurement problem

Both agree on a central point: we need better tools. MRI lets you see liver and intramuscular fat directly, something DEXA cannot do. If manufacturers used MRI in their studies, they could show how much contractile tissue is truly preserved. They also look ahead to combinations, such as amylin agonists (for example cagrilintide) or myostatin inhibitors, that could improve results further.

What about creatine?

Creatine has never been studied specifically in GLP-1 users. Outside that context its effect is modest: it slightly improves strength performance thanks to more intracellular energy, letting you do a few more reps or lift a little more. On hypertrophy the effect is small and works mainly through greater training load.

There is a pre-registered pilot trial at the University of Saskatchewan: 40 people starting a GLP-1 receive 10 grams of creatine a day or placebo while following a three day per week strength programme for twelve weeks. The hypothesis is that creatine will improve lean tissue maintenance, but with such a small sample and both groups training, detecting a difference will be hard.

Practical tips

• If you use a GLP-1, prioritise resistance training two or three times a week.
• Look after your protein intake to support muscle adaptation.
• Do not fixate on a single DEXA scan and read the results in context.
• Creatine can be added if you are interested, but do not expect miracles for muscle mass.
• Adjust your rate of weight loss so you do not shed tissue too fast.

Conclusion

The fear of losing muscle on GLP-1s is largely inflated by a measurement tool that confuses ectopic fat with muscle. Resistance training is the best supported intervention to preserve contractile tissue, creatine offers a small and as yet untested benefit in this group, and MRI will be key to answering the question definitively.