Researchers in the US have identified an antibody which could greatly reduce the loss of lean muscle mass in people who are taking weight-loss medications.

Lean body mass has been shown to account for up to 25 to 40 per cent of weight loss when taking GLP-1 medications, but taking apitegromab alongside the injections could halve the rate of muscle loss. Apitegromab is an antibody that selectively inhibits myostatin activation and is capable of increasing muscle mass.

The study involved 102 participants, half took apitegromab alongside their jabs and half took a placebo. After 24 weeks, total weight loss was almost identical across both groups, but the apitegromab group demonstrated 55 per cent greater retention of lean muscle mass when compared to the placebo group. Those on the placebo lost an average of 3.5kg of lean mass, while those on the muscle drug lost 1.6kg. 

This translates to a 30.2 per cent loss of muscle mass in the placebo group and a 14.6 per cent loss in the apitegromab group. 

Changes in body composition, including visceral fat, subcutaneous fat and trunk fat were similar between the two groups.

There was no measurable improvement in actual physical function or strength, such as grip strength, between the two groups.

Participants were assessed again eight weeks after the trial ended and the difference in lean mass between the apitegromab group and the placebo group remained significant. However, there were no notable differences in cardiometabolic parameters or physical function.

So the expertise and facilities of the fitness sector will still be essential even if apitegromab were to be rolled out widely.

This is unlikely to happen any time soon, as further research is needed to assess whether apitegromab could work on a wide-scale basis and whether or not people would be able to administer the jab themselves.

Published in Nature Medicine, the proof-of-concept study was called Apitegromab for lean mass preservation during tirzepatide-induced weight loss: a randomized, double-blind, placebo-controlled phase 2 trial and was a multi-centre trial which took place a number of specialised clinical research institutions.