Biohacking Kompakt

Podcast episode 145 (in German)

Preserving muscle on weight-loss injections – what the scale does not tell you

November 22, 2026

A third of the kilos lost on weight-loss injections is muscle, it is often said. The episode shows what this figure actually measures, what users experience, and what training and new drugs change about the loss.

What it is about

The well-known figure comes from a substudy of STEP 1: just under 40 percent of the weight loss on semaglutide was fat-free mass. The X-ray method behind it, however, only sorts the body into fat, bone and everything else, and the rest also includes water, organs and the water-binding sugar store in muscle. Muscle is nevertheless lost too, on average 29 percent across 40 measurements on these injections, at the upper end of what weight loss costs anyway. In surveys, users report great satisfaction, but also concern about their muscles and fatigue; in 660 analyzed forum posts, many describe protein-rich meals and strength training. The conclusion: training is the best-supported muscle protection, and instead of looking only at the scale, it pays to look at stairs and chairs.

Key points

  • User report: in a British survey of 544 people who take or took the injection, almost one in two worried about their muscles, and over 60 percent felt so little energy that it held back exercise or everyday life.
  • Over 60 percent of the same respondents skipped meals at least 2 to 3 times a week, an obvious explanation for fatigue; fatigue is also mentioned by one in six of those with side effects in a little over 400,000 counted Reddit posts.
  • On MRI, the thigh muscles in a tirzepatide study in type 2 diabetes shrank only as much as the weight loss would predict, and the fat between the fibers declined more than expected.
  • According to a 2026 review, the share of fat-free mass in the loss falls to 7.7 percent with diet plus exercise, compared with a little over 22 percent without exercise; a second review gives 17.5 percent with strength training.
  • In the BELIEVE trial with 507 adults, fat-free mass fell over 48 weeks by up to 6.9 percent with semaglutide alone, and by at most 2.3 percent together with the antibody bimagrumab.
  • Enobosarm, known in the strength sports scene as ostarine, reduced the loss of fat-free mass after 16 weeks by 71 percent in 168 people aged 60 and over on semaglutide, according to the manufacturer’s press release.
  • On the stairs, a little over 4 in 10 participants under placebo lost considerable strength in this study, under enobosarm just under 2 in 10; as of September 2026 there was no peer-reviewed publication.

Where the data stop

Almost all figures on muscle loss come from the X-ray image, which does not separate muscle from water and organs. Whether the injection costs more than an ordinary diet has hardly been compared directly in studies; the two 2026 reviews disagree on this. The MRI study was analyzed retrospectively and paid for by the manufacturer, and the clinical study from Rouen with 4.5 kilos more grip strength after 1 year had no comparison group.

The muscle-protecting drugs are candidates with X-ray data. In BELIEVE, paid for by Eli Lilly, more than one in two in the combination groups had muscle cramps and around one in two acne, and grip strength was better than under placebo in only 1 of 4 combinations. In episode 138, bimagrumab built mass in older people without them walking better. Ostarine is on the doping list and not approved, there are case reports of liver damage, and products from the internet are not the study drug. Anyone who is older or has little muscle discusses weight loss with a doctor.

Listen (in German)

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Published on November 22, 2026.

The topic in the database

  • On weight-loss injections, fat-free mass is lost as well as fat, in STEP 1 just under 40 percent of the weight loss (DXA substudy, 140 participants)Preserving muscle on GLP-1

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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-09-25.