About a quarter of the weight lost is lean tissue, and the two things that change that are protein and resistance training. This page covers both, and what Loopa scores.
The number
In the SURMOUNT-1 body-composition substudy, roughly 75% of the weight lost was fat mass and roughly 25% lean mass, similarly for tirzepatide and for placebo (Look M et al., Diabetes, Obesity and Metabolism, 2025 · doi:10.1111/dom.16275).
Losing some lean tissue while losing weight is ordinary. It is not a side effect of a medicine and it is not unique to anybody on one.
Lever one: protein
Covered in full on Protein first on a GLP-1. The short version: 1.6 to 2.4 g/kg/day is the range recommended for people training in an energy deficit (Hector AJ and Phillips SM, IJSNEM, 2018 · PMID 29182451), and gains in fat-free mass plateau around 1.6 g/kg/day (Morton RW et al., BJSM, 2018 · doi:10.1136/bjsports-2017-097608).
Lever two: resistance training
The American College of Sports Medicine's position stand on physical activity for weight loss and prevention of regain is the general reference here (Medicine & Science in Sports & Exercise, 2009 · doi:10.1249/MSS.0b013e3181949333), and its companion stand covers how training progresses over time (MSSE, 2009 · doi:10.1249/MSS.0b013e3181915670).
Resistance training also loads bone. High-intensity resistance and impact training improved bone mineral density in postmenopausal women with low bone mass (Watson SL et al., Journal of Bone and Mineral Research, 2018 · doi:10.1002/jbmr.3284), and the NIH's own patient guidance describes resistance exercise as putting stress on bone that can make it stronger (NIAMS).
Two or three sessions a week that you actually do beats a program you abandon.
Lever three, quietly: sleep
One night of sleep deprivation reduced muscle protein synthesis in a controlled study (Saner NJ et al., Physiological Reports, 2021 · doi:10.14814/phy2.14660). It is not a lever anybody markets, and it is real.
The lean-mass protection score
Loopa can score how well the things within your control are lining up. It is out of a fixed weight and it says what it counted.
- Protein against your goal
- Resistance training frequency
- Sleep
- Body composition, where you have measurements or DEXA results on file
It needs 14 days of both food and training data before it scores at all, and it says so rather than producing a number from three days. Where there is no weight on file to compute a protein goal from, the score is empty rather than zero: a missing input is not a bad result.
The body-composition part redistributes across the others until you have two body-fat points, from any source Loopa accepts. Every input names the source behind it.
The copy says "your own training results" and never "counteract". The score describes what you did. It does not claim anything about your medication.
How Loopa helps
- See the score: Health › Protocols › Lean mass.
- Log training: Health › Workouts, set by set. Logging is free.
- Short sessions for low days: Health › Protocols › This week offers micro-workouts when your own check-ins say energy is low.
- Record body composition: Health › Measurements, and DEXA results go in as lab markers.
Related
Where this comes from
Everything on this page is drawn from peer-reviewed research and published position stands, cited above. The full list is at loopahealth.app/sources. Loopa does not give medical advice and never sets or changes a dose.
