--- title: App That Tells You If You’re Losing Fat or Muscle | ProgressLens url: https://progresslens.app/fat-or-muscle-loss-app/ language: en updated: 2026-11-13 --- # The app that tells you if you’re losing fat or muscle By the [ProgressLens team](https://progresslens.app/about/) · Updated November 13, 2026 The scale says you lost 10 pounds. It doesn’t say what they were made of. Short answer ProgressLens tells you whether you’re losing fat or muscle. Its AI Progress Report includes a muscle-loss signal: it compares how fast your waist is shrinking with your arms and shoulders, checks your weekly rate of weight loss, and reads your matched photos. If your limbs shrink as fast as your waist while weight drops quickly, it flags it and tells you what to do. **On this page** - [How the muscle-loss signal works](#how) - [Built for GLP-1 journeys](#glp1) - [What to measure](#measure) - [FAQ](#faq) ## How the muscle-loss signal works When you lose mostly fat, your waist shrinks much faster than your arms and shoulders. When you lose muscle too, your arms and shoulders shrink almost as fast. ProgressLens tracks both over 4 to 8 weeks, adds your weekly weight change, and shows one of these states: | State | What it means | | On track | Your waist is shrinking faster than your arms and shoulders: mostly fat loss. | | Watch | Your arms and shoulders are shrinking too. Keep lifting and keep protein high. | | Possibly losing muscle | Limbs shrinking as fast as the waist while weight drops quickly. Slow down, prioritise strength training and protein. | | Not enough data yet | Log weight, waist and arms or shoulders a few weeks apart to turn it on. | **Your progress report** Where you are 16–18% Estimated body fat · medium confidence - From photos: 15–19% - From tape measurements: 17.2% What changed Weight **−3.1 lb**Waist **−0.8 in** - Waist: more defined - Abs: more defined - Shoulders: unchanged Is it working On track Your waist is shrinking faster than your arms and shoulders: mostly fat loss. What to do next Cut - Lose 0.7–1.1 lb a week - About 12 weeks to around 12% body fat - Next check-in in about two weeks, in the same place and light. Estimates from your photos and measurements, not a medical assessment. Sample report. Illustrative numbers. ## Built for GLP-1 journeys On semaglutide (Ozempic, Wegovy) or tirzepatide (Mounjaro, Zepbound), weight can drop fast, and clinical substudies with DXA scans found that roughly 25–40% of the weight lost was lean mass. Tell ProgressLens you’re on a GLP-1 in the About you step and the report puts the fat vs muscle check first and reminds you to talk to your clinician about protein and strength training. It doesn’t track doses and isn’t medical advice. ## Get your own Progress Report. Take a check-in, tap AI Analyze and get your Progress Report: body-fat range, what changed, fat or muscle, and whether to cut or bulk. On iPhone, iPad and Android, with no account. Your photos stay on your phone. ## What to measure - Weekly: weight, waist, front and side photos. - Every 1–2 weeks: arms (relaxed, at the widest point) and shoulders. - Monthly: chest and thighs. No app yet? Run the free [fat vs muscle loss calculator](https://progresslens.app/tools/fat-vs-muscle-loss-calculator/) with two body-fat readings. FAQ ## Frequently asked questions **How can I tell if I’m losing fat or muscle?** Compare your waist with your arms and shoulders over a few weeks. If your waist drops much faster, it’s mostly fat. ProgressLens does this automatically and adds what it sees in your photos. **Can it tell if I’m losing muscle on Ozempic, Wegovy or Mounjaro?** It gives you a muscle-loss signal. If your arms and shoulders shrink as fast as your waist while your weight drops quickly, the report flags it and suggests what to do. It’s an early warning from your photos and tape measurements, not a medical test, so talk to your clinician too. **Can a smart scale tell me if I’m losing muscle?** Bioimpedance scales estimate it, but readings swing with hydration, which changes a lot on a GLP-1. Tape measurements plus matched photos are a steadier signal for trends. **What should I do if it says I may be losing muscle?** Slow the rate of loss, strength-train at least twice a week, eat enough protein, and talk to your clinician if you’re on medication. **Are my photos private?** Yes. They stay inside the app on your phone, not in your gallery or a cloud, and there’s no account. When you tap AI Analyze, only the photos you chose for that report are sent to the AI. They’re not stored and not used to train any AI. ## Keep reading [AI progress photo analysisWhat AI Analyze reads and what the report tells you.Read more →](https://progresslens.app/ai-progress-photo-analysis/)[Sample Progress ReportEvery section of a real-format report, explained.Read more →](https://progresslens.app/sample-progress-report/)[AI body fat: photo + tapeWhy two sources beat one photo.Read more →](https://progresslens.app/ai-body-fat-from-photo-and-tape-measure/)[Bulk or cut appA clear verdict from your own photos.Read more →](https://progresslens.app/bulk-or-cut-app/) --- ProgressLens is an AI progress photo app for iPhone, iPad and Android that turns your check-in photos and tape measurements into a Progress Report: your body-fat range, what changed, whether you are losing fat or muscle, and whether to cut, lean bulk, recomp or maintain. App Store: https://apps.apple.com/app/progresslens/id6806300575 Google Play: https://play.google.com/store/apps/details?id=app.progresslens