The body scanner

The body scanner tracks body composition with the camera on the phone you already own. Each scan is dated and sits on the same timeline as your weight, food and doses. That is the only way to tell recomposition, losing fat while holding or gaining muscle, from the scale simply going down.

How it works, step by step

1. Scan with the phone camera. No extra hardware.
2. The scan is dated. It goes on the timeline beside weight from Apple Health or Health Connect, the food log and the dose log.
3. Repeat it. One scan is a snapshot. A series, taken under similar conditions, is a trend.

Why weight alone misleads

Weight is fat, lean tissue, water and everything else added together. When it falls, you cannot tell from the number which of those fell. On a GLP-1 receptor agonist this matters. In the STEP 1 trial of semaglutide 2.4 mg, the body composition substudy found that lean mass made up roughly 40 percent of the weight lost. Fat fell by more, so the body ended up proportionally leaner, but some of what came off was not fat. The lean mass studies page goes through the trials.

The opposite case is just as common. Someone who starts lifting while eating more protein can lose fat and gain muscle at the same time, and the scale barely moves. Judged on weight alone, it looks like nothing is working. Body mass index has the same blind spot: it is calculated from height and weight only.

Can a phone camera measure body composition?

The reference methods, such as DXA, are accurate but need a clinic and cost money each time. Consumer alternatives have generally been less accurate. Camera-based estimation is newer, and the best published validation comes from one specific system.

Two cautions. That study tested one particular algorithm; it shows the approach can work, not that every camera method performs the same way, including the one in this app. And any method is most useful for change in the same person over time, measured the same way each time. Consistent conditions, such as similar clothing, lighting and time of day, make repeated scans more comparable.

Scale, tape and scan: what each tells you

None of these is complete on its own. Weight and a dated composition scan on the same timeline, with food, training and doses beside them, is the combination that answers the question most people actually have.

Who it is for

• People on a GLP-1 receptor agonist who want to know whether they are keeping muscle as weight comes off. See the muscle loss page.
• Anyone training in a deficit who suspects the scale is understating their progress.
• People running a protocol aimed at body composition who want a measure more specific than weight.

How it connects to the rest of the app

Scans share the timeline with the dose log, nutrition, training, weight from the wearable integrations and bloodwork. Put together, they answer the question weight cannot: what changed. Remi can answer questions using your scans alongside the rest of your log. Body scan data is removed along with everything else if you delete your account, as described on the privacy and data page.

Take a first scan before the next dose step or training block, then one every few weeks under the same conditions. The line will tell you more than the scale. The app is on the download page.