Lean Body Mass · Watcher v1.14.2

The 290 ± 25 kJ / kg fat / day figure (Alpert, 2005) defines the theoretical upper bound on adipose lipolysis. The rate-limiting step is hormone-sensitive lipase (HSL), the primary enzyme for intracellular triglyceride hydrolysis in adipocytes.

This ceiling only applies in a fully fasted state. Any caloric intake elevates insulin, which suppresses HSL via the cAMP–PKA signalling axis: insulin activates phosphodiesterase 3B, lowering cAMP and leaving HSL dephosphorylated and inactive. In a normal eating pattern, postprandial insulin suppression restricts effective fat mobilisation for most waking hours, pushing the realistic daily ceiling well below 69 kcal / kg fat.

Targeting 100% therefore creates a structural deficit that fat stores cannot fully cover. The gap is filled through gluconeogenesis (catabolism of skeletal muscle protein), which drives disproportionate LBM loss. Settings below 60% keep the deficit within what adipose tissue can realistically sustain under normal dietary conditions.

Muscle protein synthesis caps how fast lean mass accrues — the surplus that turns into muscle is small because muscle tissue is ~75% water and energetically cheap. This slider scales the target surplus from 0 to that MPS ceiling. Any intake beyond it is stored as fat, not muscle, so a higher number does not build muscle faster.

Your target body-fat %. Weight and LBM are projected forward daily under the Alpert deficit until this threshold is reached. The resulting date and weight become the cut endpoint shown on both charts.

Height is used for BMI and FFMI. FFMI 25 marks the natural upper bound (Kouri et al., 1995). Activity level scales BMR to full TDEE.

Total daily calories including all activity. Enter a value manually, or press Calculate TDEE to run Katch-McArdle against today's smoothed LBM. More accurate than weight-only estimates when body composition is tracked.

Everything stays in your browser's localStorage. No server, no account, no cloud. Export a backup before erasing; there's no undo.

Plain UTF-8 CSV, three columns. Dates are ISO 8601. BF% is optional per row and exports as an empty field when absent. The last #params row stores all settings and is restored on import.

date: YYYY-MM-DD (ISO 8601)
weight: kilograms
bodyfat: percent, optional per row
#params: settings snapshot

Health disclaimer
This app is for informational use only and does not constitute medical advice. Consult a qualified healthcare professional before making significant changes to your diet or training. Calculations are based on peer-reviewed research (Alpert, 2005; Kouri et al., 1995) but individual physiology varies. Do not rely solely on this app to make health decisions.

Privacy
All data lives exclusively on your device in browser localStorage. Nothing is collected, transmitted, or stored on any server. No analytics, no advertising, no account. The only external connection is the optional Buy Me a Coffee page, which opens only when you tap the link at the bottom of the screen.

Full privacy policy →

Fill in several days at once. Each row is one measurement. Press + to add a row; the date steps forward by one day automatically. Weight is required, BF% is optional. Rows with no weight are skipped. Existing entries for the same date get overwritten.

Editing overwrites this measurement. Changing the date moves the entry; if another entry already exists on the new date, it is replaced.