BMI stands for Body Mass Index — a simple numerical measure of body weight relative to height. It is calculated by dividing your weight in kilograms by your height in metres squared (kg/m²). The result places you in one of four general categories: underweight, healthy weight, overweight, or obese.
Why BMI is controversial
On its own, BMI cannot distinguish between fat mass and muscle mass, account for age, sex, or ethnicity, or tell you where fat is stored. That makes it an incomplete picture of health — which is exactly why AlterMe does not rely on it alone.
AlterMe does not use BMI as a measure of your health. It uses it as one input in a safety calculation — and only for that purpose.
What BMI tells the algorithm
At a higher BMI, your body has more stored energy available and can sustain a larger daily deficit without triggering the metabolic adaptations that stall progress — muscle loss, slowed metabolism, hormonal shifts. AlterMe allows for a more aggressive deficit here because the physiology supports it.
At a lower BMI (healthy weight range), your body protects lean muscle mass more aggressively. A deficit that is too large starts pulling from muscle, not fat — which slows your metabolism and makes results harder to maintain. AlterMe moderates your deficit at this range to protect your body composition.
How it works in the calculation
Your final daily deficit is a blend: 70% your chosen pace, 30% a physiological adjustment based on your current BMI. The two work together so your plan stays ambitious where your body can handle it and conservative where it needs to be.
How it changes over time
As you lose weight your BMI drops, and the adjustment shifts with it. Your deficit rate naturally moderates as you get closer to a healthy weight — not because the plan is getting easier, but because your body needs a different approach at that stage. It is a built-in safeguard, not a slowdown.