A caloric deficit means consuming fewer calories than your Total Daily Energy Expenditure (TDEE). Since your body needs that energy from somewhere, it draws on stored body fat (and to a lesser extent, muscle) to make up the difference, which is the fundamental mechanism behind all fat loss.
Higher protein intake and continued resistance training both help direct weight loss in a deficit toward fat rather than muscle. Use our TDEE calculator to find your maintenance number, then apply a deficit from there.
Scaling rate of loss to bodyweight, not a flat calorie number
A flat “300 to 500 calorie deficit” ignores that the same deficit is a much bigger disruption for a 130 lb person than a 250 lb person. A more accurate way to set a target rate of loss is as a percentage of bodyweight per week:
- 0.5 to 1% of bodyweight per week is a sustainable range for most people, translating to roughly a 500 to 750 calorie daily deficit for someone around 180 lb, and proportionally smaller for lighter individuals.
- Leaner individuals (already close to a healthy or athletic body-fat range) should target the lower end of that range, since they have less fat mass to draw on and a larger deficit disproportionately risks lean mass and performance.
- Higher body-fat individuals can tolerate a somewhat larger deficit, closer to 1%, without the same lean-mass or performance cost, because more of the energy gap is realistically covered by fat stores.
Percentage-of-bodyweight targets also self-correct as you lose weight: the deficit in absolute calories naturally shrinks as your bodyweight (and TDEE) drops, which is one reason weight loss often needs a periodic recalculation rather than one fixed number held for months.
Protecting lean mass in a deficit
Three levers matter most for keeping a deficit fat-focused rather than muscle-focused:
- Protein intake. Aim for the higher end of typical ranges (around 1.8 to 2.4g per kg of bodyweight, see macros) since protein needs rise, not fall, in a deficit to counteract elevated muscle protein breakdown.
- Resistance training. Continuing to train with adequate training volume and intensity signals to your body that the muscle is still needed, which is the single strongest defense against losing it during weight loss.
- Deficit size. Larger deficits increase the proportion of weight lost as lean mass, independent of protein and training; this is a direct reason to prefer the smaller end of the 0.5 to 1% bodyweight range when preserving muscle matters.
Metabolic adaptation
As you lose weight, TDEE drops for two separate reasons: a smaller body simply burns fewer calories at rest and during activity (mechanical adaptation), and the body also becomes modestly more energy-efficient beyond what smaller body size alone predicts (adaptive thermogenesis). This second effect means a deficit that worked at the start of a diet often stops producing loss after several weeks, even with unchanged intake, and it’s the main reason progress should be judged by a rolling weight trend rather than any single week, with the target recalculated periodically rather than held fixed for the entire diet.