Macro split for fat loss vs muscle gain

Start with calories, not macros

Total Daily Energy Expenditure (TDEE) = Basal Metabolic Rate × activity multiplier. Mifflin-St Jeor gives BMR within ±10% for most non-extreme body compositions, and the activity multiplier ranges from 1.2 (sedentary) to 1.9 (heavy manual labor or twice-daily training). Our calorie calculator does this in one step.

Fat loss target: TDEE minus 15–25%. A 2,800-calorie TDEE becomes a 2,100–2,400 calorie target, producing roughly 1–1.5 lb/week of weight loss. Going more aggressive than 25% is usually counterproductive — muscle loss accelerates, training quality collapses, and adherence breaks.

Lean bulk target: TDEE plus 10–15%. The same 2,800-calorie TDEE becomes a 3,100–3,200 calorie target. Slower than that and you're not stimulating much new muscle; faster and you accumulate fat without proportionally more lean mass. The honest version is that a true natural lean bulk gains roughly 1–2 lb/month, not the 1 lb/week the bro-science sites promise.

Maintenance: TDEE within ±5%. Useful between bulk and cut phases, after a long deficit, and for performance athletes whose body composition is already where it needs to be.

Protein is the macro that earns its keep

Protein has the highest thermic effect of food (20–30% of its calories are burned during digestion), the highest satiety per calorie, and is the only macro that directly supports muscle protein synthesis. Skimp on it during a deficit and you lose muscle alongside fat; skimp on it during a surplus and you gain disproportionate fat.

Targets, expressed per pound of body weight: 0.8–1.0 g/lb for general health and maintenance, 1.0–1.2 g/lb during a calorie surplus, and 1.0–1.3 g/lb during a calorie deficit (yes, the deficit target is HIGHER — you need more protein to preserve lean mass when calories are low). Round to the nearest 5g; precision below that is noise.

A 180 lb person aiming for fat loss would target 180–230g of protein daily. At 4 calories per gram, that's 720–920 calories from protein, which fits comfortably inside a 2,100–2,400 calorie deficit budget. Source matters less than total — animal protein, dairy, soy, and well-combined plant proteins all support muscle protein synthesis with broadly similar leucine adequacy.

Fat is a floor, not a residual

Dietary fat supports hormone production (testosterone and estrogen both require cholesterol substrate), fat-soluble vitamin absorption, and cellular membrane integrity. Set fat as a minimum floor, not as 'whatever's left after protein and carbs.' Falling below the floor for extended periods correlates with reduced sex hormone production and joint discomfort.

Minimum fat: 0.3 g/lb body weight for short-term cuts, 0.4 g/lb for sustained periods. A 180 lb person targets 55–75g/day. Above that, fat is interchangeable with carbs by personal preference and training style.

Carbs fill the remaining calorie budget. Total calories minus protein calories minus fat calories, divided by 4 (since carbs are 4 cal/g), equals your carbohydrate target. For most athletes, carbs end up being the largest single macro, particularly in a maintenance or surplus phase.

Putting it together: a worked cut, maintenance, and bulk

180 lb intermediate lifter, sedentary office job, four lifting sessions per week, TDEE = 2,500 calories. Cut at 20% deficit = 2,000 calories. Protein 1.2 g/lb = 216g (864 cal). Fat 0.35 g/lb = 63g (567 cal). Carbs = (2,000 − 864 − 567) ÷ 4 = 142g. Expect 1–1.5 lb/week scale loss for 8–12 weeks, then diet break.

Same lifter at maintenance: 2,500 calories. Protein 1.0 g/lb = 180g (720 cal). Fat 0.4 g/lb = 72g (648 cal). Carbs = (2,500 − 720 − 648) ÷ 4 = 283g. Body composition holds; training output rebounds after a deficit phase.

Same lifter on a lean bulk at 12% surplus: 2,800 calories. Protein 1.0 g/lb = 180g (720 cal). Fat 0.4 g/lb = 72g (648 cal). Carbs = (2,800 − 720 − 648) ÷ 4 = 358g. Expect roughly 1 lb/month scale gain, of which 40–70% will be lean tissue depending on training experience and recovery quality. Truncate the bulk when you've added 8–15 lb or when waist circumference creeps above your comfort range, then cut.

Track the trend, not the day-to-day. A weekly average weight is signal; a single morning weigh-in is noise. Photos at the start of each phase capture what the scale can't.