Why 0.8 g/kg is a floor, not a target
The official RDA for protein is 0.8 grams per kilogram of body weight per day. That number is widely misread. It was set as the minimum that prevents deficiency in nearly all sedentary adults — the amount below which you start losing body protein. It says nothing about what is optimal for someone who trains, diets, or is over 60.
For a sedentary 70 kg adult, 56 g a day genuinely is enough to stay healthy. Add lifting, running, a calorie deficit, or age, and the useful intake climbs well past it. That is why this calculator offers four targets instead of one.
What the evidence says for building muscle
The best single reference is a 2018 meta-analysis by Morton and colleagues in the British Journal of Sports Medicine: 49 trials, 1,863 participants. Extra protein stopped improving muscle gain at around 1.6 g/kg per day, with the confidence interval reaching about 2.2. That gives the working range you see repeated across sports nutrition — 1.6 to 2.2 g/kg — and this calculator's build-muscle setting of 1.8 sits in the middle of it.
Dieting changes the math. In a calorie deficit the body is readier to burn amino acids for fuel, so protein needs rise exactly when eating gets harder. Intakes around 2.2 g/kg help keep the weight you lose coming from fat rather than muscle, which is why the cutting option is the highest of the four. Pair it with a sensible deficit from the calorie deficit calculator, and let the macro calculator fill in carbs and fat around it.
Spreading it across the day
Total daily grams matter most. Distribution is the tiebreaker: muscle protein synthesis responds meal by meal, and each sitting maxes out its effect at roughly 0.3–0.4 g/kg — about 25–35 g for most people. Four meals of 35 g build slightly more muscle than one 140 g feast, even though the total matches.
Hence the per-meal split in the results above. A practical day at 140 g looks ordinary: eggs and yogurt in the morning, chicken and rice at lunch, a normal dinner, and something before bed. The food table exists because "140 grams" is abstract until you see it as four and a half chicken breasts or 23 eggs.
Plant and animal protein
Animal proteins contain all nine essential amino acids in the proportions muscle wants; most single plant sources run short on one — grains on lysine, legumes on methionine. Combining sources across the day fixes the profile without any careful pairing at each meal, and soy, tofu, and quinoa are complete on their own. If you eat fully plant-based and train hard, aim toward the top of your range and let bulk come from lentils, tofu, seitan, and a pea or soy powder when convenient. The difference is real but small, and total grams still decide most of the outcome.
