The RDA is a floor, and it was never meant to be a target
The number almost everyone quotes — 0.8 g of protein per kg of body weight — is the Recommended Dietary Allowance. Read the definition carefully: it is the amount that meets the requirement of 97.5% of healthy adults, established from nitrogen balance studies designed to answer one question — how little protein can you eat without going into deficit? That is a floor for avoiding harm, not an amount that optimises muscle, satiety, bone density or recovery.
Nearly everything measured since has pointed the same direction. When the outcome is lean mass retention in a deficit, strength gains with training, or appetite control, more protein than 0.8 g/kg performs better — up to a plateau. The calculator above uses the bands from that literature rather than the deficiency floor.
The evidence bands
| Situation | g / kg / day | 75 kg person |
|---|---|---|
| RDA — sedentary floor | 0.8–1.0 | 60–75 g |
| Generally active | 1.2–1.6 | 90–120 g |
| Building muscle | 1.6–2.2 | 120–165 g |
| Endurance training | 1.2–1.7 | 90–128 g |
| Older adults (65+) | 1.2–1.5 | 90–113 g |
| Lean and cutting | 2.3–3.1 of FFM | 138–186 g at 20% fat |
The last row is the one people get wrong. The International Society of Sports Nutrition sets 2.3–3.1 g/kg for lean, resistance-trained people in a calorie deficit — but per kg of fat-free mass, not scale weight. Body fat does not need feeding, so applying a per-kg figure to total weight inflates the target for anyone carrying appreciable fat. That is why the calculator asks for body fat percentage on that setting; if you don't know it, estimate with the body fat calculator.
Per meal: about 0.4 g/kg, three to five times
Muscle protein synthesis responds to a dose, and the response saturates. The practical rule from the dose-response work is roughly 0.4 g/kg of body weight per meal — around 30 g for a 75 kg person — repeated across three to five meals. Eating 150 g of protein in two sittings is not wasted, but spreading it produces more total stimulus across the day.
Why leucine is the trigger
Of the twenty amino acids, leucine is the one that flips the switch: it activates the mTOR pathway that initiates muscle protein synthesis. A meal needs roughly 2.5–3 g of leucine to hit the threshold reliably, which is what about 30 g of a high-quality protein delivers. This is also the mechanistic reason distribution matters at all — below the threshold, a meal feeds you without signalling growth.
Plant versus animal protein
Animal proteins — dairy, eggs, meat, fish — are more digestible and richer in leucine, so gram for gram they trigger a larger synthesis response. Plant proteins tend to be lower in one or more essential amino acids (grains in lysine, legumes in methionine) and are less completely absorbed. None of this makes plant-based diets inadequate; it means the target moves up and the sourcing gets more deliberate:
- Aim for the top of your band rather than the middle.
- Lean on soy, seitan and pea protein, which are closest to animal protein for muscle purposes.
- Combine across the day — legumes with grains covers the gaps without any need to pair them in a single meal.
The safety question, answered plainly
“High protein wrecks your kidneys” is the most persistent myth in nutrition, and it comes from a real fact applied backwards. People with established chronic kidney disease are often advised to restrict protein to slow progression. That is true, and it says nothing about healthy kidneys. Trials in healthy, trained adults at intakes up to about 3 g/kg — some running a year or longer — find no deterioration in kidney function, bone density or liver markers.
Two genuine caveats remain. If you already have reduced kidney function, your protein intake is a clinical decision — check where you stand with the GFR calculator and talk to your doctor. And a very high protein intake displaces other food: at 3 g/kg there is simply less room for carbohydrate to train on, which is a performance cost rather than a health one.
Fitting protein into the rest of the diet
Protein is the macro you set first because it is anchored to your body rather than your calorie total. Once it is fixed, calories decide the direction — use the TDEE calculator — and carbohydrate and fat divide what remains. The macro calculator does that division and shows the whole plate at once.
One last practical note: protein has the highest thermic effect of the three macros, with roughly 20–30% of its calories spent on digestion and processing. It also has the strongest effect on satiety per calorie. Neither of those makes protein magic, but together they explain why people in a deficit consistently report an easier time at 2 g/kg than at 1 g/kg, at identical calories.