How much protein per kg of body weight depends on what the number is for: the RDA of 0.8 g/kg is the adult minimum for the general population,1 while people who train are usually set somewhere between 1.2 and 2.4 g/kg. Zyra Nutrition turns that range into four tiers, adds a bump on a deficit, and caps the result so it cannot crowd out the other macros.
This article gives the numbers, where each one comes from, and a worked example you can reproduce on the protein calculator.
The RDA versus the training range
The Recommended Dietary Allowance is the intake that covers the needs of nearly all healthy adults — it is a floor, not an optimum for anyone with a training goal. The Institute of Medicine sets it at 0.8 g/kg of body weight per day (56 g/day for the reference adult man, 46 g/day for the reference adult woman), inside an acceptable range of 10–35% of energy.1
The training literature works higher. A large meta-analysis on the question pooled 49 randomised trials (1,863 participants) of resistance training lasting at least six weeks and found that adding protein increased gains in strength and fat-free mass, but that intakes above roughly 1.6 g/kg/day did not add further fat-free mass.2 Practical targets in sports-nutrition guidance run above that figure as a margin for individual variation and for dieting, not because the pooled data showed more gain there; Zyra Nutrition's own tiers above the plateau (2.0, 2.4 g/kg) are that margin, written into the formula.
In plain terms: 0.8 is enough to not be short; around 1.6 is where the measured muscle benefit levelled off in trained people; the range above it is a margin for error and for dieting.
How much the extra protein added
The effect was real but small next to training itself. Across the 49 trials, training alone added about 1.1 kg of fat-free mass on average; adding protein raised that gain by 0.30 kg (95% CI 0.09 to 0.52) and the gain in one-rep-max strength by 2.49 kg, about 9%.2 The authors put it plainly: training was "a far more potent stimulus" than the added protein.2 These are group averages over about 13 weeks, not a result any one person can expect.
Fat-free mass means everything that is not fat: muscle, water, organs and bone, measured here by a DXA body scan. A 95% confidence interval (CI) is the range the true average most likely sits in.
The extra protein did not help everyone equally. Resistance-trained people gained more from it than beginners, and people older than 45 gained less, though the older groups were mostly given small doses (about 20 g a day).2
Extra lean-mass gain when protein was added to training, by group · kg
The 1.6 g/kg figure itself is less exact than it looks. It came from 42 study groups (723 people) with intakes from 0.9 to 2.4 g/kg/day. The break point was 1.62 g/kg/day, but its 95% CI ran from 1.03 to 2.20, and the two-line model was not statistically significant (p = 0.079).2 That is why the authors wrote that "it may be prudent to recommend ~2.2 g protein/kg/d" for people trying to maximise gains.2
Later meta-analyses asked the dose question in a different way. One pooled 105 trial reports (5,402 people) and modelled the gain per extra 0.1 g/kg/day: about 0.39 kg of lean mass below a total of 1.3 g/kg/day, and about 0.12 kg above it, over several months.3 So the curve flattens rather than stopping dead.
Lean-mass change per extra 0.1 g/kg a day of protein · kg
A 2022 meta-analysis of 74 trials found the lean-mass effect with resistance training was statistically significant in adults under 65 eating 1.6 g/kg/day or more, and in adults 65 and over at 1.2–1.59 g/kg/day.4 It called the extra gains "small".4
In plain terms: more protein helps a little, most clearly up to somewhere between about 1.3 and 1.6 g/kg; past that, returns shrink, and the training does most of the work.
The four tiers we use (table)
Zyra Nutrition does not ask you to pick a number. It asks for a preference and maps it to a tier:
| Tier | g/kg (maintain or gain) | g/kg (losing goal) | 60 kg | 80 kg | 100 kg |
|---|---|---|---|---|---|
| Low | 1.2 | 1.4 | 72 / 84 g | 96 / 112 g | 120 / 140 g |
| Moderate | 1.6 | 1.8 | 96 / 108 g | 128 / 144 g | 160 / 180 g |
| High | 2.0 | 2.2 | 120 / 132 g | 160 / 176 g | 200 / 220 g |
| Extra high | 2.4 | 2.6 | 144 / 156 g | 192 / 208 g | 240 / 260 g |
The tiers are the constant PROTEIN_G_PER_KG = {1.2, 1.6, 2.0, 2.4} in the algorithm; each cell is body weight × tier, rounded to the gram. The low tier sits at the bottom of the active range, moderate at the meta-analysis breakpoint, and the top two above it.
Why more on a deficit
When the goal is set to lose, the algorithm adds 0.2 g/kg to the selected tier before it calculates grams. The reasoning is arithmetic as much as physiology: on a deficit the calorie total falls, so the same grams of protein become a larger share of a smaller budget, and the food that carries protein becomes the part of the diet the algorithm protects first. Fat has a floor and carbohydrate takes the cut — protein is the one number that goes up.
A moderate-tier 80 kg person at maintenance is set 128 g. The same person on a losing goal is set 80 × 1.8 = 144 g.
When protein gets capped
Two guardrails sit on top of the tiers.
The 50% cap. Protein calories may not exceed half of the calorie target. If grams × 4 comes to more than 0.5 × target, protein is reduced to target × 0.5 ÷ 4 grams and the calculator says so. This mostly triggers when a heavy person picks the extra-high tier on an aggressive deficit.
The 3.0 g/kg warning. If the tier plus the deficit bump ever exceeds 3.0 g/kg, the algorithm raises a warning. With the current tiers the highest reachable value is 2.6 g/kg, so the warning is a safety net for future tiers, not something a user sees today.
Worked example
A 100 kg person on a losing goal, extra-high tier, whose calorie target has come out at 1,800 kcal:
| Step | Arithmetic | Result |
|---|---|---|
| Tier + deficit bump | 2.4 + 0.2 | 2.6 g/kg |
| Raw protein | 100 × 2.6 | 260 g = 1,040 kcal |
| 50% cap | 1,800 × 0.5 | 900 kcal allowed |
| Capped protein | 900 ÷ 4 | 225 g |
The result on the protein calculator is 225 g with a "protein capped at 50% of calories" note. The same person on the moderate tier would be set 180 g (720 kcal, 40% of the target) with no cap.
In plain terms: the tier picks the grams, the deficit adds a little, and the cap stops protein from taking over a small calorie budget.
What the studies found
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Morton et al., *Br J Sports Med*2 | 49 randomised trials, 1,863 healthy adults, resistance training for 6 to 52 weeks, not dieting | Added protein raised the fat-free-mass gain by 0.30 kg on average; gains levelled off at 1.62 g/kg/day (95% CI 1.03–2.20) | 2018 |
| Tagawa et al., *Nutr Rev*3 | 105 randomised-trial reports, 5,402 people | Each extra 0.1 g/kg/day went with about 0.39 kg more lean mass below 1.3 g/kg/day and 0.12 kg above it | 2020 |
| Nunes et al., *J Cachexia Sarcopenia Muscle*4 | 74 randomised trials in healthy, non-obese adults | Small extra lean-mass gains with resistance training; significant under 65 at ≥1.6 g/kg/day, at 65 and over at 1.2–1.59 g/kg/day | 2022 |
| Kanaan, Nait-Yahia & Doucet, *Eur J Clin Nutr*5 | 21 college-aged athletes, 6 weeks at a 25% calorie deficit with lifting | Groups at about 1.2, 1.6 and 2.2 g/kg all lost fat and gained fat-free mass; protein intake made no difference | 2025 |
Limits worth knowing
- Weeks, not years. The trials in the 2018 meta-analysis ran 6 to 52 weeks, about 13 on average.2
- Nobody was dieting. That meta-analysis included only people at or above their energy needs, so it says little directly about a deficit.2
- Few older adults and women. Only 13 of the 49 studies were in people over 45, and the authors note far less work in women.2
- The break point is loose. Its range spans
1.03to2.20 g/kg/dayand the model was not statistically significant.2 - Funding. One author declared grant support from a national dairy council that also funded some of the reviewed trials.2
- Abstracts only for the 2020, 2022 and 2025 papers; the claims here stay inside what those abstracts report.
Latest research
The newest trial we read is a 2025 study in 21 college-aged athletes who trained three days a week on a 25% calorie deficit for six weeks.5 They were randomly assigned about 1.2, 1.6 or 2.2 g/kg of protein a day. All three groups lost fat mass and gained fat-free mass, with no difference by protein intake, and the authors concluded that 1.2–1.7 g/kg "appear sufficient" for most athletes during a deficit.5 It is small and short, so it cannot rule out a benefit of higher intakes; it is one reason the +0.2 g/kg deficit bump is a margin, not a measured requirement.
The short version
0.8 g/kg is the adult RDA — the population minimum.1 Zyra Nutrition's tiers are 1.2 / 1.6 / 2.0 / 2.4 g/kg, plus 0.2 on a deficit; the moderate tier matches the point where a large meta-analysis found fat-free-mass gains stopped rising.2 Protein is capped at 50% of calories and flagged above 3.0 g/kg. Every figure is grams of total body weight, and the protein calculator reproduces each row of the tables above.
- In trials, extra protein added a small amount of lean mass on top of training; the training did most of the work.2
- The benefit flattened somewhere between about
1.3and1.6 g/kg/day, with wide uncertainty up to about2.2.32 - Trained lifters gained more from extra protein than beginners.2
Educational overview only — not medical advice. Zyra is a training and nutrition tracking tool; the numbers here are the algorithm's rules and published reference values, not an individual prescription.
