Active adults need 1.6 g/kg/day of protein. Older adults, anyone in a deficit, and anyone on a GLP-1 should push to 2.0 to 2.2 g/kg. The Morton 2018 meta-analysis (n=1,863 across 49 RCTs) is the canonical reference for the 1.6 g/kg muscle-protein-synthesis plateau in resistance-trained adults. Phillips 2016 makes the case that older adults need slightly more, around 1.8 to 2.0, to overcome anabolic resistance. The mTOR-longevity argument against high protein has preclinical support but weaker human outcome data, and applies to a narrower audience than its proponents typically suggest.
The audience question is the one that actually settles the debate. The protein-restriction case rests on rodent caloric restriction studies and human observational data dominated by populations who under-eat protein at baseline. If you are healthy, active, and past 40, the sarcopenia risk of under-consuming protein is larger than the mTOR-chronic-activation risk of over-consuming. Sarcopenia kills more elderly than cancer and is a bigger predictor of late-life functional decline than almost anything else in the lab panel.
The mechanism is straightforward. Skeletal muscle is the largest insulin-sensitive tissue, the largest amino-acid reservoir, and the primary buffer against falls and frailty. Each kilogram of lean mass lost after 40 raises the next decade's mortality risk meaningfully. The dose-response for resistance training plus adequate protein is one of the best-documented in the longevity literature.
Practical thresholds: 1.6 g/kg/day if you are healthy, active, under 60, and at maintenance calories. 2.0 g/kg if you are over 60, in a caloric deficit, on a GLP-1, training hard for hypertrophy, or recovering from injury or illness. 2.2 g/kg if multiple of the above conditions stack, especially older plus deficit. Above 2.5 g/kg, additional intake yields no measurable lean-mass benefit in the trial literature, though it is not harmful in healthy kidneys.
Distribution matters less than total. Splitting protein across 3 to 4 meals at 30 to 50 g each is convenient but offers small benefit over 2 larger feedings if total daily protein is matched. Don't over-optimize meal timing at the cost of total intake.
- Active adult target: 1.6 g/kg/day. For a 75 kg person, ~120 g/day.
- Older or cutting target: 2.0 to 2.2 g/kg/day. Same 75 kg person: 150 to 165 g/day.
- Quality: complete sources (animal protein, soy, dairy) make this trivial; plant-only requires more total grams plus deliberate combining.
- Diminishing returns: above 2.5 g/kg, no measurable lean-mass benefit in healthy adults.
- Where the mTOR critique applies: chronic disease populations, advanced cancer, possibly very low activity at all ages. Not the typical reader.
What to actually do
- Calculate your number once. Body weight in kg times 1.6 (active under 60), 2.0 (over 60 or cutting), or 2.2 (cutting plus older or on a GLP-1).
- Anchor it to a meal architecture. 30 to 50 g protein at breakfast, lunch, and dinner closes most of the gap. Add a fourth feeding (snack or shake) if your number is >150 g/day.
- Track for 14 days, then stop tracking. Most people undershoot their protein target by 20 to 40 g/day until they measure. Two weeks of weighing gets the eye calibrated. After that, you don't need to track unless something drifts.
The protein conversation has more noise than signal because two camps argue past each other, with different audiences in mind. Most readers of this site are in the audience that wins from more, not less. For the full breakdown of the meta-analyses, the mTOR critique, and the older-adult case, see the full article.