How much protein do you really need, and from which sources?

Where 0.8 comes from. The official recommended allowance was set as the smallest amount that prevents a loss of body nitrogen, not as the best amount. The accepted range for protein is 10% to 35% of calories, and even the bottom of that range sits above the allowance¹.

Older adults. An expert group recommends at least 1.0 to 1.2 g/kg a day for people over 65, at least 1.2 g/kg if they exercise, and 1.2 to 1.5 g/kg for those with acute or chronic illness². Among 2,066 adults aged 70 to 79, those in the top fifth for protein lost about 40% less lean mass over 3 years than those in the bottom fifth⁹.

Lifters. In 49 trials of resistance training, protein supplements added a little muscle and strength. Gains leveled off at about 1.6 g/kg of total daily protein, with the upper end of the estimate at 2.2 g/kg³.

Spreading it out. Eating about 30 g at each of three meals raised 24-hour muscle protein synthesis by 25% compared with a day that put 63 g at dinner⁵. Older men needed about 0.40 g/kg in one meal to get the maximum response, versus 0.24 g/kg for young men⁶. For a 70 kg older adult, that is about 28 g.

Which protein. Pooling 31 cohorts, plant protein went with lower all-cause and cardiovascular mortality, and an extra 3% of calories from plant protein with 5% lower death risk⁷. In two big US cohorts, replacing 3% of calories from processed red meat with plant protein was linked to 34% lower mortality⁸.

What it looks like. Per 100 g cooked, lentils and black beans give about 9 g of protein, a hard-boiled egg 12.6 g, salmon 22 to 25 g and ground beef 26 g. A cup of cooked lentils (198 g) provides about 18 g¹⁰.

Safety. In 28 trials, higher-protein diets did not reduce kidney filtration in healthy adults⁴. Higher intakes also showed no harm to bone and a small gain at the lumbar spine¹¹.

Related reading: sarcopenia, whey protein, pea protein and beans and legumes.

Muscle and strength. Morton and colleagues pooled 49 trials (1,863 participants) of resistance training lasting at least six weeks. Protein supplementation increased one-repetition-maximum strength by 2.49 kg (95% CI 0.64 to 4.33), fat-free mass by 0.30 kg (0.09 to 0.52) and muscle fiber area by 310 square micrometers. The benefit shrank with age and was larger in trained people. A break-point analysis put the plateau at 1.62 g/kg a day (95% CI 1.03 to 2.20). Authors reported ties to the US National Dairy Council and a sports-supplement maker³.

Older adults. The PROT-AGE group's recommendations are a consensus statement, not a trial; it notes evidence on quality and timing is insufficient for firm advice². The Health ABC cohort tracked 2,066 adults aged 70 to 79 with DXA scans: the top quintile of protein lost 0.50 kg of lean mass versus 0.88 kg in the bottom quintile, a pattern that held after adjusting for fat mass change but is observational⁹. Moore and colleagues re-analyzed lab studies of healthy men (about 71 and 22 years old): muscle protein synthesis plateaued at 0.40 g/kg per meal in older men versus 0.24 in younger (p = 0.055), and these were single-meal measures, not long-term outcomes⁶. Mamerow's crossover trial in 8 adults compared 7 days of even protein (about 30 g per meal) with a skewed pattern (11, 16 and 63 g); even eating gave 25% higher 24-hour muscle protein synthesis. It was tiny, short, measured synthesis rather than muscle size, and the authors reported ties to beef-industry groups⁵.

Source and mortality. Naghshi's meta-analysis of 31 cohorts (715,128 people, 113,039 deaths) found total protein was linked to lower all-cause mortality (pooled effect 0.94), plant protein to lower all-cause (0.92) and cardiovascular mortality (0.88), and animal protein was not clearly related to cardiovascular or cancer mortality⁷. In the Nurses' Health Study and Health Professionals Follow-up Study (131,342 people), animal protein was associated with higher cardiovascular mortality (hazard ratio 1.08 per 10% of energy) and plant protein with lower all-cause mortality (0.90 per 3% of energy), mostly in people with at least one unhealthy lifestyle factor; substituting plant protein for processed red meat gave 0.66⁸.

Conflicting evidence. Levine and colleagues found that adults aged 50 to 65 reporting high protein intake had 75% higher mortality and a fourfold higher cancer death risk over 18 years, attenuated if the protein was plant-derived, whereas in those over 65 high intake went with lower mortality. Mouse experiments supported a growth-factor mechanism. The senior author holds equity in a company that develops medical foods¹². These results oppose Naghshi's pooled finding and illustrate how much the answer depends on age and source.

Kidneys and bones. Devries and colleagues pooled 28 trials (1,358 healthy adults) comparing high protein (at least 1.5 g/kg or 20% of energy) with lower protein. Post-intervention filtration rate was trivially higher with more protein (standardized difference 0.19), and its change did not differ (0.11, 95% CI -0.05 to 0.27). Risk of selection bias was unclear and the data do not cover people with kidney disease⁴. A review of 16 trials and 20 cohorts found moderate evidence for a small lumbar-spine bone density gain (0.52%) with more protein and no effect at hip or whole body, with no adverse effects¹¹.

Bottom line (confidence 3 of 5). The floor is 0.8 g/kg. For lifters and older adults, 1.0 to 1.6 g/kg is better supported than the floor, and in healthy people higher intakes appear safe for kidneys and bones. Plant-leaning sources look best in cohorts, but the evidence is observational.