Protein Intake: What the Evidence Actually Says About How Much You Need

The RDA of 0.8g/kg was built to prevent deficiency, not to optimize anything

The U.S. Recommended Dietary Allowance for protein — 0.8 grams per kilogram of bodyweight per day — is the amount research shows prevents nitrogen-balance deficiency in a sedentary adult. It was never designed or tested as an optimal target for muscle maintenance, healthy aging, or anyone doing resistance training. Treating the RDA as a ceiling, rather than the floor it was built to be, is the first myth worth clearing up.

The gym-folklore number ("1 gram per pound") isn't evidence-based either

The popular bodybuilding rule of roughly 1 gram of protein per pound of bodyweight (about 2.2g/kg) predates most of the controlled research on the question and overshoots what the actual trials support for most people. It isn't dangerous for a healthy adult, but it isn't specifically what the evidence points to — the real, research-backed range sits meaningfully lower.

What controlled research actually supports: roughly 1.2-1.6g/kg for most active adults, higher for aging muscle

Research on older adults with mobility limitations found that protein intake below the RDA worsens age-related declines in muscle size, quality, and function — but going above the RDA showed real, measurable benefit: intakes greater than 0.8g/kg attenuated lean-mass loss during calorie restriction and increased lean mass gains from resistance training.

A 2025 study in Frontiers in Nutrition tested this directly in elderly women with sarcopenia (age-related muscle loss), comparing the RDA (0.8g/kg) against a higher-protein diet (1.2g/kg). The higher-protein group showed significant improvements in muscle mass and strength that the RDA group did not. Combined with other 2025 clinical research, the emerging consensus for older adults — especially those with or at risk of sarcopenia — points to roughly 1.2 to 1.5g/kg, well above the traditional RDA.

• Sedentary healthy adults: the RDA of 0.8g/kg remains a reasonable floor, not necessarily an optimal target.
• Adults doing regular resistance training: research broadly supports higher intake, commonly cited in the 1.2-1.6g/kg range, to support muscle protein synthesis and recovery.
• Older adults, especially those with or at risk of sarcopenia: 2025 research supports going higher still, around 1.2-1.5g/kg, to counteract age-related muscle loss — a meaningfully different number than the RDA most people were taught.

The kidney-damage myth: debunked for healthy adults, a real caveat for existing kidney disease

A widely repeated warning — that high-protein diets damage the kidneys — traces back to a hypothesis first floated in the 1980s. Researchers at McMaster University examined more than two dozen studies and hundreds of participants in a meta-analysis published in the Journal of Nutrition and found no association between higher protein intake, even above 100g per day, and declining kidney function in healthy adults with normal blood pressure and blood sugar — including people at elevated risk from obesity, hypertension, or type 2 diabetes.

What actually happens is that kidneys temporarily increase their filtration rate (called hyperfiltration) to clear the additional metabolic byproducts of protein digestion. Research reviewed in the Journal of Nutrition and Metabolism found this is a normal, adaptive response in healthy kidneys — not evidence of damage.

A quick honest recap

• The RDA (0.8g/kg) is a floor built to prevent deficiency — not an optimal target for anyone who's active or aging.
• The "1 gram per pound" gym rule overshoots what controlled research actually supports for most people.
• Research broadly supports roughly 1.2-1.6g/kg for adults doing regular resistance training, and 1.2-1.5g/kg for older adults working to counteract age-related muscle loss.
• A McMaster meta-analysis of dozens of studies found no kidney-damage link from high protein intake in healthy adults, even above 100g/day — the kidneys' response (hyperfiltration) is normal and adaptive, not harmful.
• Existing kidney disease is a real, specific reason to get your protein target from a physician or renal dietitian instead of a general guideline.