The Recommended Dietary Allowance for protein has sat at 0.8 grams per kilogram of body weight per day for decades. It was set to prevent nitrogen loss in the average sedentary adult, not to build or preserve muscle.
A growing body of exercise and geriatric research now indicates that most people who lift weights, and most people over 65, need considerably more than that.
For adults training for muscle growth, the most-cited benchmark comes from a 2018 systematic review and meta-analysis in the British Journal of Sports Medicine that pooled 49 trials and 1,863 participants. The analysis found that additional protein continued to enhance gains from resistance training up to roughly 1.62 grams per kilogram per day, after which the extra intake stopped adding measurable fat-free mass.
The confidence interval around that estimate extends to about 2.2 g/kg/day, which is why the practical range of 1.6 to 2.2 g/kg/day has become the standard recommendation for lifters.
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That is roughly two to nearly three times the current RDA of 0.8 g/kg/day, which the National Academies set based on nitrogen balance in healthy adults, not on muscle-building outcomes.
Older adults need more, not less
The gap between the RDA and current evidence is arguably widest for older adults.
Aging blunts the muscle-building response to a given dose of protein, a phenomenon researchers call anabolic resistance.
In a 2013 position paper, the international PROT-AGE Study Group recommended that healthy adults over 65 aim for 1.0 to 1.2 g/kg/day, with 1.2 g/kg/day or higher for those who exercise, and 1.2 to 1.5 g/kg/day for older adults with acute or chronic illness.
The group flagged one important exception. Older people with severe kidney disease and an estimated GFR under 30 mL/min/1.73 m2, who are not on dialysis, may need to restrict rather than increase protein and should follow their physician's guidance.
Distribution across the day matters
Total daily grams are not the whole story. Muscle protein synthesis, the process the body uses to repair and add muscle tissue, is triggered by a threshold dose of protein at each meal rather than by a running total.
A 2018 review in the Journal of the International Society of Sports Nutrition by Brad Schoenfeld and Alan Aragon recommends consuming protein "at a target intake of 0.4 g/kg/meal across a minimum of four meals" to reach 1.6 g/kg/day, and up to 0.55 g/kg per meal to reach the 2.2 g/kg upper end. For most adults, that works out to roughly 25 to 40 grams of high-quality protein per sitting.
The overnight window
The stretch between dinner and breakfast is the longest fasting period most people go through, and it coincides with a natural dip in muscle protein synthesis.
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Work led by Jorn Trommelen and Luc van Loon at Maastricht University suggests that a dose of protein before sleep can partly close that gap.
Their 2016 review in Nutrients concluded that "at least 40 g of dietary protein should be ingested prior to sleep to elicit a robust stimulation of muscle protein synthesis rates throughout the night," with the largest benefit when combined with an evening resistance-training session.
Anyone with kidney disease, diabetes, or other chronic conditions should talk to their doctor before making large changes to protein intake, since individual targets can differ from the population averages above.
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