The RDA for protein is dangerously low for anyone over 40

After 40, the muscle protein synthesis response to dietary protein is blunted — a phenomenon called anabolic resistance. Multiple isotope tracer studies show that adults over 60 require 1.2–1.6g of protein per kilogram of bodyweight per day just to prevent negative protein balance — 50%+ more than the 0.8g/kg RDA. Gabrielle Lyon synthesizes this research into a practical target: 1g of protein per pound of ideal bodyweight (2.2g/kg) for active adults, with at least 30–50g per meal to overcome the leucine threshold for protein synthesis signaling.

Skeletal muscle is the largest site of glucose disposal, the primary producer of myokines (including irisin and IL-6 post-exercise), and the major determinant of resting metabolic rate. Sarcopenia — age-related muscle loss — drives insulin resistance, increases fall and fracture risk, and is independently associated with all-cause mortality. Every decade after 30, untreated adults lose 3–8% of muscle mass. This is not inevitable — it is a protein and resistance training deficit.

The key amino acid for muscle protein synthesis is leucine — it directly activates mTORC1, the master regulator of muscle protein synthesis. A minimum of 2–3g of leucine per meal is required to trigger the anabolic response. Animal proteins (meat, eggs, dairy) typically provide this threshold at 30–50g portions. Plant proteins require larger portions or combining to achieve equivalent leucine delivery. The timing around resistance training (within 2 hours) amplifies the synthesis signal 2–3× above fasted conditions.

Stokes et al. (Nutrients, 2018) reviewed dietary protein for muscle hypertrophy with resistance training: spreading sufficient high-quality protein across 3–4 meals per day — each meeting the per-meal leucine threshold — maximises the muscle protein synthesis response and underpins preservation of lean mass with age.

A meta-analysis of 49 randomised controlled trials in 1,863 healthy adults doing at least six weeks of resistance training found that protein supplementation added a small but real amount on top of the training itself: 0.30 kg of fat-free mass and 2.49 kg on one-rep-max strength. A breakpoint analysis placed the point of diminishing returns at a total protein intake of about 1.62 g/kg/day — past that, extra supplemental protein produced no further gains in fat-free mass. That estimate is imprecise, though: its 95% confidence interval ran from 1.03 to 2.20 g/kg/day, and the authors suggested ~2.2 g/kg/day as the prudent target for anyone wanting to maximise gains. The fat-free-mass benefit of supplementing shrank with increasing age and was larger in people already resistance-trained. This looked at supplements added on top of habitual eating, so it describes where extra protein stops helping rather than a universal requirement.

A systematic review of 43 randomised trials, 30 of them pooled, compared plant with animal protein for muscle outcomes. Plant protein was associated with slightly lower muscle mass after the intervention than animal protein (standardised mean difference -0.20, 95% CI -0.37 to -0.03), with the gap seen in adults under 60 and not statistically detectable in those 60 and over, and showing up only in trials that paired protein with resistance training. Soy versus milk protein showed no pooled difference; the gap came from non-soy plant proteins — rice, chia, oat and potato — and from whole plant-based diets. Overall muscle strength and physical performance showed no difference, though animal protein did edge out plant protein for lower-body strength in the over-60s specifically. The authors describe the effect as small, note substantial variation between trials, and say a wider range of plant proteins still needs testing.

Blake, Galpin and colleagues (J Int Soc Sports Nutr, 2025) randomised 17 well-trained adults — roughly 8 to 9 per group — to either a 16:8 time-restricted eating window or normal all-day feeding, while training four times a week for 8 weeks on a 10% calorie surplus with protein at 2.2 g/kg/day. Both groups gained strength, muscular endurance and fat-free mass. The time-restricted group completed less total training volume and gained 4.0 ± 1.9 kg less on squat 1RM (p = 0.05, borderline), and reported lower daily energy at week 4. Fat-free mass gains numerically favoured the time-restricted group (2.67 against 1.82 kg), while all-day feeding added 1.4 ± 0.6 kg more fat. The authors conclude 16:8 is viable during a building phase when calories and protein are adequate. With 17 people in total, this applies to well-trained young adults on a supervised surplus and should not be stretched further.