A 2022 meta-analysis in the British Journal of Sports Medicine synthesizing 49 randomised controlled trials found that protein supplementation beyond 1.62 g per kilogram of body weight per day produced no additional gains in muscle mass or strength — yet global nutrition surveys consistently show that adults over 50 consume on average only 1.0 g/kg/day, leaving a significant gap between intake and the threshold needed to prevent age-related muscle loss (sarcopenia). Understanding your personal protein target is one of the highest-return nutritional decisions you can make, regardless of whether your goal is athletic performance, healthy aging, or weight management.
This guide breaks down the physiology of protein metabolism, current evidence-based intake recommendations, source quality, and distribution strategy. Related: Iron Deficiency Anemia: Dietary Management
Protein Basics and Physiology
Dietary protein is hydrolysed in the stomach and small intestine into individual amino acids and small peptides, which are absorbed via specific intestinal transporters and enter the portal circulation. The liver extracts a portion for gluconeogenesis and urea synthesis; the remainder enters systemic circulation to supply all tissues.
Proteins perform thousands of functions in the human body: structural (collagen, actin, myosin), enzymatic (all biochemical reactions), hormonal (insulin, growth hormone), immune (immunoglobulins), and transport (hemoglobin, albumin). Unlike carbohydrates and fats, the body does not store surplus protein as a dedicated reserve — excess amino acids are deaminated and the carbon skeleton is either oxidised for energy or stored as glycogen and fat. This means protein intake must be consistently maintained rather than accumulated through periodic high-dose meals.
Of the 20 standard amino acids, nine are "essential" (cannot be synthesised de novo): histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Three branched-chain amino acids (BCAAs) — leucine, isoleucine, and valine — are particularly important for skeletal muscle metabolism, with leucine serving as the principal anabolic signal for muscle protein synthesis (MPS).
Recommended Daily Amounts by Population
Protein recommendations vary substantially by age, physiological state, and activity level. The table below synthesises current positions from the Institute of Medicine (IOM), the European Food Safety Authority (EFSA), and the International Society of Sports Nutrition (ISSN):
| Population | RDA / Minimum | Optimal Range | Notes |
|---|---|---|---|
| Sedentary adults (18–65) | 0.8 g/kg/day | 1.2–1.6 g/kg/day | RDA prevents deficiency; optimal supports lean mass preservation |
| Recreational exercisers | 0.8 g/kg/day | 1.4–1.7 g/kg/day | Higher end for resistance training days |
| Endurance athletes | 1.2 g/kg/day | 1.4–1.8 g/kg/day | Supports mitochondrial protein turnover and glycogen-sparing |
| Strength/power athletes | 1.4 g/kg/day | 1.6–2.2 g/kg/day | Upper range during caloric restriction (cutting phases) |
| Adults 65+ | 1.0–1.2 g/kg/day | 1.2–1.6 g/kg/day | Anabolic resistance requires higher per-meal leucine threshold |
| Pregnant women | +25 g/day above baseline | 1.2–1.5 g/kg/day | Critical for fetal tissue growth, especially second/third trimester |
| Caloric restriction (weight loss) | 1.2 g/kg/day | 1.8–2.7 g/kg/day | Higher protein preserves lean mass during energy deficit |
For a 70 kg moderately active adult, these ranges translate to approximately 84–119 g of protein per day — typically achievable through whole-food sources without supplementation.
Muscle Protein Synthesis and the Leucine Threshold
Muscle protein synthesis (MPS) is not a continuous linear response to amino acid availability — it operates in discrete "on/off" phases gated by leucine concentration in the bloodstream. Research from Moore et al. (American Journal of Clinical Nutrition, 2009) established that MPS in young adults plateaus at approximately 20 g of high-quality protein (equivalent to ~1.7–1.8 g leucine) per feeding, with minimal additional anabolic stimulus from higher single doses. Excess amino acids beyond this threshold are simply oxidised.
This leucine-threshold mechanism explains why protein distribution across meals matters as much as total daily intake. Older adults exhibit "anabolic resistance" — a blunted MPS response to the same leucine dose — requiring approximately 35–40 g of protein per meal (or 3.0+ g leucine) to achieve equivalent stimulation. This is a key physiological difference with profound implications for sarcopenia prevention.
Leucine content varies significantly across protein sources. Whey protein contains approximately 11% leucine by weight, making it highly efficient per gram for MPS stimulation. Soy protein contains about 8%, while wheat gluten contains only 7%. This partially explains why the DIAAS (Digestible Indispensable Amino Acid Score) has replaced the older PDCAAS method as the preferred protein quality metric.
Protein Sources and Quality Ranking
Both animal and plant sources can meet protein requirements, but their amino acid profiles and digestibility differ meaningfully. A well-constructed plant-based diet can achieve equivalent MPS to animal-based diets when total leucine intake is matched and digestibility differences are accounted for (van Vliet et al., Journal of Nutrition, 2015).
Animal Protein Sources
- Eggs: DIAAS 1.13 — considered the reference standard for protein quality; 6 g protein per large egg with excellent amino acid balance
- Whey protein (dairy): DIAAS 1.25; rapidly absorbed, peak plasma leucine at 60–90 minutes post-ingestion
- Chicken breast (cooked): ~31 g protein per 100 g; complete amino acid profile, low in saturated fat
- Salmon: ~25 g protein per 100 g with added omega-3 EPA/DHA; omega-3s may independently reduce muscle protein breakdown
- Greek yogurt: 17–20 g protein per 200 g serving; casein-dominant for sustained overnight amino acid availability
Plant Protein Sources
- Edamame/soybeans: Only complete plant protein; 18 g per 240 ml cup (cooked); DIAAS approximately 1.0
- Lentils: 18 g protein per 200 g cooked; lysine-rich, complementary to grains
- Chickpeas: 15 g per 200 g cooked; high in arginine supporting nitric oxide synthesis
- Hemp seeds: 10 g per 30 g serving; contains all essential amino acids, moderate DIAAS ~0.69
- Combination strategies: Rice + legumes or corn + beans achieve complete amino acid profiles through complementary pairing
Timing and Distribution Across the Day
The current consensus from the International Society of Sports Nutrition (ISSN Position Stand, Stokes et al., Journal of the International Society of Sports Nutrition, 2018) recommends distributing protein intake evenly across 3–5 meals to maximise 24-hour MPS. Practical examples:
- Breakfast: 3 eggs + 200 g Greek yogurt ≈ 35 g protein; activates MPS after the overnight fasting period
- Lunch: 150 g chicken breast + 200 g lentil soup ≈ 50 g protein
- Post-exercise: 20–40 g whey or equivalent within 0–2 hours of training; the "anabolic window" is broader than once thought — 2 hours pre- or post-workout is sufficient
- Pre-sleep: 30–40 g casein protein (e.g., cottage cheese, Greek yogurt) slows gastric emptying and sustains overnight MPS during the 7–8 hour fasting window; Snijders et al. (Journal of Nutrition, 2015) showed 12% greater overnight muscle protein accretion versus placebo
Total targets for a 75 kg person with moderate activity: ~120–135 g/day distributed across 3–4 meals of 30–40 g each maximises MPS efficiency.
Special Populations and Adjusted Needs
Older Adults and Sarcopenia Prevention
Skeletal muscle mass peaks around age 30 and declines approximately 3–8% per decade thereafter, accelerating after 60. Sarcopenia affects 10–15% of adults over 65 and up to 50% of those over 80, significantly increasing fall risk and all-cause mortality. Leucine-enriched protein supplementation combined with resistance training is the most evidence-supported strategy for attenuating age-related muscle loss. A minimum of 2.5–3.0 g leucine per meal is recommended for older adults to overcome anabolic resistance.
Plant-Based Diets
Vegans and vegetarians can meet all protein requirements through strategic food selection and higher total intake targets (approximately 10–15% above omnivore targets to compensate for lower digestibility). Key priorities: include edamame or other soy foods daily as a complete protein source, combine grains and legumes routinely, and consider leucine-enriched plant protein supplements if resistance training goals are ambitious.
Kidney Health Concerns
High protein diets in healthy individuals do not cause kidney disease. A systematic review of 28 clinical trials (Devries et al., JAMA Internal Medicine, 2018) found no evidence of adverse renal function with protein intakes up to 2.2 g/kg/day in people without pre-existing kidney disease. However, individuals with established chronic kidney disease (CKD stages 3–5) should follow clinician guidance on protein restriction, as their kidneys have reduced capacity to excrete nitrogen waste products.
Protein, Muscle Recovery, and NIR Light Support
Post-exercise muscle protein synthesis depends on both substrate availability (amino acids from dietary protein) and cellular energy status. Research on photobiomodulation suggests that near-infrared light at 800–850 nm may support aspects of the recovery process by modulating mitochondrial function in muscle tissue — the same cellular machinery that uses amino acids to rebuild contractile proteins (Hamblin, 2017).
While dietary protein provides the building blocks for muscle repair, adequate cellular energy production via ATP is required to drive the anabolic machinery. NIR light's proposed mechanism of displacing inhibitory nitric oxide from cytochrome c oxidase may transiently increase electron transport efficiency, potentially supporting the energy demands of post-exercise tissue repair. These effects should be viewed as part of a wellness routine, not as a substitute for adequate protein intake or professional care.
A practical recovery protocol combining both strategies might involve a protein-rich meal within 90 minutes of exercise, followed by an optional 10–15 minute NIR session targeting the primary muscles used, before a casein-rich pre-sleep meal to sustain overnight synthesis. Whether for daily cellular energy support or recovery-focused routines, this multi-modal approach reflects the growing recognition that nutrition and biophysical wellness strategies may be complementary rather than competing.
