The research consensus
The Morton et al. (2018) meta-analysis is the most comprehensive analysis of protein and muscle growth to date, pooling data from 49 studies and 1,863 participants. The conclusion: protein intakes of approximately 1.6g per kilogram of body weight per day (0.73g per pound) maximize resistance training–induced gains in muscle mass and strength. This is the number that consistently emerges as the practical ceiling for meaningful benefit.
Benefits plateau beyond roughly 2.2g/kg/day (1.0g/lb). Eating more protein than this threshold is not harmful—excess amino acids are simply oxidized for energy or converted to glucose—but the additional muscle-building returns are negligible. For a 180 lb (82 kg) person, the optimal range translates to approximately 130–180g of protein per day. The lower end of that range captures most of the benefit; the upper end provides a safety margin for variability in protein quality, digestion, and individual response.
This does not mean the RDA of 0.8g/kg (0.36g/lb) is sufficient for muscle growth. The RDA is designed to prevent deficiency in sedentary individuals, not to optimize muscle protein synthesis in people who lift weights. The gap between the RDA and the evidence-based recommendation for trainees is substantial, which is why active lifters need to be intentional about their protein intake.
Per-meal protein: the 30–40g sweet spot
Muscle protein synthesis is triggered by the amino acid leucine. The threshold to maximize the MPS response is approximately 2.5 to 3g of leucine per meal, which corresponds to roughly 25–40g of high-quality protein (such as whey, eggs, or chicken). Below this threshold, MPS is stimulated but not maximized. Above it, additional protein in a single sitting still contributes to total daily intake but does not further increase the acute MPS response.
Macnaughton et al. (2016) demonstrated that 40g of whey protein post-exercise stimulated approximately 20% more muscle protein synthesis than 20g, particularly after full-body resistance exercise. This suggests that larger individuals or those performing high-volume training may benefit from the higher end of the per-meal range. For practical purposes, distributing your daily protein across 3 to 5 meals—each containing 25–40g—ensures you hit the leucine threshold multiple times per day and keep MPS elevated throughout your waking hours.
Best protein sources ranked
Not all protein sources are created equal. The key differentiator is leucine content per serving and overall bioavailability—how efficiently your body absorbs and utilizes the amino acids. Here are the top sources ranked by leucine content per typical serving:
- Whey protein isolate (25g serving): ~2.7g leucine — highest leucine density, fastest absorption
- Whole eggs (3 large): ~1.9g leucine — complete amino acid profile plus healthy fats
- Chicken breast (4 oz): ~2.3g leucine — lean, versatile, widely available
- Greek yogurt (1 cup): ~1.8g leucine — contains both whey and casein fractions
- Lean beef (4 oz): ~2.1g leucine — also provides creatine, iron, and B12
- Salmon (4 oz): ~1.9g leucine — omega-3 fatty acids support recovery and inflammation
- Tofu/tempeh (1 cup): ~1.4g leucine — lower bioavailability but solid plant option; combine with grains for complete amino acids
Animal proteins generally score higher on the PDCAAS (Protein Digestibility Corrected Amino Acid Score) and the newer DIAAS (Digestible Indispensable Amino Acid Score) scales because they contain all essential amino acids in proportions that match human requirements and are highly digestible. Plant proteins can absolutely support muscle growth, but you need to eat a variety of sources (legumes plus grains, for example) and aim for slightly higher total intake to compensate for lower digestibility and limiting amino acids.
Protein for different goals
- Fat loss with muscle retention: Increase protein to 2.0–2.4g/kg/day during a caloric deficit. Higher protein intake preserves lean mass, increases satiety, and slightly boosts the thermic effect of food. This is one of the most evidence-backed strategies for body recomposition.
- Endurance athletes: 1.2–1.6g/kg/day supports recovery and lean mass maintenance for runners, cyclists, and swimmers. The demands differ from strength training, but protein needs are still above the sedentary RDA.
- Older adults (50+): 1.2–1.6g/kg/day, with particular attention to per-meal intake of ~40g. Anabolic resistance—the blunted MPS response that comes with aging—means older adults need more protein per meal to achieve the same muscle-building stimulus as younger individuals.
- General fitness and health: 1.2–1.6g/kg/day covers most recreational exercisers who want to maintain lean mass and support recovery without obsessing over precise numbers.
Practical meal plan example
For a 180 lb (82 kg) person targeting 1.6g/kg = approximately 130g of protein per day:
- Breakfast: 3 eggs + 1 cup Greek yogurt = ~35g protein
- Lunch: 6 oz chicken breast + rice + vegetables = ~40g protein
- Post-workout: 1 scoop whey protein shake = ~25g protein
- Dinner: 5 oz salmon + roasted vegetables + quinoa = ~35g protein
- Daily total: ~135g protein
This example distributes protein across four eating occasions, each hitting or approaching the leucine threshold for maximal MPS. Adjust portion sizes up or down based on your body weight and goals. If you struggle to hit your target through whole foods alone, a protein supplement is a convenient and cost-effective way to close the gap. For specific protein powder recommendations, see our workout supplement guide. For help choosing between whey and casein, our whey vs casein comparison covers absorption timing and practical use cases. And if you want to round out your supplement stack, our creatine guide explains the other supplement with the strongest evidence base.
Frequently asked questions
Can you eat too much protein?
For healthy adults with normal kidney function, intakes up to 3.5g/kg/day show no adverse effects on kidney function, bone health, or cardiovascular markers (Antonio et al. 2016). A one-year crossover study found no harmful effects from very high protein diets. Excess protein beyond what your body uses for muscle repair is oxidized for energy—it is not preferentially stored as body fat. That said, there is no performance reason to go above 2.2g/kg/day for most people.
Do you need protein immediately after a workout?
The “anabolic window” is wider than the fitness industry originally claimed. Research shows that muscle protein synthesis remains elevated for several hours after training, not just 30 minutes. However, having a protein-rich meal or shake within 2 hours post-workout is still a reasonable and practical habit, especially if your last meal was several hours before training. The urgency matters less than consistency across the full day.
Can you build muscle on a plant-based diet?
Yes. Plant-based athletes can absolutely build muscle, but it requires more dietary planning. Combine multiple plant protein sources—such as legumes with grains, or soy with nuts—to ensure a complete essential amino acid profile in each meal. Aim for slightly higher total intake, around 1.8–2.0g/kg/day, to compensate for the lower digestibility and bioavailability of most plant proteins compared to animal sources. Soy protein isolate and pea protein are among the best plant options for leucine content.
Sources
- Morton RW et al., “A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength” (BJSM, 2018) — bjsm.bmj.com
- Macnaughton LS et al., “The response of muscle protein synthesis following whole-body resistance exercise is greater following 40g than 20g of ingested whey protein” (Physiological Reports, 2016) — physoc.onlinelibrary.wiley.com
- Antonio J et al., “A high protein diet has no harmful effects: a one-year crossover study” (JISSN, 2016) — jissn.biomedcentral.com
