Author's Note

This post has been updated again to reflect a more careful read of the underlying research. The protein quantity section previously treated the "1.6 to 2.2 g/kg" figure and the Morton et al. (2018) breakpoint behind it, as more settled than the primary literature supports; that section now flags where the data is genuinely contested rather than presenting a single number as definitive. The plant protein section has been substantially revised: it previously leaned on a single trial and a popular debate framing built partly on non-peer-reviewed sources, and now draws on multiple systematic reviews, including some published after the original framing, which complicate the picture in both directions. The practical recommendations are largely unchanged: 0.7–1.0 g/lb (1.6–2.2 g/kg) per day remains well-supported, distributed across 3–4 meals, with attention to source variety if you're plant-based. What's changed is how confidently specific numbers within that range are presented, and a closer match between what's cited and what the cited research actually found.

Summary

Protein is a macronutrient built from amino acids, essential for muscle repair, immune function, and enzyme activity. To maximize muscle protein synthesis (MPS), the process of building new muscle, you need resistance training plus adequate protein, particularly the amino acid leucine. For strength and muscle growth, aim for roughly 0.7 to 1.0 grams of protein per pound of body weight per day (1.6–2.2 g/kg), spread across 3 to 4 meals. Animal sources are naturally complete proteins, but plant-based eaters can meet their needs at an adequate total intake; the practical gap between sources is smaller than older fitness content suggests, though it isn't quite zero.

The basics

Protein is a macronutrient, like carbohydrate and fat, that the body needs in large amounts. It's built from amino acids linked into chains; there are 20 amino acids used to build human proteins, nine of which are essential, meaning your body can't make them, and you have to get them from food. Proteins do a lot: they're enzymes, transport molecules, antibodies, and structural material. For training purposes, the relevant job is repairing and building muscle tissue.

A complete protein has all nine essential amino acids in good proportions; most animal sources qualify, along with some plant sources like soy. An incomplete protein is short on one or more amino acids. Eating a variety of plant foods across the day covers the full amino acid profile, so vegetarians and vegans don't need to engineer "complete" meals.

Animal protein is generally more bioavailable than plant protein, meaning more of what you eat actually gets absorbed and used, but that gap depends heavily on which plant source you mean. Soy and potato protein digest about as well as many animal sources; wheat and most other grains digest meaningfully worse. Lumping all "plant protein" together overstates the problem.

Muscle protein synthesis (MPS)

MPS is the process your muscle cells use to build new protein and repair themselves after training. The primary trigger is mechanical tension from resistance training; dietary protein, and leucine specifically, supplies the raw material and acts as the chemical signal that switches the process on. A meal needs roughly 2.5 grams of leucine in younger adults (more in older adults, who need a bigger signal to get the same response) to fully trigger MPS, which works out to about 20–30 grams of high-quality protein per meal.

Chronically low calorie intake blunts MPS no matter how much protein you eat, which is why "just eat more protein" doesn't fix an undersized cut.

How much protein you actually need

The number you'll see everywhere is "1.6 to 2.2 g/kg/day," and it traces mostly to a 2018 meta-analysis by Morton and colleagues, which identified an apparent breakpoint around 1.62 g/kg, beyond which more protein didn't seem to help. That figure gets repeated as a settled fact more often than it deserves: it came from an unadjusted statistical model, and Morton's own fuller analysis (with adjustments for things like age and training status) didn't find protein dose significantly predicting muscle gains at all. The authors themselves flagged a wide margin of error around their number (1.03 to 2.20 g/kg) and suggested the upper end as the safer target.

A 2021 meta-analysis by Tagawa and colleagues, using a larger dataset and a different statistical approach, found no clean plateau at all, just steadily diminishing returns as intake rose past about 1.3 g/kg. And a 2022 analysis by Nunes and colleagues, published in the Journal of Cachexia, Sarcopenia and Muscle, found only a small overall benefit from added protein, and noted that most study subjects were already eating well above minimum levels before the trials even started, which muddies what "does more protein help" experiments are really testing.

None of this changes the practical recommendation much. 0.7–1.0 g/lb (1.6–2.2 g/kg) still sits comfortably inside the range every major analysis treats as adequate to generous. What it should change is your confidence in any single precise number you see floating around as if it's been nailed down. It hasn't.

If you're carrying more body fat than you'd like, base your target on a reasonable goal weight rather than your current weight; protein needs to be tracked with lean mass, not total mass.

Distribution and timing

Total daily intake predicts your results far better than when you eat it. Spreading protein across 3 to 4 meals of roughly 20–40 grams each is a sensible default, since each meal needs to clear that leucine threshold to do its job, but it's a secondary detail, not the main lever.

The "anabolic window," the claim that post-workout protein has to land within 30–60 minutes to count, isn't well supported. The real window is several hours wide, and it matters more if you trained fasted. If you eat before your workout, there's no rush.

A note on plant protein

The view that plant protein is meaningfully inferior for building muscle hasn't aged well, but it also hasn't fully disappeared, and the honest picture sits between the two extremes. A 2023 trial by Monteyne and colleagues put a high-protein, mycoprotein-rich vegan diet head-to-head against an omnivorous diet over 10 weeks of resistance training (matched at roughly 1.8–2 g/kg/day) and found statistically similar lean mass and strength gains in both groups. It's a small study built around a specific, unusually leucine-rich plant protein (Quorn-style mycoprotein), so it's better evidence that a well-built plant diet can match an omnivorous one than evidence that plant protein in general always does.

Two more recent systematic reviews complicate the "no difference" story. A 2021 review (Lim et al.) pooling 16 trials found no difference in absolute lean mass between plant and animal protein overall, but animal protein had an edge in younger trainees specifically. A 2025 review (Reid-McCann et al.) revisited the question with a different set of trials and found plant protein produced somewhat lower lean mass gains than animal protein, again concentrated in younger adults, though a separate 2025 review looking specifically at strength (rather than lean mass) found no meaningful difference between plant-based and omnivorous diets at all.

Put together: any gap that exists is modest, concentrated in lean mass more than strength, and easy to close. If you're plant-based:

• Lean on the higher-quality plant sources: soy (tofu, tempeh, edamame), and legumes paired with grains to round out the amino acid profile.
• Eat a bit more total protein than an equivalent omnivorous target, as a buffer; something like 10% more is a reasonable rule of thumb.
• Don't rely on a single plant source per day.

Key takeaways

• Protein is essential for muscle repair, growth, and immune function; nine amino acids must come from food.
• MPS is triggered primarily by training, with leucine (~2.5 g/meal) providing the chemical signal to build.
• 0.7–1.0 g/lb (1.6–2.2 g/kg)/day is a solid practical target, but treat the commonly cited "1.62 g/kg breakpoint" as a soundbite, not a settled number; the research behind it is more contested than it's usually presented.
• Total daily intake matters more than timing; 3–4 meals of 20–40 g is a reasonable structure, not a rule.
• The "anabolic window" is hours wide, not 30–60 minutes.
• Plant-based eaters can build muscle comparably to omnivores, with a modest, manageable gap in lean-mass gains (more so than strength) that closes with source variety and slightly higher total intake.

For the full evidence breakdown behind these numbers, including study details, effect sizes, and where the research disagrees with itself, see the deep-dive on Substack.

Bibliography

Lim, M. T., Pan, B. J., Toh, D. W. K., Sutanto, C. N., & Kim, J. E. (2021). Animal protein versus plant protein in supporting lean mass and muscle strength: A systematic review and meta-analysis of randomized controlled trials. Nutrients, 13(2), 661. https://doi.org/10.3390/nu13020661

López-Moreno, M., Rossi, E. V., López-Gil, J. F., Marrero-Fernández, P., Roldán-Ruiz, A., & Bertotti, G. (2025). Are plant-based diets detrimental to muscular strength? A systematic review and meta-analysis of randomized controlled trials. Sports Medicine - Open, 11(1), 62. https://doi.org/10.1186/s40798-025-00852-7

Monteyne, A. J., Coelho, M. O. C., Porter, C., Abdelrahman, D. R., Jameson, T. S. O., Jackman, S. R., Blackwell, J. R., Finnigan, T. J. A., Stephens, F. B., Dirks, M. L., & Wall, B. T. (2023). Vegan and omnivorous high protein diets support comparable daily myofibrillar protein synthesis rates and skeletal muscle hypertrophy in young adults. The Journal of Nutrition, 153(6), 1680–1695. https://doi.org/10.1016/j.tjnut.2023.02.023

Morton, R. W., Murphy, K. T., McKellar, S. R., Schoenfeld, B. J., Henselmans, M., Helms, E., Aragon, A. A., Devries, M. C., Banfield, L., Krieger, J. W., & Phillips, S. M. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine, 52(6), 376–384. https://doi.org/10.1136/bjsports-2017-097608

Nunes, E. A., Colenso-Semple, L., McKellar, S. R., Yau, T., Ali, M. U., Fitzpatrick-Lewis, D., Sherifali, D., Gaudichon, C., Tomé, D., Atherton, P. J., Robles, M. C., Naranjo-Modad, S., Braun, M., Landi, F., & Phillips, S. M. (2022). Systematic review and meta-analysis of protein intake to support muscle mass and function in healthy adults. Journal of Cachexia, Sarcopenia and Muscle, 13(2), 795–810. https://doi.org/10.1002/jcsm.12922

Reid-McCann, R. J., Brennan, S. F., Ward, N. A., Logan, D., McKinley, M. C., & McEvoy, C. T. (2025). Effect of plant versus animal protein on muscle mass, strength, physical performance, and sarcopenia: A systematic review and meta-analysis of randomized controlled trials. Nutrition Reviews, 83(7), e1581–e1603. https://doi.org/10.1093/nutrit/nuae200

Tagawa, R., Watanabe, D., Ito, K., Ueda, K., Nakayama, K., Sanbongi, C., & Miyachi, M. (2021). Dose-response relationship between protein intake and muscle mass increase: A systematic review and meta-analysis of randomized controlled trials. Nutrition Reviews, 79(1), 66–75. https://doi.org/10.1093/nutrit/nuaa104

For the methodological detail behind the contested figures above, including the Morton et al. meta-regression breakdown, the Nunes et al. critique-and-reply exchange, and full DIAAS sourcing, see the bibliography in the Substack deep-dive.