In This Article
The short answer: Protein needs are not one number. Building muscle plateaus around 1.6 grams per kilogram of body weight per day, cutting fat while lifting benefits from a higher range near 2.3 to 3.1 grams per kilogram of fat-free mass, and healthy aging in older adults is better served by 1.0 to 1.5 grams per kilogram, with more needed during illness or injury. More protein is not automatically better once you are past the point where extra grams stop doing anything for your specific goal.
- What Protein Does
- Building Muscle
- Fat Loss
- Longevity
- Misconceptions
- How to Hit Your Number
- FAQ
- Key Takeaways
- References
Read key takeaways →
What Protein Actually Does, and Why the Dose Matters
Protein supplies the amino acids your body uses to build and repair muscle tissue, enzymes, and immune components. After resistance exercise, muscle protein synthesis (MPS) rises for roughly 24 to 48 hours as your body remodels tissue in response to the training stimulus. The amount of protein in a single meal changes how strongly that response fires, up to a point.
Daniel Moore and colleagues at McMaster University tested this directly by feeding young men whole egg protein after a resistance workout and measuring MPS at different doses. Synthesis rose progressively up to about 20 grams, then flattened out at 40 grams, with the extra amino acids increasingly burned for fuel rather than used to build tissue. That does not mean protein above 20 grams is wasted for the day, since digestion, other tissues, and overall nitrogen balance all use it. It does mean a single mega-dose meal is a less efficient way to hit a daily target than spreading intake out.
Muscle Protein Synthesis Response by Dose (Moore et al., 2009)
Meal distribution matters too. Madonna Mamerow and colleagues fed adults the same total daily protein either spread evenly across three meals or skewed toward dinner, then measured 24-hour MPS. The even distribution produced a stronger overall response. For more on how to spread intake across the day, see the protein timing guide, which covers the research on pre- and post-workout windows in more depth.
The Target for Building Muscle: About 1.6 g/kg, With Room Above It
The most complete answer for muscle gain comes from a 2018 meta-analysis and meta-regression by Robert Morton and colleagues, which pooled 49 randomized trials and 1,863 participants on protein supplementation during resistance training. Protein supplementation significantly increased strength and fat-free mass overall, but the meta-regression found that gains in fat-free mass stopped improving once total protein intake passed roughly 1.6 grams per kilogram of body weight per day. Below that point, more protein tracked with more muscle gained. Above it, extra protein did not add further benefit in the pooled data.
Practical Range for Muscle Gain
Below 1.6 g/kg/day
Likely leaving muscle gain on the table, especially for people newer to structured resistance training.
1.6 to 2.2 g/kg/day
The practical target range. It covers the point where extra gains stop, plus a margin for day-to-day variability in what you actually eat.
Above 2.2 g/kg/day
Not shown to add further muscle gain in the pooled trial data. Not harmful for a healthy person either, just not doing extra work for hypertrophy specifically.
Morton's meta-regression also found that training experience changed how much protein supplementation helped: more experienced lifters got more out of added protein than beginners, and older adults got less benefit than younger ones for a given dose, consistent with the reduced anabolic response to protein that comes with age.
The Target for Fat Loss While Keeping Your Muscle
A caloric deficit changes the math. When you are eating less than you burn, your body is more prone to breaking down muscle tissue for fuel alongside fat, and protein needs rise to counter that. Eric Helms and colleagues reviewed the evidence in lean, resistance-trained individuals dieting for a physique goal and concluded that protein needs during a deficit are likely 2.3 to 3.1 grams per kilogram of fat-free mass per day, scaled toward the higher end as the deficit gets more aggressive or the person gets leaner.
A randomized trial from Thomas Longland and colleagues put a version of this to the test directly. Forty young men trained hard (weights plus sprint intervals) while eating in a steep, roughly 40 percent energy deficit for four weeks, split into a higher-protein group (2.4 g/kg body weight per day) and a lower-protein group (1.2 g/kg body weight per day). The higher-protein group gained lean mass while losing fat over the four weeks; the lower-protein group lost some lean mass alongside its fat loss despite doing the same training. Total fat loss was substantial in both groups, but only the higher-protein diet also grew muscle during an aggressive cut.
Protein also has the highest thermic effect of the three macronutrients and is the most satiating gram for gram, which is a practical reason higher-protein deficits tend to be easier to stick with, independent of the muscle-preservation effect.
For most people cutting while lifting, that translates to roughly 1.8 to 2.7 grams per kilogram of total body weight per day, depending on how lean you already are. See the fat loss and muscle retention guide for how to combine that protein target with the rest of a cutting plan.
The Target for Long-Term Health and Healthy Aging
Protein needs rise again later in life, for a different reason than muscle building. Aging comes with anabolic resistance: older muscle needs a larger protein stimulus to trigger the same synthesis response that a smaller dose produces in a younger adult. The PROT-AGE Study Group, an international panel led by Jurgen Bauer and Yves Boirie, reviewed the evidence in 2013 and recommended that healthy older adults (roughly 65 and up) average at least 1.0 to 1.2 grams per kilogram of body weight per day, rising to 1.2 to 1.5 grams per kilogram for those managing an acute or chronic illness, to help maintain muscle mass and function.
PROT-AGE Targets for Older Adults
A frequently cited 2014 Cell Metabolism study by Morgan Levine and colleagues found, in a large observational NHANES cohort followed for 18 years, that high protein intake in the 50-to-65 age bracket was associated with higher overall mortality and cancer death, an association that was weaker or absent when the protein came from plant sources, while high protein intake in people over 65 was associated with lower mortality and cancer death. This is population-level associational data, not a controlled trial, so it cannot prove that protein itself caused those outcomes. Treat it as a reason to favor a mix of plant and animal protein sources in midlife rather than as a reason to avoid protein, especially given how directly the PROT-AGE trial evidence links adequate protein to preserved muscle in older age.
This is a big part of why muscle mass is one of the more useful longevity metrics to track: adequate protein intake is one of the few levers you control directly that supports keeping that muscle as you age.
The Biggest Misconceptions: Timing and Kidney Safety
Misconception: there is a narrow post-workout anabolic window. Alan Aragon and Brad Schoenfeld reviewed the nutrient timing literature in 2013 and found little support for the idea that protein must be consumed within a tight window after training to matter. Total daily protein intake, not the exact minute you eat it, is what the evidence best supports as the driver of muscle gain. A meal within a few hours of training is fine; skipping breakfast because you missed a 30-minute post-workout window is not something the research asks you to worry about.
Misconception: high protein damages healthy kidneys. Michaela Devries and colleagues pooled 28 studies and over 1,300 participants in a 2018 systematic review and meta-analysis and found that changes in kidney function (measured by glomerular filtration rate) did not differ between people eating higher- versus lower- or normal-protein diets. That finding applies to people with healthy kidneys; it does not apply to anyone with existing kidney disease, who should still follow a clinician's protein guidance.
How to Actually Hit Your Number
Pick the target range for your current goal
Roughly 0.8 g/kg for general health with no specific training goal, 1.6 to 2.2 g/kg for building muscle, 2.3 to 3.1 g/kg of fat-free mass for a lifting-supported fat loss phase, and 1.0 to 1.5 g/kg for healthy aging past 65.
Spread it across three to four meals
Aim for a moderate dose at each meal rather than one large dose. Twenty to forty grams per meal covers most body sizes and lines up with where the synthesis response levels off per sitting.
Weight your protein target to your training load
Rest days and heavy training days do not need dramatically different protein intake since the muscle remodeling window runs a day or two beyond the session itself.
Recheck your number when your goal or body weight changes
A protein target is a moving number, not a fixed one. Recalculate it when you shift from building muscle to cutting, or as body weight changes meaningfully in either direction.
Frequently Asked Questions
Is more protein always better for building muscle?
No. Morton and colleagues found in their 2018 meta-regression that fat-free mass gains from protein supplementation stopped improving past roughly 1.6 grams per kilogram of body weight per day. A target of 1.6 to 2.2 g/kg gives a practical margin above that point, but pushing well past it has not been shown to build more muscle.
Will a high-protein diet hurt my kidneys?
Not in people with healthy kidneys. A 2018 systematic review and meta-analysis by Devries and colleagues covering more than 1,300 participants found no difference in kidney function changes between higher- and lower-protein diets. This does not apply to people who already have kidney disease, who should follow their clinician's specific guidance.
Do I need to eat protein immediately after my workout?
No. Aragon and Schoenfeld's 2013 review of the nutrient timing literature found that total daily protein intake matters far more than eating within a narrow post-workout window. A meal within a few hours of training is plenty.
Is animal protein worse than plant protein for long-term health?
The evidence is more nuanced than a flat yes or no. An observational NHANES cohort study by Levine and colleagues (2014) associated high protein intake in midlife, particularly animal protein, with higher mortality and cancer risk, an association that was weaker with plant protein. That is population-level association, not a controlled trial, so it does not prove animal protein itself is the cause. A reasonable approach is mixing plant and animal sources rather than eliminating either.
How much protein should I eat in one sitting?
Research on the acute synthesis response, including Moore and colleagues' 2009 dose-response study, points to roughly 20 to 40 grams per meal as the range that maximizes the muscle protein synthesis response for most adults, with Mamerow and colleagues (2014) finding that spreading protein evenly across meals works better than skewing it toward one meal.
Should older adults eat more protein than younger adults for the same goal?
Generally yes. Aging brings anabolic resistance, meaning older muscle needs a larger protein stimulus to produce the same synthesis response. The PROT-AGE Study Group's 2013 recommendations of 1.0 to 1.2 g/kg/day for healthy older adults, rising to 1.2 to 1.5 g/kg/day during illness, sit above the general 0.8 g/kg reference intake used for younger, sedentary adults.
What to Remember
- →Protein targets differ by goal, not one universal number: about 1.6 to 2.2 g/kg/day for building muscle, 2.3 to 3.1 g/kg of fat-free mass for fat loss while lifting, and 1.0 to 1.5 g/kg/day for healthy aging past 65.
- →Morton and colleagues (2018) found that fat-free mass gains from added protein plateaued around 1.6 g/kg/day in a meta-analysis of 49 trials, so pushing well past that range has not been shown to build additional muscle.
- →During an aggressive fat loss phase, Helms and colleagues (2014) and a supporting randomized trial from Longland and colleagues (2016) both point toward higher protein intakes helping preserve or build lean mass while losing fat.
- →Older adults need more protein than younger adults for the same muscle-maintenance effect because of anabolic resistance, per the PROT-AGE Study Group's 2013 position paper.
- →The idea of a strict post-workout anabolic window is not well supported. Total daily protein intake matters far more than exact timing, according to Aragon and Schoenfeld's 2013 review.
- →High protein intake has not been shown to harm kidney function in healthy adults, based on a 2018 meta-analysis by Devries and colleagues, though people with existing kidney disease should follow individualized medical guidance.
Related on Protocol
What Protein Timing Actually Does for Muscle Repair and Recovery
How meal spacing and the leucine threshold affect muscle protein synthesis
Why Muscle Mass Is Your Best Longevity Metric (More Than Weight or BMI)
Why the protein target for older adults ties directly to long-term function
How to Use Your Wearable Data to Optimize Fat Loss Without Muscle Loss
Putting a higher-protein cutting target into a full fat loss plan
Track your protein intake against the goal that actually matters right now
Protocol logs your daily protein against a target built for your specific goal, whether that is building muscle, cutting fat, or supporting long-term health, instead of one generic number.
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Key Researchers
- Stuart Phillips (McMaster University) Exercise Metabolism Research Group. Senior author on much of the foundational dose-response and protein-timing research cited here.
- Eric Helms (Auckland University of Technology) Sports scientist whose systematic review established practical protein targets for lean, resistance-trained individuals dieting in a caloric deficit.
- Jurgen Bauer and Yves Boirie (PROT-AGE Study Group) Led the international panel behind the reference protein recommendations for older adults used by clinicians and dietitians.
Key Studies
- Morton et al. (2018) British Journal of Sports Medicine. Meta-analysis and meta-regression of 49 trials finding fat-free mass gains from protein supplementation plateau around 1.6 g/kg/day.
- Helms et al. (2014) International Journal of Sport Nutrition and Exercise Metabolism. Systematic review recommending 2.3 to 3.1 g/kg fat-free mass for lean, resistance-trained athletes in a caloric deficit.
- Longland et al. (2016) American Journal of Clinical Nutrition. Randomized trial finding a higher-protein diet preserved and grew lean mass during a steep energy deficit combined with intense training, compared with a lower-protein diet.
- Bauer et al. (2013), PROT-AGE Study Group Journal of the American Medical Directors Association. Position paper recommending 1.0 to 1.2 g/kg/day for healthy older adults and 1.2 to 1.5 g/kg/day during acute or chronic illness.
- Levine et al. (2014) Cell Metabolism. Observational NHANES cohort study associating high protein intake in midlife with higher mortality and cancer risk, and the opposite pattern after age 65.
- Mamerow et al. (2014) The Journal of Nutrition. Found that evenly distributing protein across meals produced a stronger 24-hour muscle protein synthesis response than skewing intake toward one meal.
- Aragon and Schoenfeld (2013) Journal of the International Society of Sports Nutrition. Review concluding total daily protein intake matters more than a narrow post-workout timing window.
- Moore et al. (2009) American Journal of Clinical Nutrition. Dose-response study finding muscle protein synthesis after resistance exercise plateaus around 20 grams of ingested protein per sitting in young men.
- Devries et al. (2018) The Journal of Nutrition. Systematic review and meta-analysis of 28 studies finding no difference in kidney function changes between higher- and lower-protein diets in healthy adults.
