How much protein you actually need

That figure marks the point where muscle gains stopped rising in a large review of weight training trials. Everything else here builds on it.

Its authors pooled 49 trials with 1,863 people who lifted for at least 6 weeks, some taking protein supplements and some not.¹ On top of what lifting alone produced, supplements added about 300 grams of muscle and a few kilograms to people's one-rep max.

Next they asked how muscle gains changed with total daily protein. Gains kept climbing up to that figure and flattened after it. The uncertainty around it was wide, from about 1 gram to just over 2 grams per kilogram.¹ Treat it as the best guess we have, not a hard line.

Who was lifting mattered as well. Supplements were more effective in experienced lifters than in beginners, and their effect shrank steadily with age.¹

Bottom line

The number is where extra protein stopped adding muscle across 49 lifting trials.

In the US, the official recommended amount for adults, 0.8 g/kg a day, is a floor for avoiding a shortage.² It isn't a target for building muscle.

Figures like it come from studies that measured how much nitrogen, a part of every protein, people took in and lost. A 2003 analysis of 19 such studies with 235 people put the average need at about two-thirds of a gram per kilogram.³ The amount that covers nearly everyone came out slightly higher, close to the official allowance.

Groups that focus on exercise set the bar higher. The International Society of Sports Nutrition is a professional society for the field. It recommends 1.4 to 2 grams per kilogram a day for most people who exercise.⁴

Older adults need more than the floor too. In 2013, an international expert group called PROT-AGE recommended at least 1 to 1.2 grams per kilogram for people over 65.⁵ It advised a little more for those who exercise.

Bottom line

The official allowance keeps you out of shortage. Building muscle takes about twice as much.

The main exception to the ceiling is a hard diet. When you eat well below your needs, higher protein helps you keep muscle while you lose fat.

In a 2016 trial, 40 young men ate about 40 percent fewer calories than they needed for 4 weeks and trained six days a week.⁶ Half ate twice as much protein as the other half.

The sports nutrition society makes the same call for trained lifters on a diet.⁴ It suggests 2.3 to 3.1 grams per kilogram a day while cutting.

Bottom line

On a steep calorie cut, going well above the usual target is worth it. At maintenance, it mostly isn't.

Above the range where gains level off, additional protein doesn't add muscle. It adds calories, and in one trial it didn't even add fat.

In a 2014 study, 30 trained men and women were split into two groups for 8 weeks.⁷ One group ate about 307 grams of protein a day, more than four grams per kilogram, while the control group ate about 138 grams. The high-protein group ate more calories too, yet their body weight, fat and muscle didn't change compared with the control group.

Worry about kidney damage is a common reason people hold back on protein. A 2018 review pooled 28 trials with 1,358 healthy adults.⁸ It tested diets with at least 100 grams of protein a day, or a similar amount for body size. Those diets didn't harm kidney function.

The review covered people without kidney disease, so anyone with a kidney condition needs their own doctor's advice.

Not every expert stops at the review's ceiling. Peter Attia, a physician and the author of the longevity book Outlive, treats it as a minimum.² For active people he suggests starting at 1 gram per pound of body weight, which works out to about 2.2 grams per kilogram. The trials above suggest the extra mostly becomes calories, and the kidney review suggests his higher number is unlikely to hurt a healthy person.

Bottom line

Past about 2 grams per kilogram, more protein buys you calories rather than muscle, unless you're cutting hard.

Your daily total matters most, and splitting it across three or four meals of 20 to 40 grams is a sensible way to reach it.⁴

The International Society of Sports Nutrition suggests 20 to 40 grams of high-quality protein per meal, spaced every 3 to 4 hours.⁴ An older study gave six young men different amounts of egg protein after a leg workout.⁹ Twenty grams was enough to max out muscle building, and forty grams added nothing more.

A 2023 study in healthy young men challenged that ceiling.¹⁰ After a full-body workout, 100 grams of protein produced a larger response that lasted more than 12 hours, compared with 25 grams.

In practice, the two findings don't conflict as much as their headlines suggest. If your daily total is right, the size of each serving matters less than the early studies suggested.

Bottom line

Hit the daily total first. Three or four servings of 20 to 40 grams is the easy way there.

1. 01

   About 1.6 g/kg a day is where extra protein stopped adding muscle in 49 lifting trials.

2. 02

   The official allowance avoids a shortage, and people who train need about twice that.

3. 03

   During a steep calorie cut, 2.3 to 3.1 g/kg may help you keep muscle.

4. 04

   Past about 2 g/kg at maintenance, extra protein mostly adds calories.

5. 05

   Spread your protein across three or four meals of 20 to 40 grams.