Protein on a cut: bodyweight or lean body mass?

· 6 min read

The rule you've heard is "1 gram of protein per pound of bodyweight." It's repeated in every gym, on every forum, by every coach with a podcast. It isn't dangerous, but it isn't the target either. It's the top of the useful range, and for someone carrying a lot of fat it asks for far more protein than their muscle can use.

The fix has two parts. Use a range instead of one number, and measure that range against the right thing. For most people the right thing is plain body weight. Once body fat is high, it's lean body mass.

The two anchors

There are two ways to set a protein target. You pick a grams-per-kilogram figure, then multiply it by one of two things:

  • Total bodyweight. What the scale says. This is what "1 g per pound" uses (1 g per pound is about 2.2 g per kg of bodyweight).
  • Lean body mass. Everything in you that isn't fat: muscle, bone, organs, water. You get it from your weight and your body fat percentage.

Most protein research reports intake per kg of body weight. The 2017 ISSN position stand puts it at 1.4 to 2.0 g/kg of body weight a day for most people who exercise. So if you're in a normal body fat range, body weight is the anchor the evidence was built on, and you don't need a body fat number to use it.

Where bodyweight breaks

Fat tissue barely uses dietary protein. Muscle does. When fat is a modest share of your weight, body weight tracks your muscle well enough. When fat is a large share, body weight starts counting tissue that doesn't need the protein.

Take two men at the same 80 kg (176 lb), both lifting 3 to 4 times a week and cutting at the deficit Deficit suggests for them:

Lean (12% body fat) Higher fat (30% body fat)
Lean body mass 70.4 kg (155 lb) 56.0 kg (123 lb)
"1 g per pound" (2.2 g/kg bodyweight) 176 g 176 g
Deficit's target on a cut 140 g (1.75 g/kg bodyweight) 116 g (2.07 g/kg lean mass)

The lean man is at 12% body fat, so 88% of his weight is lean mass. Body weight is a fair stand-in for his muscle, and the target scales to it. He gets 140 g, which is about 0.8 g per pound.

The higher-fat man carries 24 kg (53 lb) of fat. The "1 g per pound" rule still hands him 176 g, because he weighs the same. That is over 3 g per kg of his lean mass. Scaled to his 56 kg of lean mass instead, his target is 116 g. That's protein his muscle can put to work. The rest of the 176 g would cost money, and room in a tight calorie budget, for no gain.

So the rule is simple. Below 25% body fat for men and 32% for women, protein scales to total body weight. At or above that line, it scales to lean body mass. The lean-mass range is higher per kg, 1.8 to 2.2 g/kg, because the number you multiply is smaller. For the 30% man that works out to 1.26 to 1.54 g per kg of body weight.

Cutting is when this matters most

A common question: do you need more protein when you're cutting than when you're maintaining? Often, yes, and never less.

When you eat at a deficit, your body has less energy to work with, and some of it can come from muscle. Protein is what helps offset that. Eat enough and the body holds on to more of your lean mass and burns more fat for the shortfall. Eat too little and more of the loss comes from muscle.

That's why a lifter's range on a cut sits higher than at maintenance: 1.6 to 2.2 g/kg of body weight instead of 1.4 to 1.8. For other kinds of training, and on the lean-mass basis, the range is the same for both goals, but a deep deficit moves you up inside it. A maintenance phase forgives a sloppy protein number. A deficit forgives it less.

The numbers that work

Three sources set the frame. The 2017 ISSN position stand finds 1.4 to 2.0 g/kg of body weight a day sufficient for most people who exercise. A 2018 meta-analysis by Morton and colleagues found that protein beyond about 1.62 g/kg a day gave no further gains in lean mass from lifting. And a 2014 review by Helms and colleagues suggests that lean bodybuilders dieting for a contest do best at 2.3 to 3.1 g per kg of lean body mass.

Deficit's ranges, in g per kg of the basis:

  • Cut, on body weight: strength training 1.6–2.2 (0.73–1.0 g/lb), strength plus sports 1.4–2.0, sports only 1.3–1.8.
  • Maintenance, on body weight: strength training 1.4–1.8, strength plus sports 1.4–2.0, sports only 1.3–1.8.
  • Lean mass basis (25%+ body fat for men, 32%+ for women): 1.8–2.2 g/kg of lean mass, for any training and any goal.

Inside a range, maintenance moves up with the number of workouts a week. A cut blends two things, half workouts and half deficit size. Deficits up to 20% don't raise the number. From 20% to 33%, the deficit part moves toward the top. A cut also never gets less protein than maintenance would at the same training. The protein calculator runs this rule for your own numbers.

How to work out your own number

Four steps:

  • Get your body fat percentage, even a rough one.
  • Below 25% (men) or 32% (women), your basis is body weight. At or above, it's lean body mass = weight × (1 − body fat % ÷ 100).
  • Pick a g/kg figure from the range for your goal and training.
  • Daily protein = basis in kg × that figure.

A worked example. An 80 kg (176 lb) man at 18% body fat lifts 3 to 4 times a week. He's below 25%, so his basis is his full 80 kg. On a cut his range is 1.6 to 2.2 g/kg. His training puts him a quarter of the way up. Deficit suggests a 21.5% deficit for him, and only the part above 20% counts, so it adds a little. He lands at 1.78 g/kg, or 142 g of protein a day (about 0.81 g per pound). At maintenance he'd get 133 g.

Now the same 80 kg man at 30% body fat. He's above 25%, so his basis is his 56 kg of lean mass and his range is 1.8 to 2.2 g/kg. On the suggested 27.5% cut, the formula gives about 2.0 g/kg, or 112 g. At maintenance with the same training it gives 2.07 g/kg, or 116 g. A cut never gets less than maintenance, so his target is 116 g.

If you don't know your body fat percentage, the body fat percentage calculator estimates it from a tape measure or skinfold calipers. The protein calculator gives your protein target, and the calorie deficit calculator gives your calories, protein and goal date together. The how Deficit works page lists the research behind each number.

If you can't measure body fat

You often don't need to. If you're clearly in a normal range, use body weight and the range for your goal. A rough guess is enough to tell which side of the line you're on. If you think you might be near or above 25% (men) or 32% (women), a tape-measure estimate is worth the five minutes, because that's where the basis changes and the target drops.

A few edge cases

  • Very lean lifters. Body weight is the basis, and it's close to lean mass anyway. The Helms review suggests 2.3 to 3.1 g/kg of lean mass for lean bodybuilders in contest prep. At 10% body fat, 2.2 g/kg of body weight is about 2.4 g/kg of lean mass, so the top of the cut range already lands in that band.
  • Higher body fat. The lean-mass anchor already pulls your number down. Don't add a bodyweight rule on top, or you'll be eating for fat you're trying to lose.
  • Plant-based diets. Plant proteins are digested a little less completely and tend to be lower in leucine, so aiming a bit higher inside your range is a reasonable hedge.
  • Older lifters. Muscle tends to respond less to each meal's protein with age, so the upper half of your range makes sense.

The takeaway

The 1 gram per pound rule isn't a scam. It's the top of the useful range dressed up as a law, and it gets less accurate the more fat you carry. For most people, scale protein to body weight and pick from the range for your goal: on a cut with lifting, 1.6 to 2.2 g/kg (0.73 to 1.0 g per pound). If your body fat is 25% or more (men) or 32% or more (women), scale it to lean mass instead, at 1.8 to 2.2 g/kg. On a cut, where the scale can't tell muscle from fat, that keeps the number tied to the tissue you're trying to protect. The scale weight vs body fat post covers the tracking side of that same problem.

Sources

Deficit is our iOS app. It handles all of this for you, and the first week is free.

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