GLP-1 protein calculator

Why protein comes up on a GLP-1

When weight comes off, some of it is lean mass. Lean mass on a DXA scan is everything that is not fat or bone, so it includes water and organs as well as muscle. Two body composition substudies measured it on the newer medicines:

The SURMOUNT-1 authors concluded that the share of lean mass lost on tirzepatide was similar to other ways of losing weight. The placebo group's split was almost the same. So these data do not show the medicine removing lean mass out of proportion. What changes is how much weight comes off and how hard it becomes to eat enough protein when appetite drops. No retatrutide body composition data are cited on this page.

The 2025 joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society answers with two things together: enough protein and strength training. It says GLP-1s should be prescribed with a structured exercise program that includes strength training at least three times a week. Protein on its own is not shown to prevent lean mass loss, which is why this calculator asks about training.

How the numbers are worked out

The range. The advisory notes that the general allowance is 0.8 g/kg a day and that higher targets of 1.2 to 1.6 g/kg a day have been proposed during active weight reduction. It also says intake should not fall below 0.4 to 0.5 g/kg a day and that prolonged intake at or above 2 g/kg a day should be avoided. The calculator shows 1.2 to 1.6 g/kg and never goes above it.

Where in the range. With strength training three or more times a week the calculator points to the top of the range, 1.6 g/kg. That matches a 2018 meta-analysis by Morton and colleagues, in which extra protein stopped adding lean mass gains from resistance training beyond about 1.6 g/kg a day. With one or two sessions it points to the middle (1.4) and with none to the bottom (1.2). These points are the calculator's convention inside the advisory's range, not a separate recommendation.

Which weight. The advisory says it is unclear whether targets for people with obesity should use actual, adjusted or ideal body weight or fat-free mass and that actual weight can significantly overestimate needs. So:

• Below a BMI of 30, or with no height entered, it uses your current weight.
• At a BMI of 30 or more it uses an adjusted body weight: ideal body weight (modified Devine formula: 50 kg for men or 45.5 kg for women, plus 0.91 kg per cm over 152.4 cm) plus 40% of the difference between that and your current weight. This is the convention in hospital weight-calculation references; the advisory itself does not settle on one method.
• If you enter a body fat percentage it uses 1.5 g per kg of lean mass, which the advisory calls more accurate when body composition data are available.

Per meal. The daily figure is split evenly across your meals. For comparison, Schoenfeld and Aragon's 2018 review suggested about 0.4 g/kg per meal over at least four meals for building muscle, a figure drawn from young resistance-trained adults eating enough overall. With a small appetite the calculator adds one protein snack so each sitting is smaller. The advisory's own tip applies too: eat the protein part of a meal first.

The flat alternative. The advisory also offers a fixed 80 to 120 g a day as a simpler target that may be easier to stick with. If your figure lands well outside that band, the calculator says so.

Protein in common foods

Per 100 g as eaten, from USDA FoodData Central: