Why protein comes up
When you eat less, you lose some lean mass as well as fat. In a SURMOUNT-1 body-scan substudy, about 26% of the weight lost on tirzepatide was lean mass (SURMOUNT-1 DXA substudy, 2025). Protein and strength training are the two things most often suggested to protect it (Joint nutrition advisory, Obesity, 2025). More on muscle loss.
What the guidance says
The 2025 joint advisory notes the US recommended allowance is 0.8 g per kg a day. It says higher targets of 1.2 to 1.6 g per kg a day have been proposed during active weight loss (Joint nutrition advisory, Obesity, 2025).
It also offers simpler targets: 80 to 120 g a day, or about 16 to 24% of your calories. It says intake shouldn't fall below 0.4 to 0.5 g per kg a day, and that staying at 2 g per kg or more for long periods is best avoided (Joint nutrition advisory, Obesity, 2025).
It warns that working it out from your full body weight can overestimate how much you need if you carry a lot of fat (Joint nutrition advisory, Obesity, 2025).
In the UK, Guy's and St Thomas' NHS Foundation Trust suggests 80 to 100 g of protein a day for most people on weight-loss medicines, with strength exercise twice a week (Guy's and St Thomas' NHS, 2025).
When to ask first
If you have kidney disease or another long-term condition, or you're not eating much at all, ask your doctor or a dietitian before changing how much protein you eat.
Make protein easier.
- Know roughly what you eat now
- Include protein at each meal
- Pair it with strength training
- Check in when appetite is very low
- Ask a dietitian for a personal target
Where these facts come from.
- Mozaffarian D et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society. Obesity 2025;33:1475-1503.
- Dietary advice for people taking weight-loss medicines: food and nutrition. Guy's and St Thomas' NHS Foundation Trust. Reviewed Aug 2025.
- Look M et al. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study of adults with obesity or overweight. Diabetes Obes Metab 2025;27:2720-2729.
Checked 25 Oct 2026. Trial figures are average results in the trial, not predictions. Labels change; your prescriber and the leaflet in your pack have the current version.
Pip Body Scan is a personal progress record. It is not a medical device and does not give medical advice, diagnose conditions or recommend doses. Speak to your prescriber or another qualified healthcare professional about symptoms, side effects or changes to your treatment.