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Nutrition

Muscle Preservation Calculator for GLP-1 Users

Losing weight fast is easy on a GLP-1. Holding onto muscle while you do it takes a protein floor, a deficit ceiling, and lifting. This works out all three from your own numbers.

Learn the details
How it's figured

Nothing here is about the medication. Every number is one that applies to anyone losing weight; what a GLP-1 changes is how easy it becomes to eat far too little without noticing. The protein floor is 1 gram per pound, the ceiling on weight loss is 0.7% of bodyweight a week, and the fiber target is 14 grams per 1,000 calories of what you actually eat rather than of maintenance.

Some lean mass loss is normal, and the headline number is scarier than it sounds

In the body composition substudy of the STEP 1 trial, people lost about 15 kg in total and roughly 45% of it was lean mass. That figure gets repeated as though 45% of the weight lost was muscle. It was not. Lean mass on a DXA scan includes water, organ tissue and the glycogen your muscles were holding, and losing some of all of that is what happens whenever a body gets meaningfully smaller. Researchers are openly split on how much of it is a problem. What is not disputed is that eating enough protein and lifting shift the ratio in your favour.

Why the ceiling is a rate, not a calorie number

A 300 calorie deficit is gentle for someone who is 250 pounds and severe for someone who is 130. Setting the limit as a percentage of your own bodyweight is what makes it mean the same thing to both. The 0.7% a week figure comes from a trial that compared exactly this: one group losing 0.7% a week, another losing 1.4%. The slower group added 2.1% lean mass while losing fat. The faster group held lean mass flat and saw testosterone fall.

The appetite suppression is the actual difficulty

Most people trying to lose weight are fighting to eat less. On a GLP-1 that fight is largely over, and a different one starts: hitting a protein floor and a calorie floor when very little food appeals. That is why this calculator gives you floors rather than targets to beat. Coming in under them is the failure mode here, not going over.

Fiber is calculated from what you eat, not from maintenance

The 14 grams per 1,000 calories guideline scales with intake, so eating considerably less food lowers the target rather than leaving you chasing the old one. At 2,400 maintenance calories the figure would be 34 grams; at a 1,700 calorie floor it is 24. That is still more fiber than most people manage, and getting it from food is where a lot of the digestive trouble on these medications quietly resolves.

What this calculator will not tell you

Anything about the medication. Not which one, not what dose, not whether to start, stay on it, or come off. Those are conversations for your doctor, and no number on this page is a substitute for one. What is here is the same nutrition and training guidance that applies to anybody in a deficit, arranged around the part a GLP-1 makes harder.

Sources: Garthe 2011, two rates of weight loss, Neeland 2024, lean mass on GLP-1 therapies, Academy of Nutrition and Dietetics on fiber

Tips

Two full-body lifting sessions a week does more for holding muscle than any of the eating numbers. In the trial the 0.7% figure comes from, every athlete lifted four times a week, and only the slower losers gained lean mass. Anything about your dose, your side effects, or whether to keep taking it belongs with your doctor.

Common questions

How much protein should I eat on a GLP-1?
One gram per pound of bodyweight a day, treated as a floor rather than a target to beat. At 200 pounds that is 200 grams. The number is not special to the medication, it is what anybody trying to keep muscle through a deficit is aiming at. What changes is that hitting it takes planning once food stops appealing, so I would build the day around protein first and let the rest fill in behind it.
How fast is too fast to lose weight?
Losing more than about 0.7% of your bodyweight a week is where it starts to cost you. In Garthe 2011, athletes losing at that rate gained lean mass while losing fat, and a group losing twice as quickly did not. At 220 pounds, 0.7% is roughly 1.5 pounds a week. Read it as a ceiling, not a goal, and coming in slower than it is completely fine.
Will I lose muscle as well as fat?
Some of any real weight loss is lean tissue, and that is true of every deficit rather than anything specific to a medication. The 2024 Neeland review of lean mass on GLP-1 therapies lands on the same levers as the wider weight loss literature: protein, resistance training, and how fast the weight is coming off. Those three decide the ratio, which is why this page works them out for you.
Do I need to lift weights, or is eating enough?
Eating well protects muscle, but lifting is what gives your body a reason to keep it, and the two are not interchangeable. Two full-body sessions a week is the floor worth aiming at, and it is the highest-leverage habit on this page. Walking and cardio are worth doing for plenty of other reasons, they just will not do this particular job.