Keeping muscle while you lose weight

What the trial scans found

Some participants in STEP 1 (semaglutide) and SURMOUNT-1 (tirzepatide) had DEXA body scans. In both, fat made up most of the weight lost, but lean mass accounted for a real share, roughly a quarter to two-fifths depending on the study.

That ratio is similar to what happens with diet-only weight loss. The drugs don't uniquely destroy muscle; they just make large losses happen faster.

Lean mass includes water and organs as well as muscle, so a DEXA lean number isn't purely muscle.

Why it matters

Muscle helps you stay strong, keep your balance and handle blood sugar. After about age 30, people slowly lose muscle each decade, a process called sarcopenia.

Losing more muscle than you need to can make it harder to keep weight off later, because muscle burns more energy at rest than fat. The BMR calculator shows how resting needs fall as you shrink.

The two habits with the best evidence

1. Strength training at least twice a week. Federal guidelines recommend muscle-strengthening work on 2 or more days, covering all major muscle groups. See exercise on a GLP-1.
2. Enough protein, spread across meals. Many clinicians aim for 1.0 to 1.5 grams per kilogram per day during weight loss. Use the protein calculator.

Research on protecting muscle during GLP-1 treatment specifically is still early. These recommendations come from wider weight-loss and aging research.

How to tell if you're losing muscle

The scale can't tell fat from muscle. Better signs:

• Your strength in the gym holds steady or rises
• Waist measurement drops faster than overall weight
• Daily tasks like stairs and carrying groceries stay easy
• A body composition test, such as DEXA, if your doctor orders one

Our body fat calculator uses tape measurements to track trends. It is an estimate, see how to measure body fat.

A starter strength routine

You don't need a gym to begin. Twice a week, do 2 to 3 sets of each move, stopping each set with 2 or 3 reps left in the tank:

1. Sit-to-stand or squat: 8 to 12 reps from a sturdy chair
2. Wall or counter push-up: 8 to 12 reps
3. Row: with a resistance band or a jug of water, 10 to 12 reps per side
4. Hip bridge: 10 to 15 reps lying on your back
5. Carry: walk 30 to 60 seconds holding grocery bags or dumbbells

Add reps, then weight, as moves get easy. Progress is the signal that you're keeping or building muscle. Once you're lifting heavier, the one-rep max calculator helps you track strength without testing a true max.

If you have joint problems or heart disease, ask your doctor first, and consider a few sessions with a physical therapist or certified trainer to learn form.

Older adults need extra care

If you are over 65, muscle loss carries more risk, including falls. Ask your doctor whether you need a slower pace of loss, a higher protein target or a referral to a physical therapist or registered dietitian.

When to call your doctor

• You feel new weakness, unsteadiness or have a fall
• Your strength drops noticeably over a few weeks
• You can't eat enough to meet even a basic protein target