- Without strength training, a large share of weight lost can be muscle.
- Lift weights two to three times a week and eat enough protein; these two matter most.
- Lose weight at a moderate pace, about 0.5 to 1% of body weight a week.
- Muscle protection matters more with age and on GLP-1 medicines like semaglutide.
The goal of weight loss is to lose fat, not muscle. Muscle keeps you strong, supports metabolism and blood sugar control, and protects against frailty as you age. This guide covers how to keep it.
Why weight loss costs muscle
In a calorie deficit, the body breaks down some muscle for energy, especially if protein is low and muscles aren’t being challenged. Fast weight loss and very low-calorie diets increase the share of muscle lost.
The four essentials
- Strength training: two to three full-body sessions a week, with progressively heavier weights
- Protein: about 1.2 to 1.6 g/kg of body weight, more if training hard, spread over meals
- A moderate deficit: lose about 0.5 to 1% of body weight per week
- Sleep: 7 to 9 hours; short sleep shifts weight loss toward muscle
Weight loss medicines
People losing weight on GLP-1 medicines such as semaglutide lose some lean mass along with fat. Because appetite is very low, protein intake often falls short. Strength training and deliberate protein targets help protect muscle. See our semaglutide guide.
Older adults
Muscle loss with age (sarcopenia) speeds up after about 50, and weight loss can accelerate it. Canadian activity guidelines recommend muscle-strengthening activities at least twice a week for adults, and older adults benefit from balance training too.
Tracking
The scale can’t tell fat from muscle. Track waist measurements, strength in your main lifts, and progress photos. If strength drops steadily, increase protein or slow the rate of loss.
Frequently asked questions
How do I lose fat without losing muscle?
Strength train two to three times a week, eat enough protein, lose weight at a moderate pace and sleep well.
How much protein do I need to keep muscle?
About 1.2 to 1.6 g per kg of body weight, more if you train hard.
Does semaglutide cause muscle loss?
Some lean mass is lost with the fat; strength training and protein help protect muscle.
Is cardio bad for muscle?
No, in reasonable amounts. Strength training is what protects muscle.
This article is general information for adults in Canada, not medical advice. Talk to a doctor or pharmacist before using any prescription drug, anabolic steroid or research compound, and get bloodwork done. If you’re in crisis, call or text 9-8-8 (Suicide Crisis Helpline) any time.
