Losing weight without losing muscle

Strength training is a central way to keep muscle while you lose weight: US guidelines say it can help maintain lean mass during weight loss.^{[1, 2]} Eating more protein than a standard diet adds a small extra benefit, and the official minimum is 0.8 g per kg.^{[3, 4]} A slower pace may help too: athletes aiming to lose 0.7% of body weight a week gained lean mass, while those aiming for 1.4% did not.^[5]

How much of the weight you lose is muscle?

Fat-free mass

Everything in your body that is not fat, including muscle, bone, organs and water. Studies of weight loss usually measure fat-free mass or lean mass, not muscle alone.

A widely cited rule says about one-fourth of weight lost is fat-free mass, and the rest is fat.^[6] A review of that rule found that lean losses with dieting tend to be small, and questioned how well studies measure them.^[6] Another review repeats the average of about 25% for dieting alone.^[7]

Exercise changes the picture. In 52 studies of middle-aged and older adults with overweight, 81% of diet-only groups lost fat-free mass equal to at least 15% of the weight they lost, compared with 39% of groups that dieted and exercised.^[8]

Some lean loss is not a disaster. A review found that diet-driven weight loss reduces muscle mass without hurting muscle strength, and that weight loss improves everyday physical function.^[9]

Still, it may matter for keeping weight off: in 57 adults, losing a larger share of fat-free mass was linked with more weight regain over the following 9 months.^[10] To see which kind of weight you are losing, read body fat percentage: scans, scales, calipers and the Navy method.

Strength training: the main tool

The Physical Activity Guidelines for Americans advise adults to do muscle-strengthening activities that work all major muscle groups on 2 or more days a week.^[1] They add that these activities can help maintain lean body mass during weight loss.^[1]

One trial put 160 older adults with obesity into a 6-month weight loss program plus aerobic training, resistance training or both, or into a control group.^[2] Every exercise group lost 9% of body weight.^[2] Lean mass fell 5% with aerobic training alone, 3% with both, and 2% with resistance training alone.^[2] Strength rose 18 to 19% in the groups that lifted, and 4% in the aerobic group.^[2]

Lifting reduces lean loss, but may not stop it. Across 65 trials in adults with overweight or obesity, resistance programs added 0.8 kg of lean mass on average, yet programs that combined lifting with eating less still saw lean mass fall.^[11] Aerobic exercise helps too: one review found both endurance and resistance exercise help preserve muscle during weight loss, and resistance exercise also improves strength.^[9]

If you want to track strength as you go, our one-rep max calculator estimates your max from any set you already do.

How much protein helps?

The recommended dietary allowance (RDA) for adults is 0.8 g of protein per kg of body weight a day, set by the Food and Nutrition Board of the National Academies, as summarized in Baum 2016.^[3] It was designed as the minimum needed to avoid losing body nitrogen.^[12]

Eating more than that while cutting calories helps, a little. Across 24 trials lasting about 12 weeks on average, higher-protein diets kept 0.43 kg more fat-free mass than standard-protein diets.^[4] In adults over 50, the gap was 0.45 to 0.83 kg, depending on how higher protein was defined.^[7]

Not every trial agrees. In 61 older adults with overweight on a 12-week diet, 1.7 g per kg did not keep more lean mass than 0.9 g per kg.^[13] A review found that short, tightly controlled studies show benefits. Longer studies are limited and conflicting, and sticking to the diet appears to be the main reason.^[14]

Several of the higher numbers come from people who lift. In a meta-analysis of strength training, protein above 1.62 g per kg gave no further gains in fat-free mass.^[15] That figure is about building muscle while training, and the authors note the break point was not statistically significant.^[15] For the full picture on protein, read how much protein you need.

Dalia's app offers three paces: 0.5, 1 or 1.5 pounds a week. For her, the 1 and 1.5 lb paces sit inside the 0.5 to 1% band in the worked example, and 0.5 lb sits below it. Protein targets in the app can be changed. A clinician or dietitian can help you pick one if any of the conditions below apply.

How fast should you lose?

Slower loss may protect lean mass, though the trials are small. In 24 elite athletes who lifted 4 times a week, those aiming to lose 0.7% of body weight a week gained 2.1% lean mass, while those aiming for 1.4% a week held steady.^[5] A review for natural bodybuilders suggests losing about 0.5 to 1% of body weight a week to keep the most muscle.^[19]

Results in people with overweight point the same way. In 57 adults who lost similar amounts, those on a 5-week very low calorie diet had a higher percentage of fat-free mass loss than those on a 12-week diet, 8.8% compared with 1.3%.^[10] Their weight regain was not different.^[10] In another small trial of 42 adults, body composition was more favorable after slow loss.^[20]

For safe weekly targets in general, see how fast you can safely lose weight, and for the whole plan, how to lose weight and keep it off.

When to talk to a clinician