Keeping more of your muscle while you lose weight
When you lose weight, you lose some lean mass along with fat. Strength exercise keeps more of it, and enough protein in the day helps a little.
Weight loss takes some lean mass
When you lose weight by eating less, part of what you lose is lean mass, and how much depends partly on what you do while you diet.
Studies measure lean mass, also called fat-free mass. It is everything in the body that is not fat, including muscle and water.[1]
A widely quoted rule says about a quarter of the weight lost is fat-free mass. A 2014 review of that rule calls it "at best an approximation". The share differs from person to person, and it changes over time.[1]
The same review, mostly of studies in Western adults with overweight or obesity, lists what affects how much of the weight lost is lean mass.[1]
- People who carry more body fat tend to lose a smaller share as lean mass.
- Bigger calorie cuts are linked to a larger share.
- Exercise added to a diet tends to shift more of the loss onto fat.
A 2017 review of trials in adults with obesity, young and old, looked at strength as well as muscle mass. It found that diet-led weight loss lowered muscle mass without harming muscle strength. Overall physical function, such as the ability to walk and climb stairs, improved.[2]
Strength work keeps more of it
In one US trial of frail older adults on a diet, those who did strength exercise lost less lean mass than those who did aerobic exercise only.
A 2017 trial in the US studied 160 frail adults aged 65 and over with obesity. Their average age was 70.[3] For 6 months, 3 groups followed the same diet, and each group also did a different kind of exercise: aerobic, strength, or both. A 4th group did not diet or exercise. No group dieted without exercise, so the trial compares kinds of exercise during a diet.[3]
In this trial, each dieting group lost about 9% of its weight. Lean mass fell in all 3 dieting groups, by different amounts.[3]
of lean mass lost with diet and strength exercise, in a US trial of 160 frail adults aged 65 and over with obesity.[3]
lost with diet plus strength and aerobic exercise together, in the same trial.[3]
lost with diet and aerobic exercise only, in the same trial.[3]
The strength group and the combined group did not differ clearly. Both lost less lean mass than the aerobic group.[3]
- The authors say strength work made the loss of lean mass and bone density smaller, but did not prevent it. They say the loss might be a harm, because it adds to the losses that come with age.[3]
- In the trial, strength rose by about a fifth in the 2 groups that lifted weights, while they lost weight. It stayed about the same in the aerobic group.[3] Everyday physical function improved most with strength and aerobic exercise combined.[3]
- Some people in the trial had muscle or joint injuries from the exercise.[3]
These were frail adults of 70 on average, so the results may not apply to a healthy person of 55.
The 2017 review found strength exercise an effective way to limit muscle loss during weight loss. Strength exercise also improves strength. The review calls the effect of aerobic exercise alone on muscle "uncertain".[2]
India's 2024 dietary guidelines say regular strength training with weights is necessary to maintain muscle mass.[4] What counts as strength work, and how often to do it, is set out in protein after 40.
If you have been inactive, or have a heart, joint or back problem, see a doctor before you start strength exercise.
If you get chest pain, or breathlessness that is new or worse than usual, stop and see a doctor.
Enough protein in the day
Too little protein while you diet makes the loss of lean mass worse, and whether extra protein helps is less clear.
The 2017 review says that eating too little protein while you diet makes the loss of lean mass worse.[2] Whether extra protein limits the loss is less clear. The review found conflicting results, and calls the benefit in a pooled analysis "very small but significant".[2]
- The review also found that extra protein does not improve strength.[2]
- Trials have not shown that spreading protein across your meals protects muscle during weight loss.[2]
India's 2024 dietary guidelines say a little more protein, about 15% of calories, may be important during a typical weight-loss diet. They describe that diet as 500 to 750 calories a day below what you need.[4] The guidelines advise against cutting more than 40% of your daily calories. Past that point, they say, protein is burned for energy and protects muscle less.[4]
Anyone who takes medicine for diabetes should check with their doctor before changing how much they eat. The same applies to blood pressure medicine.
The daily calorie and macro calculator shows the calories you need to keep your weight steady, and a daily protein figure. Ask your doctor how far below those calories to eat.
If you have kidney disease or have been told to limit protein, ask your doctor how much protein is right for you.
2 questions for your doctor
When you begin to lose weight, take these 2 questions to your doctor.
- Which strength exercise is safe for you to start?
- How much protein suits you?
If you lose weight you were not trying to lose, see a doctor.
Medical disclaimer: This article is general information. It does not replace advice from your doctor about your own health.
Common questions
Some of the weight you lose is lean mass. Lean mass is everything in the body that is not fat, including muscle and water. A 2014 review says the share differs from person to person and changes over time. Exercise added to a diet tends to shift more of the loss onto fat.
A 2017 review found strength exercise an effective way to limit muscle loss during weight loss. In a US trial of 160 frail adults aged 65 and over with obesity, 3 groups dieted, each with a different kind of exercise. The groups that did strength work lost less lean mass than the group that did aerobic exercise only. No group dieted without exercise. If you have been inactive, or have a heart, joint or back problem, see a doctor before you start strength exercise. If you get chest pain, or breathlessness that is new or worse than usual, stop and see a doctor.
India's 2024 dietary guidelines say a little more protein, about 15% of calories, may be important during a typical calorie-cutting diet. If you have kidney disease or have been told to limit protein, ask your doctor how much protein is right for you.
Sources
- Heymsfield SB, Gonzalez MC, Shen W, Redman L, Thomas D. Weight loss composition is one-fourth fat-free mass: a critical review and critique of this widely cited rule. Obes Rev. 2014;15(4):310-21. doi:10.1111/obr.12143. PMID: 24447775. Available from: pmc.ncbi.nlm.nih.govCited atBody Composition ApproachAbstract; ConclusionsForbes Approach; With Diet
- Cava E, Yeat NC, Mittendorfer B. Preserving Healthy Muscle during Weight Loss. Adv Nutr. 2017;8(3):511-519. doi:10.3945/an.116.014506. PMID: 28507015. Available from: pmc.ncbi.nlm.nih.govCited atAbstractEffects of exercise training; AbstractEffect of high-protein intakeEffect of high-protein intakeAbstractStrategies
- Villareal DT, Aguirre L, Gurney AB, Waters DL, Sinacore DR, Colombo E, et al. Aerobic or Resistance Exercise, or Both, in Dieting Obese Older Adults. N Engl J Med. 2017;376(20):1943-1955. doi:10.1056/NEJMoa1616338. PMID: 28514618. Available from: pmc.ncbi.nlm.nih.govCited atParticipants; Table 1InterventionBody Composition; Table 2Body Composition; Table 2Body Composition; Table 2Body Composition; Table 2Table 2DiscussionStrengthAbstractAbstract
- ICMR-NIN Expert Committee. Dietary Guidelines for Indians - 2024. Hyderabad: ICMR-National Institute of Nutrition; 2024. Available from: nin.res.inCited atp. 71, Guideline 10p. 66, Guideline 9p. 66, Guideline 9