Macros to keep muscle while losing weight: a body recomposition guide for men

On a calorie-reduced diet alone, people with overweight or obesity typically lose about 20% to 30% of the weight as fat-free mass, not fat. [1] Fat-free mass is everything that is not fat: mainly muscle, bone, organs and water.

Two things change that share. The first is protein at 1.2 to 1.6 g per kilogram of body weight a day. [2] The second is strength training at least twice a week. [1] [3]

Training matters more than any macronutrient, as the trials below show. Protein helped at the margin [4] and the size of the deficit mattered. [5] No trial we found set a carbohydrate or fat level for muscle once protein was in place. [4] [6]

Macros, short for macronutrients, are the three nutrients that supply energy: protein, carbohydrate and fat. This article sets out what the evidence shows about keeping muscle while losing weight.

Every figure is a group average from a study, not a prediction for any one man. The study populations are named so you can judge how far they apply to you.

How much muscle do you lose when you diet?

About 20% to 30% of what you lose, if diet is all you change. A 2017 review found that fat-free mass contributes about 20% to 30% of total weight loss in people with overweight or obesity. [1] In people of normal weight the share often exceeds 35%. [1]

Men tend to lose more fat-free mass than women, especially soon after starting, probably because they start leaner. [1] After an 8% to 10% weight loss, studies in men and women with obesity measured a 2% to 10% fall in muscle mass. [1] The review authors read most of that as muscle settling to a lighter body, because people with obesity carry more muscle to begin with. [1]

What happens when exercise is added?

A review of 52 studies in adults aged 50 and over with a BMI above 25 compared diet alone with diet plus exercise. In 81% of the diet-only groups, 15% or more of the weight lost was fat-free mass. With exercise added, mainly aerobic, that figure fell to 39%. [7]

BMI is body mass index, weight in kilograms divided by height in metres squared. The authors said the findings suggest exercise is an effective tool for preserving fat-free mass after moderate diet-induced weight loss in that age group. [7] The review covered men and postmenopausal women aged 50 and over, so apply it to younger men with care.

What does protein do during a deficit?

Protein shifts the loss towards fat and away from lean mass, modestly. Lean mass is what the trials call fat-free mass: everything that is not fat. A meta-analysis pooled 24 randomised trials with 1,063 adults on energy-restricted diets that matched calories and fat but differed in protein.

A meta-analysis combines the results of many trials into one estimate. [4]

Over an average of 12 weeks, the higher-protein groups kept 0.43 kg more fat-free mass, lost 0.87 kg more fat and 0.79 kg more weight. [4] Their resting energy expenditure also fell less, by 595.5 kJ a day. [4] The authors called every one of these benefits modest. [4]

How much protein, in grams?

A 2015 review of the trial evidence pointed to 1.2 to 1.6 g of protein per kilogram of body weight a day during weight loss. [2] The same review pointed to about 25 to 30 g at each meal. [2] That is a trial range, not UK guidance.

The UK reference nutrient intake is 0.75 g per kilogram, a figure set to prevent deficiency rather than to protect muscle. [8]

The 2017 review frames it as a multiple of the US recommended dietary allowance, which is 0.8 g per kilogram. It gives 1.25 to 1.5 times that for people who are sedentary. [1] For people who exercise, it says more than 1.5 times. [1]

The 2017 review also warns that eating below that allowance costs fat-free mass even without a deficit, and adds to the loss during one. [1] For a calculator that works the range out from your weight, see how much protein you need to lose weight.

What did the trial in young men find?

One randomised trial tested a very high intake in 40 young men with overweight, average age 23 and BMI about 29.7. [6] For four weeks they ate 40% below their energy needs and trained under supervision six days a week, with all food provided. Half ate 1.2 g of protein per kilogram a day and half ate 2.4 g. [6]

The higher-protein group gained 1.2 kg of lean mass and lost 4.8 kg of fat. The lower-protein group held lean mass steady, up 0.1 kg, and lost 3.5 kg of fat. [6] Strength and fitness improved equally in both groups. [6]

Two cautions. The men were young, not resistance trained and supervised six days a week, with protein drinks spread through the day. [6] That is not an ordinary week.

The 2.4 g figure is also far above the trial range. The authors themselves noted that lean mass held even at 1.2 g per kilogram. [6]

Is there an upper limit worth knowing?

In people who were not dieting, extra protein stopped adding muscle above about 1.6 g per kilogram a day. That comes from a meta-analysis of 49 resistance-training trials with 1,863 healthy adults, average age 35. [9] Protein supplements added 0.30 kg of fat-free mass to what training alone produced, a 27% increase, and 2.49 kg to one-repetition strength, a 9% increase. [9]

The 1.6 figure is a statistical break point with a wide margin, from 1.03 to 2.20 g per kilogram. [9] Those trials excluded people in an energy deficit, so treat it as a ceiling for building muscle, not a rule for dieting. [9] The 2017 review recommends adequate but not excessive protein. [1]

Why does strength training matter more than any macro?

Because training is the stimulus that tells muscle to stay. In the 49-trial analysis, training alone added 27 kg to people's one-repetition maximum, the heaviest weight they could lift once. [9] Extra protein added 2.49 kg on top. [9]

The authors called training a far more potent stimulus for strength than protein supplementation. [9] During weight loss, the 2017 review reported that progressive resistance training alongside a reduced-calorie diet attenuated muscle loss in middle-aged and older men and women. [1] Its reading is that resistance exercise can attenuate or even prevent weight-loss-induced muscle loss, while the effect of endurance exercise on muscle is uncertain. [1]

What does UK guidance say?

The UK Chief Medical Officers advise muscle-strengthening activities on at least two days a week, working all the major muscle groups. [3] They advise it alongside 150 minutes of moderate activity. [3] They say strength work should be considered as important as the 150 minutes, and that any strengthening activity is better than none. [3]

The NHS lists lifting weights, resistance bands, body-weight exercises such as push-ups, heavy gardening and carrying heavy shopping as strengthening activities. It says to work to the point where you need a short rest before repeating the activity. [10] Strength work is not a substitute for the 150 minutes of aerobic activity. [10]

How big a deficit, and how fast?

Smaller and slower keeps more muscle, in the studies that tested it. A meta-analysis of resistance-training trials found that training in an energy deficit impaired lean mass gains but not strength gains. [5] Its statistical model estimated that a deficit of about 500 kcal a day was enough to cancel the lean mass gain training would otherwise produce. [5]

The authors advised people losing weight to train and to keep the deficit at or below 500 kcal a day to maintain lean mass. [5] The analysis did not model protein intake. [5]

The people in those analyses were mostly sedentary women with an average age of 51 to 60. The deficit groups had a BMI of about 33. [5] That makes the figure a guide for men rather than a measurement in them.

What about the rate of loss?

Two small trials point the same way. In 24 elite athletes doing four strength sessions a week, losing 0.7% of body weight a week increased lean mass by 2.1%. Losing it faster, at about 1% a week against a planned 1.4%, left lean mass unchanged. [11]

Those were athletes, not men managing their weight.

What did the slow-versus-fast trial find?

The second trial studied 36 inactive adults with a BMI of 32 to 34, 72% of them women. Losing about 6% of body weight over 15 weeks cost 0.52 kg of lean body mass. [12]

Losing the same amount over 5 weeks cost 1.51 kg, and the slower group lost more fat. [12] The trial measured body composition by bioelectrical impedance, a small electrical current passed through the body, and included no exercise. [12]

The high-protein group in the four-week trial went from 100.1 kg to 94.2 kg, about 1.5% a week by our arithmetic from the trial's table. [6] The lower-protein group went from 96.0 kg to 92.5 kg, about 0.9% a week. [6]

The high-protein men still gained lean mass with daily training. [6] So deficit size, protein and training work together.

The NHS advice is a steady 0.5 to 1 kg a week. [13]

How should you spread protein across the day?

Evenly, at roughly 30 g a meal, on the evidence available. A feeding study of 8 healthy adults compared about 30 g at each of three meals with a pattern of 11, 16 and 63 g. [14] The even pattern produced a 24-hour muscle protein synthesis rate 25% higher than the other. [14]

Both patterns gave about 90 g a day, which was 1.2 g per kilogram. [14] Muscle protein synthesis is the rate at which the body builds new muscle protein. The study was small and the participants were not losing weight. [14]

The 2017 review suggests an even spread may help, and adds a caution.

Two randomised trials in middle-aged and older adults found no benefit of an even spread for keeping fat-free mass during weight loss. [1] The question has not been tested directly. [1] How much one meal can use is debated.

The feeding study's authors cite about 30 g of high-quality protein as the amount that maximally stimulates synthesis in healthy adults. [14] The 2017 review puts the plateau at about 20 g. [1] The weight-loss review's 25 to 30 g a meal sits between the two. [2]

For portions that reach it, see high-protein foods for weight loss.

Do carbohydrate and fat matter for keeping muscle?

Less than protein and training do, on the evidence available. In the 24-trial meta-analysis, the higher-protein diets were lower in carbohydrate with fat held equal, and they preserved more fat-free mass. [4]

In the trial of young men, carbohydrate was fixed at 50% of energy in both groups. [6] The higher-protein group got there by eating 15% fat instead of 35%. [6]

Neither result sets a carbohydrate floor or a fat figure for muscle. No source we found names one. The practical reading is to set protein first, then divide the remaining calories between carbohydrate and fat in the way you can sustain.

Fat still has a ceiling: UK guidance keeps it at no more than 35% of food energy, with saturated fat no more than 11%. [15] The macro calculator applies both while leaving the balance to you.

What is body recomposition, and is it realistic?

Body recomposition means losing fat and gaining or keeping muscle at the same time. The trials show it can happen under certain conditions.

The young men on 2.4 g of protein per kilogram gained 1.2 kg of lean mass while losing 4.8 kg of fat in four weeks. [6] They trained under supervision six days a week. [6] The athletes losing 0.7% a week gained 2.1% lean mass while losing 5.6% of their body weight. [11]

Both results came with a supervised resistance-training programme. Even with training, the pooled trials show that a deficit of about 500 kcal a day removed the lean mass gain.

Larger deficits cost lean mass. [5] Without training, the faster group in the 15-week trial lost more lean mass. [12]

For most men managing their weight, holding muscle while fat falls is the realistic version. The men who gained muscle in the four-week trial were not resistance trained before it. [6]

The deficit meta-analysis had too little data on experienced lifters to say. [5] Keeping the deficit at or below 500 kcal a day is the one condition the sources name. [5]

How can you tell if you are keeping muscle?

The scales cannot tell you. Weight falling at 0.5 to 1 kg a week says nothing about what the kilograms were made of. [13] Two signs tell you more than the scales, though neither measures muscle.

The first is strength: in the trials, strength held or rose even while weight fell. [5] [1] Diet-induced weight loss did not reduce leg strength or reduced it only slightly. [1]

If the weights you lift are holding or going up while your waist shrinks, your strength is holding. The 2017 review found diet-induced weight loss reduces muscle mass without adversely affecting strength, so lifts track function, not muscle mass. [1]

If your lifts fall week on week, look at the deficit and the protein. The second sign is function: grip strength, walking speed and stair climbing improved after weight loss in the studies reviewed. [1]

Body composition scales that pass a current through the body give a rough estimate. The 15-week trial used one. [12] Treat differences of about a kilogram with caution and track the trend over months rather than any single reading.

Frequently asked questions

Can you build muscle while losing weight?

Yes, in the right conditions. Young men with overweight gained 1.2 kg of lean mass in four weeks on a 40% deficit, with high protein and daily supervised training. Elite athletes gained 2.1% lean mass losing 0.7% of body weight a week.

It is harder than keeping muscle. In pooled trials, a deficit of about 500 kcal a day cancelled the lean mass gain from training, mostly in sedentary older women.

How much protein do I need to keep muscle while dieting?

The weight-loss review pointed to 1.2 to 1.6 g per kilogram of body weight a day, with about 25 to 30 g a meal. For a 90 kg man that is 108 to 144 g a day.

Above about 1.6 g per kilogram, extra protein did not add muscle in people who were training without a deficit. The UK reference intake of 0.75 g per kilogram is a baseline against deficiency, not a muscle-keeping figure.

Do I need protein shakes or supplements?

No. The pooled benefit of protein in the training trials came from studies using whey, casein, soy, pea, milk, whole foods and blends. What tracked the gains was the daily total, not the form.

None of the sources we found calls for branched-chain amino acid (BCAA) supplements. Food can reach 25 to 30 g a meal. A shake is a convenience, not a requirement.

Does cardio cost you muscle?

Not on the evidence here. In the 52-study review of older adults, the exercise groups were mainly aerobic and preserved fat-free mass better than diet alone. The 2017 review calls the effect of endurance exercise on muscle during weight loss uncertain rather than harmful.

Resistance training has the clearer effect on muscle. UK guidance asks for both: 150 minutes of aerobic activity and strength work on two days.

Should older men eat more protein?

The UK reference intake has not been raised for older adults. In the training trials, protein supplements became less effective with age. The natural decline in muscle and bone starts from around 50.

That makes strength training more important with age, not less. The trial range of 1.2 to 1.6 g per kilogram still applies during weight loss. If you have kidney disease, ask your GP or dietitian first.

Does losing muscle slow your metabolism?

Resting energy expenditure falls with weight loss on any diet. In the 24-trial meta-analysis, higher-protein diets softened that fall by 595.5 kJ a day, about 140 kcal. The authors called that modest.

In the slow-versus-fast trial, resting metabolic rate fell less in the slower group. Higher protein and a slower rate of loss softened the fall at the margin. Neither stopped it.

HeMed provides clinician-led weight management. This page is general health information, not medical advice. If you are worried about symptoms, speak to your GP, or use NHS 111.

Next step: see what the HeMed blood test measures.

Sources (15)

1. Cava E, Yeat NC, Mittendorfer B. "Preserving healthy muscle during weight loss". Advances in Nutrition 2017;8(3):511 to 519. Full text. pmc.ncbi.nlm.nih.gov/articles/PMC5421125. Accessed 28 October 2026.
2. Leidy HJ and colleagues. "The role of protein in weight loss and maintenance". American Journal of Clinical Nutrition 2015;101(6):1320S to 1329S. Abstract. doi.org/10.3945/ajcn.114.084038. Accessed 28 October 2026.
3. Department of Health and Social Care, "UK Chief Medical Officers' physical activity guidelines", published 7 September 2019, last updated 10 July 2026, sections "Adults (19 to 64 years)" and "Adults guidelines". gov.uk/government/publications/physical-activity-guidelines-uk-chief-medical-officers-report. Accessed 28 October 2026.
4. Wycherley TP and colleagues. "Effects of energy-restricted high-protein, low-fat compared with standard-protein, low-fat diets: a meta-analysis of randomized controlled trials". American Journal of Clinical Nutrition 2012;96(6):1281 to 1298. Abstract. doi.org/10.3945/ajcn.112.044321. Accessed 28 October 2026.
5. Murphy C, Koehler K. "Energy deficiency impairs resistance training gains in lean mass but not strength: a meta-analysis and meta-regression". Scandinavian Journal of Medicine and Science in Sports 2022;32(1):125 to 137. Full text. doi.org/10.1111/sms.14075. Accessed 28 October 2026.
6. Longland TM, Oikawa SY, Mitchell CJ, Devries MC, Phillips SM. "Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial". American Journal of Clinical Nutrition 2016;103(3):738 to 746. Full text. Funded by the Natural Sciences and Engineering Research Council of Canada; the senior author declares funding and honoraria from dairy bodies. doi.org/10.3945/ajcn.115.119339. Accessed 28 October 2026.
7. Weinheimer EM, Sands LP, Campbell WW. "A systematic review of the separate and combined effects of energy restriction and exercise on fat-free mass in middle-aged and older adults: implications for sarcopenic obesity". Nutrition Reviews 2010;68(7):375 to 388. Abstract. doi.org/10.1111/j.1753-4887.2010.00298.x. Accessed 28 October 2026.
8. Scientific Advisory Committee on Nutrition (SACN), "Statement on nutrition and older adults living in the community", 20 January 2021, paragraphs 3.2 and 4.22 to 4.24. gov.uk/government/publications/sacn-statement-on-nutrition-and-older-adults. Accessed 28 October 2026.
9. Morton RW and colleagues. "A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults". British Journal of Sports Medicine 2018;52(6):376 to 384. Full text. The senior author declares support from the US National Dairy Council, which funded some of the trials analysed. pmc.ncbi.nlm.nih.gov/articles/PMC5867436. Accessed 28 October 2026.
10. NHS, "Physical activity guidelines for adults aged 19 to 64", page last reviewed 22 May 2024. nhs.uk/live-well/exercise/physical-activity-guidelines-for-adults-aged-19-to-64. Accessed 28 October 2026.
11. Garthe I, Raastad T, Refsnes PE, Koivisto A, Sundgot-Borgen J. "Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes". International Journal of Sport Nutrition and Exercise Metabolism 2011;21(2):97 to 104. Abstract. doi.org/10.1123/ijsnem.21.2.97. Accessed 28 October 2026.
12. Ashtary-Larky D and colleagues. "Rapid weight loss vs. slow weight loss: which is more effective on body composition and metabolic risk factors?". International Journal of Endocrinology and Metabolism 2017;15(3):e13249. Full text. pmc.ncbi.nlm.nih.gov/articles/PMC5702468. Accessed 28 October 2026.
13. NHS, "Overweight and obesity in adults", page last reviewed 29 April 2026. nhs.uk/conditions/overweight-and-obesity. Accessed 28 October 2026.
14. Mamerow MM and colleagues. "Dietary protein distribution positively influences 24-h muscle protein synthesis in healthy adults". Journal of Nutrition 2014;144(6):876 to 880. Full text. Supported in part by the Beef Checkoff. pmc.ncbi.nlm.nih.gov/articles/PMC4018950. Accessed 28 October 2026.
15. Public Health England, "Government Dietary Recommendations: energy and nutrients for males and females aged 1 to 18 years and 19+ years", 2016, Table 2 (page 7) and footnotes. assets.publishing.service.gov.uk, government_dietary_recommendations.pdf. Accessed 28 October 2026.

Numbered markers in the page text link to these entries. Statistics describe populations, not any one person’s results.

Published 3 November 2026.