For years you heard it: you either gain muscle or you lose fat, and both at once is impossible. The data from 2026 say something different.
Short answer: For most people who train in a gym, it is possible. It does not work for everyone, and not at the same speed. In the Vargas-Molina 2026 study (30 resistance-trained adults, 10 weeks, measured with a DXA scan), the group eating 250 kcal (calories) below maintenance lost 2.94 kg of fat and gained 1.04 kg of lean mass.
What the study found
Thirty resistance-trained adults, mostly young men, trained four days a week for 10 weeks. Body composition was measured with DXA, a body scan. Two groups got a food plan with high protein (2.5 g per kg of body weight). The third group trained the same way but ate as usual.
- Deficit group (250 kcal below maintenance): -2.94 kg of fat, +1.04 kg of lean mass.
- Maintenance group: -1.41 kg of fat, +0.97 kg of lean mass.
- Control group (same training, no supervision of food): no change.
Lean mass on a DXA scan is mostly muscle, but it is not a direct muscle measurement. This was also a small study, 10 people per group. Treat it as an early signal and no more than that.
The energy maths still holds
This does not break thermodynamics. Every kilogram of body fat holds roughly 7,700 kcal. In a mild deficit your body takes its energy from there. When it also gets a strength stimulus and enough protein, it can use some of that energy to build muscle. No miracle, just physiology.
Do not steer by the scale
Do not expect the number on the scale to go down in a straight line. Glycogen, water and salt move it by a kilo or two from day to day (more in why your weight fluctuates). When you recomp, which means you lose fat and gain muscle at the same time, track measurements, photos and your performance in the gym.
The conditions
To be fair, it works only under a few conditions:
- Strength training with progressive overload, about 3 to 5 times a week.
- Protein 1.6-2.2 g/kg. The upper end works more as insurance than as extra building material.
- A mild deficit of about 10 to 20%, not an aggressive one.
- Sleep of at least seven hours (see sleep and fat loss).
Who gets it fastest
Beginners, people who come back after a break, and people with a higher body fat percentage. An advanced lifter close to their ceiling will mostly do better with the classic cycles of gaining and cutting.
Frequently asked questions
What are the conditions for this to work?
Only a few: strength training with progressive overload about 3 to 5 times a week, protein 1.6-2.2 g/kg, a mild deficit of about 10 to 20%, and sleep of at least seven hours. The upper end of the protein range works more as insurance than as extra building material.
Who builds muscle fastest in a deficit?
Beginners, people who come back after a break, and people with a higher body fat percentage. An advanced lifter close to their ceiling will mostly do better with the classic cycles of gaining and cutting.
How can the body build muscle when energy is short?
Every kilogram of body fat holds roughly 7,700 kcal, and in a mild deficit your body takes energy from there. When it also gets a strength stimulus and enough protein, it uses some of that energy to build muscle.
How do I know a recomposition is working?
Do not go by the number on the scale, because glycogen, water and salt move it by a kilo or two from day to day. Track measurements, photos and your performance in the gym.
How did the other groups in the study do?
The maintenance group lost 1.41 kg of fat and gained 0.97 kg of lean mass. The control group, with the same training but no supervision of food, stayed unchanged.
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Apply for coaching Get the free Fat Loss KitSources, so you can check:
1) Vargas-Molina S, et al. Comparison of two nutritional protocols in body re-composition of resistance-trained participants. Eur J Appl Physiol. 2026;126(7):4019-4030. DOI: 10.1007/s00421-026-06209-6 | PMID: 41940947
2) Slater GJ, et al. Is an energy surplus required to maximize skeletal muscle hypertrophy associated with resistance training. Front Nutr. 2019;6:131. DOI: 10.3389/fnut.2019.00131 | PMID: 31482093
3) Longland TM, et al. 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. Am J Clin Nutr. 2016;103(3):738-746. DOI: 10.3945/ajcn.115.119339 | PMID: 26817506
4) Murphy C, Koehler K. Energy deficiency impairs resistance training gains in lean mass but not strength: a meta-analysis and meta-regression. Scand J Med Sci Sports. 2022;32(1):125-137. DOI: 10.1111/sms.14075 | PMID: 34623696
Martin Barna
Online nutrition and fitness coach. Since 2013 I have helped 600+ people lose fat and keep the result. Science, not crash diets.
Apply for coachingThis article is for information only. It is not medical advice. If you have a health condition, talk to your doctor.