Can You Lose Fat and Build Muscle at the Same Time? What the Evidence Says

Losing fat and building muscle are two of the most common goals people bring to the gym, but they pull in slightly different directions. Doing both at once, often called body recomposition, is possible if you get the basics right. Here's what the evidence says.

Why is it hard to lose fat and build muscle at the same time?

It comes down to energy balance. To lose fat, you need to use more energy (kilojoules) than you eat. Building muscle works best with enough energy coming in. In the short term, an energy deficit lowers anabolic hormones and slows muscle protein synthesis, the process your body uses to build new muscle.¹

A meta-analysis of resistance training trials found that people training in an energy deficit gained less lean mass than people who weren't dieting, although their strength gains were similar. A deficit of about 2,100 kJ (500 Calories) a day was enough to stop lean mass gains altogether.¹

Who can lose fat and build muscle at the same time?

Recomposition tends to be easier if you're:

• new to resistance training;
• getting back into training after a long break;
• carrying more body fat to start with.

If you've been training consistently for years and are already lean, progress will be slower, and you may get better results by focusing on one goal at a time.

How big should your energy deficit be?

Keep it small. Because a deficit of around 2,100 kJ (500 Calories) a day can stop lean mass gains,¹ aim for a smaller deficit if building muscle is a priority. Fat loss will be slower, but you'll give yourself a better chance of gaining or keeping muscle along the way.

How much protein do you need to build muscle while losing fat?

A meta-analysis of 49 trials found that protein helped resistance training build muscle size and strength, but total intakes above about 1.6 g per kilogram of body weight a day gave no extra gains in lean mass.² For a 75 kg person, that's about 120 g a day.

Spread your protein across meals and snacks. Good sources include lean meat, chicken, fish, eggs, dairy, tofu, legumes and nuts.

What's the best training to lose fat and build muscle?

Resistance training is the priority. Australian guidelines recommend muscle-strengthening activities on at least 2 days a week.⁶ Compound exercises like squats, deadlifts, presses and rows work several large muscle groups at once.

You don't have to lift very heavy to build muscle. A meta-analysis found muscle growth was similar with light and heavy loads when sets were taken close to failure. Heavy loads were better for building maximal strength.³ If you're new to lifting, build up gradually with a qualified coach or exercise professional. Check in with your practitioner first if you're new to exercise or managing a health condition.

To keep making progress, gradually increase the challenge over time, for example by adding weight, reps or sets.

Does sleep affect fat loss and muscle?

Yes. In a controlled trial, adults on a reduced-kilojoule diet who slept 5.5 hours a night lost 55% less fat and 60% more lean mass than when they slept 8.5 hours.⁵ The study was small and short, but it suggests sleep matters for keeping muscle while you diet.

Sleep and rest days also give your muscles time to repair, which lowers your risk of injury and burnout.

Practical tips for body recomposition

• Build a routine: make training part of your week, not something you squeeze in.
• Plan your meals: having protein-rich meals and snacks ready makes it easier to hit your targets when life is busy.
• Track your progress: a training log helps you see when to increase the challenge.
• Warm up and cool down: this helps you move well and prepares your body for the session.
• Be patient: recomposition is slow, so judge progress over months, not weeks.

Frequently asked questions

Can you lose fat and build muscle at the same time?

Yes, especially if you're new to training, returning after a break or carrying more body fat. It works best with a small energy deficit, enough protein and regular resistance training.

How big a calorie deficit can you have and still build muscle?

Research suggests a deficit of about 2,100 kJ (500 Calories) a day can stop lean mass gains, so keep your deficit smaller than that.

How much protein do I need for body recomposition?

Around 1.6 g per kilogram of body weight a day. Eating more than that hasn't been shown to add extra lean mass.

Do I need to lift heavy weights to build muscle?

No. Light and heavy loads build similar muscle when sets are taken close to failure, though heavy loads build more maximal strength.

Is HIIT better for fat loss than steady cardio?

Fat loss is similar with both. HIIT just takes less time.

Does sleep affect body composition?

Yes. Short sleep during a diet has been linked with losing less fat and more lean mass.

References

Research (PubMed)

1. 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. PubMed 34623696
2. Morton RW, Murphy KT, McKellar SR, et al. 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. Br J Sports Med. 2018;52(6):376–384. PubMed 28698222
3. Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW. Strength and hypertrophy adaptations between low- vs. high-load resistance training: a systematic review and meta-analysis. J Strength Cond Res. 2017;31(12):3508–3523. PubMed 28834797
4. Wewege M, van den Berg R, Ward RE, Keech A. The effects of high-intensity interval training vs. moderate-intensity continuous training on body composition in overweight and obese adults: a systematic review and meta-analysis. Obes Rev. 2017;18(6):635–646. PubMed 28401638
5. Nedeltcheva AV, Kilkus JM, Imperial J, Schoeller DA, Penev PD. Insufficient sleep undermines dietary efforts to reduce adiposity. Ann Intern Med. 2010;153(7):435–441. PubMed 20921542

Australian guidelines

6. Australian Government Department of Health. Physical activity and exercise guidelines: recommendations for adults (18 to 64 years). View source

This article is general information and isn't a substitute for personalised advice. Speak to your practitioner about your situation.