How to lose fat without losing muscle

Why you lose muscle when you lose weight

When you eat less than you burn, your body does not take the energy from fat alone. Part of the weight you lose is lean mass: muscle, water and other tissue. How much depends on what you do while you are in a deficit.

A review of 52 studies in middle-aged and older adults with overweight shows it clearly: among the groups that only dieted, 81% lost 15% or more of their weight as lean mass. Among those who dieted and exercised, only 39% did (Weinheimer et al., 2010). Diet alone takes weight off, but it takes more muscle with it.

You have four levers: how fast you lose, how much protein you eat, strength training and sleep.

How fast to lose weight

In a trial of athletes who lifted, the group that lost slowly (a target of 0.7% of body weight per week) gained 2.1% lean mass, while the group that aimed to lose twice as fast gained none (Garthe et al., 2011). That is why recommendations for people who train sit at 0.5% to 1% per week (Helms et al., 2014).

How much to lose per week and the rough daily deficit
Your weight	0.5% per week	1% per week
60 kg (132 lb)	0.3 kg (about 330 kcal a day)	0.6 kg (about 660 kcal a day)
70 kg (154 lb)	0.35 kg (about 390 kcal a day)	0.7 kg (about 770 kcal a day)
80 kg (176 lb)	0.4 kg (about 440 kcal a day)	0.8 kg (about 880 kcal a day)
90 kg (198 lb)	0.45 kg (about 500 kcal a day)	0.9 kg (about 990 kcal a day)

The math uses about 7,700 kcal per kilo, an approximation that falls short over time because your body burns a little less (Hall, 2008). If muscle is your priority, stay close to 0.5%: a meta-analysis found that a deficit of about 500 calories a day is already enough to stop lean mass gains in people who lift (Murphy and Koehler, 2022). To find your starting point, see how to work out your calorie deficit.

How much protein to eat in a deficit

During weight loss, the recommendation for athletes is 1.6 to 2.4 g of protein per kilo of body weight per day, toward the top the bigger the deficit and the harder the training (Hector and Phillips, 2018).

More protein, better body composition. In a 4-week trial with a large deficit and training 6 days a week, those who ate 2.4 g per kilo gained 1.2 kg of lean mass and lost 4.8 kg of fat. On 1.2 g per kilo they gained 0.1 kg of lean mass and lost 3.5 kg of fat (Longland et al., 2016).
If you are already lean, aim higher. Helms's review of lean athletes in a deficit suggests 2.3 to 3.1 g per kilo of lean mass, higher the leaner you are and the bigger the deficit (Helms et al., 2014).
Do the math with your weight. At 70 kg (154 lb), 1.6 to 2.4 g per kilo is 112 to 168 g a day. The protein calculator gives you your number and the protein per day guide explains how to spread it out.

How to train while you lose fat

Strength training is the signal that tells your body it still needs the muscle. In a meta-analysis of 114 trials in people with overweight, combining strength training with a diet took off 5.3 kg of fat and kept lean mass (Lopez et al., 2022).

Do not switch to light weights. Keep the same exercises and the challenging loads that built your muscle. If you can, try to keep or add weight with progressive overload.
Cardio is not the enemy. Adding cardio to strength training did not reduce muscle growth or maximal strength across 43 studies. It did slightly blunt explosive strength, mostly when both were done in the same session; keeping them at least 3 hours apart avoided that effect (Schumann et al., 2022).
Use a routine built for fat loss. See the fat loss routines if you want a ready-made plan.

Why short sleep makes you lose muscle

In one trial, 10 adults with overweight followed the same diet for 14 days twice: once sleeping 8.5 hours and once 5.5 hours. On short sleep they lost 0.6 kg of fat instead of 1.4 kg, and 2.4 kg of lean mass instead of 1.5 kg. They were also hungrier (Nedeltcheva et al., 2010).

It is a short, small study, but it points one way: the same deficit yields more fat and less muscle loss when you sleep enough.

Your plan in 4 steps

Work out your calories. Find your maintenance with the calorie calculator and take off a deficit that has you losing 0.5% to 1% per week.
Set your protein. 1.6 to 2.4 g per kilo of body weight per day, and split the rest of your calories with the macro calculator.
Lift. Keep your exercises and your loads. Cardio can go on top, ideally at another time of day.
Check in every two weeks. Look at your weekly average weight. If you lose faster than 1% per week, eat a little more; if you are not losing at all, cut 100 to 200 kcal.

Questions

Can you build muscle while losing fat?

Yes, especially if you are new to training or carry more body fat (Forbes, 2000). That is called body recomposition. With more experience and less fat, the usual outcome is keeping muscle, not gaining it.

How much protein do I need to keep my muscle?

1.6 to 2.4 g per kilo of body weight per day while you are in a deficit (Hector and Phillips, 2018). At 70 kg (154 lb) that is 112 to 168 g a day.

Does cardio make you lose muscle?

Not if you keep lifting. In a meta-analysis of 43 studies, adding cardio did not reduce muscle growth or maximal strength (Schumann et al., 2022).

How much weight can I lose per week without losing muscle?

0.5% to 1% of your body weight (Helms et al., 2014). In athletes, losing about 0.7% per week kept lean mass better than going twice as fast (Garthe et al., 2011).

Sources

This guide is for information only and does not replace advice from a health professional.