Build muscle and lose fat at the same time?

Build muscle and lose fat at the same time

Having more muscle and less fat doesn’t just look aesthetic. It also has some health benefits and is associated with better performance. However, it is only possible to build muscle and lose fat at the same time to a very limited extent – or so it was thought until now.

At a glance

  • Actually, muscle building and fat loss are opposite processes. Muscle gain is anabolic, fat loss is catabolic.
  • Nevertheless, these processes can also take place at the same time. So far, this has been proven especially in the case of the untrained and the overweight.
  • But this phenomenon can also be observed in well-trained athletes. This is influenced by the type of training, diet and other factors.

Muscle gain or hypertrophy and fat loss are actually opposite processes. While an anabolic metabolic state is required for muscle building, a catabolic metabolic state is required for fat loss. A simultaneous occurrence of these opposing processes has so far only been observed in untrained and overweight individuals.

Anabolic is the term used to describe all those metabolic processes in which the body’s own substances such as fat and muscle are built up. Catabolic are all the processes in which the body’s own substances are broken down.

Combined strength and endurance training is particularly suitable for these simultaneous adjustments. Recent data show that this can be used to achieve simultaneous fat loss and muscle gain, even in people with training experience. Nutrition also plays a role in this. Often a high protein intake of> is recommended 2 g/kg/d. There are also reports that despite a positive calorie balance – i.e. an energy surplus – fat was lost. This was especially true if the excess was due to extra protein.

How to measure body composition?

When you look at the changes demonstrated in studies, you should also look at the methods used to measure them. Because these are based on different technologies and are not all equally accurate. It is also problematic that the changes in body composition often lie within the error range of the individual measurement methods. Common methods used to assess body composition include 4C, DEXA, air-displacement plethysmography (ADP), hydrodensitometry, and ultrasound.

Overview of body composition measurement methods

  • 4C: The name comes from the division of the body into 4 compartments. These are fat, water, minerals and protein. This is considered the gold standard. However, the measurement is very time-consuming and cost-intensive, since several independent investigations are necessary. Mineral content can be obtained by DEXA, body water by mass spectrometry from the deuterium oxide content of exhaled air, and body volume by weighing under water or by body plethysmography. From these three parameters together with the body mass, the individual compartments can be calculated.
  • DEXA (Dual energy x-ray absorptiometry): This is based on a 3C-model (3 compartments). With DEXA you can determine bone mass, fat mass and lean body mass. In addition, regional measurement is also possible, i.e. the body composition can be determined separately for all extremities. The standard error is about 1.6% compared to MRI. Changes in studies are often in this range. Therefore the comparability of successive studies is very good.
  • Air displacement plethysmography (ADP): Here, only fat mass and fat-free mass are measured, i.e. a 2-compartment model is used. In a closed chamber, the air displacement through the body is recorded, which allows conclusions to be drawn about the density and thus the distribution of fat and fat-free mass. Here, too, the results may differ by 1.8-3.6%, although the comparability of successive studies is again very good.
  • Hydrodensitometry: This measurement also targets the density of the body. After weight measurement on land, body weight is measured again under water. From this, including the volume of air remaining in the body, density can also be calculated.
  • Ultrasound: Ultrasound can be used to measure the thickness of the fat layer and also muscle volume. This method can work similarly well as DEXA for experienced examiners.

Training status influences adaptations

There are several factors that influence the changes induced by training. Whether one can build muscle and lose fat at the same time depends, among other things, on training experience. Significantly greater changes were measured in poorly trained study participants than in well-trained ones (FFM +5 kg, FM -1.4 kg vs. FFM +1.9, FM with no change, see Figure 1). At the beginning of the season, however, simultaneous muscle gain and fat loss can also be observed in well-trained athletes. For example, changes in both parameters were found in rugby players after a 4-week training break (FFM +1.8 kg, FM -2.2 kg).

Changes in fat-free mass and fat mass

In Physique athletes such as z.B. recomposition does not generally occur in bodybuilders. This is even more true for men than for female bodybuilders. Namely, in men, significantly reduced testosterone levels were found during energy deficit.

Which forms of training are the most effective if you want to build muscle and lose fat?

Studies on strength-trained athletes have shown that z.B. Circuit training with set breaks of 35 s in contrast to traditional strength training with 3 min set breaks leads to a statistically significant reduction of fat mass (1.5 vs. 1.1 kg). The muscle gain was comparable in both (1.5 vs. 1.2 kg). Another study showed that more fat can be lost if the same training volume is distributed over 2 instead of 4 training sessions per week (-2.4 vs. -0.6 kg), while muscle gain did not differ significantly (1.2 vs. 1.4 kg). In another study, this result could be compared with groups training 3x resp. 6x weekly training, not be reproduced. Here, only significant muscle gains but no fat loss were measurable.

Overall, it can be said that, in principle, the build-up of muscle mass and the loss of fat are possible at the same time, even in trained athletes.

Build muscle and lose fat with the right diet

Nutrition has a great impact on training performance, recovery and body composition when specifically combined with strength training. With a special diet, it is possible to achieve not only muscle building but also fat loss in the case of a positive energy balance. This is also possible in the case of an energy deficit. Here, lean body mass can increase while fat mass decreases. All in all, these processes do not seem to be explained by calorie deficits or surpluses alone. Several studies have shown that the simultaneous buildup of muscle mass and fat loss z.B. Is possible with very high protein or hypocaloric diets.

In one study, for example, subjects from two groups built up about the same amount of lean body mass (1.5 kg). Surprisingly, however, those with the higher protein intake of 3.4 g/kg (vs. 2.3 g/kg in the control group) shed more fat (-1.6 vs. -0.3 kg), although they ate about 500 kcal more per day. However, there were strong individual differences. For example, in both groups there were subjects who gained 7 kg of muscle mass and lost 4 kg of fat mass at the same time. The desired effect (building muscle and losing fat) was achieved in about 70% of the test subjects overall.

Other studies have also shown a recomposition effect, especially with a high protein intake. However, this was also the case in studies where diet had little influence (Rauch et al., 2018). There, people only supplemented with 25 g of Whey protein after training. However, the higher body fat percentage compared to the subjects in other studies may also have played a role here.

The right diet helps build muscle and lose fat

Overall, moderate to high protein in the diet along with progressive strength training can lead to recomposition effects. A higher body fat percentage at the beginning of the training program seems to favor these effects.

What influence do sleep and other factors have?

Another important component in simultaneous muscle building and fat loss is sleep. This is how overweight people lost the same amount of body mass regardless of the amount of sleep they had. But with only one hour of sleep deprivation 5 days a week, they lost proportionally significantly more muscle mass in the process. In this study, however, no strength training was performed. Interestingly, ghrelin levels were also elevated during sleep deprivation. Ghrelin is a hunger hormone.

Other studies have found poorer strength endurance and higher subjective effort in sleep-deprived individuals. Since training success is dependent on training volume, sleep deprivation can have a negative effect here as well. Thus, a strength training program could also lead to greater fat mass loss when combined with an intervention to improve sleep patterns. However, this was carried out on untrained subjects.


Simultaneous buildup of muscle mass and loss of fat mass seems to be possible even in trained athletes. However, there are various factors that influence the extent of the changes. This includes the training itself, the training condition and the body composition at the beginning of the training program. Nutrition and sleep may also play a role. If changes in body composition are desired, strength training should be performed at least three times a week, and should be intensified according to the progress of training. A protein intake of 2.6-3.5 g/kg improves the prospects for such adjustments and protein supplements can also help.

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