The importance of muscle mass in obesity

Guest writer: Rob van Berkel, Research dietitian and writer on nutrition and health

The importance of muscle mass in obesity

When obesity is discussed, people usually think of a high BMI — in other words, a high body weight relative to body height. Muscle mass often remains overlooked, even though having sufficient muscle mass in obesity is important for health. And not infrequently we see (or actually don’t see) that it is on the low side in obesity.

What is obesity?

The World Health Organization (WHO) defines obesity as:
“An abnormal or excessive fat accumulation that presents a risk to health.”

Since the 1980s, the Body Mass Index (BMI) has been used to determine obesity. BMI is calculated by dividing body weight (in kg) by height (in meters) squared.

A value between 18.5 and 25 is considered healthy.
Between 25 and 30 is classified as overweight, and above that as obesity.

To indicate the severity of obesity, three classes are distinguished:

  • Class I: 30–35

  • Class II: 35–40

  • Class III: > 40 kg/m²

In 2022, more than 2.5 billion adults worldwide were overweight (BMI > 25.0 kg/m²), of whom 890 million had obesity (WHO, 2025). Obesity in particular is associated with numerous negative consequences, including:

Physical consequences

  • Cardiovascular diseases

  • Type 2 diabetes

  • Various types of cancer

  • Sleep apnea

  • Joint problems

  • Fatty liver disease

  • Fertility problems

Psychological and social consequences

  • Depression and anxiety

  • Stigma and discrimination

  • Reduced quality of life

Economic consequences

  • High healthcare costs

  • Lower productivity

BMI says little about health

Although BMI can say something about health at the population level, it says little at the individual level (Barber et al., 2025). This is because BMI only considers body weight and not body composition, while body composition actually influences health. BMI says nothing about the amount of fat mass and muscle mass.

For example, a person who is 1.70 meters tall and weighs 100 kg has a BMI of 34.6 kg/m². That person could have:

  • 40 kg fat mass (40%) and 20 kg muscle mass,
    but also

  • 10 kg fat mass (10%) and 50 kg muscle mass.

Additionally, we know that particularly visceral fat in the abdominal cavity — not fat on the hips — is harmful to health (Neeland et al., 2017). BMI says nothing about this, especially at the individual level.

This has long been known, which is why it is now recommended to measure waist circumference in addition to BMI, as this is an indicator of abdominal fat (Ross et al., 2020; Khawaja et al., 2024).

The importance of sufficient muscle mass

Fat in the abdominal cavity increases the risk of clinical obesity, but having sufficient muscle mass lowers this risk.

Muscles not only allow you to stand, move, and breathe, they also:

  • influence basal metabolism

  • produce heat

  • secrete signaling substances (myokines)

  • regulate the metabolism of glucose, amino acids, and fatty acids

Research shows that muscles are responsible for more than 80% of glucose uptake after a glucose load (Merz et al., 2020).

The relationship between obesity and muscle mass

For a long time, little attention was paid to muscle mass in obesity. This is because, unlike BMI, it is not easy to measure and BMI is used by everyone. This is slowly changing, as several studies show that some obesity medications can lead to excessive loss of fat-free mass (including muscle mass) (Neeland et al., 2024).

On average, people with obesity have greater muscle mass than people without obesity (Cava et al., 2017). This can be explained by the heavier body weight they have to carry daily. Nevertheless, low muscle mass also occurs in people with obesity (Barrazoni et al., 2020).

When obesity thresholds are exceeded while muscle mass and muscle strength fall below certain cut-off values, this is referred to as sarcopenic obesity (Donini et al., 2022).

Prevalence:

  • 11% in older adults (Gao et al., 2021)

  • 27% in people with diabetes (Zhou et al., 2023)

In addition, muscle quality is often lower due to fatty infiltration (Cava et al., 2017). Natural aging contributes to this, but obesity itself and obesity-related health problems such as insulin resistance and chronic low-grade inflammation also play a role. In obesity, fatty acids and pro-inflammatory cytokines can escape from fat cells and infiltrate muscle cells (Axelrod et al., 2023). This attracts immune cells to the muscle, which can lead to loss of muscle mass and function and chronic low-grade inflammation. These inflammatory processes can also spread via the bloodstream to other organs and impair their function. Having both obesity and low muscle mass therefore represents a double burden (Barrazoni et al., 2020).

Gaining insight into muscle mass in obesity

Research often measures fat mass and fat-free mass. Fat-free mass consists of:

  • muscle mass

  • bones

  • organs

  • body water (intra- and extracellular)

Roughly 45–50% of fat-free mass consists of muscle mass (Oliver et al., 2025). The gold standards for measuring fat-free mass/muscle mass in obesity are DEXA and MRI. However, these methods are costly, time-consuming, and not always available.

Using BIA (Bioelectrical Impedance Analysis) is therefore an option. In a joint position statement by ESPEN and EASO, DEXA is recommended as the first choice for assessing muscle mass in the diagnosis of sarcopenic obesity (Donini et al., 2022). BIA is mentioned as the best alternative when corrected for body weight. BIA is suitable for estimating fat-free mass/muscle mass at the group level in overweight and obesity (Becroft et al., 2019).

However, although there is no better alternative, it should be considered that at the individual level — especially in obesity — BIA is less accurate. Most studies show that BIA overestimates fat-free mass compared to DEXA, with an asymmetric margin of error (95% limits of agreement) of about 5–10%.

Multifrequency and segmental BIA and devices using specialized (proprietary) obesity algorithms are preferred, but still overestimate fat-free mass and therefore muscle mass at the individual level.

How can you preserve muscle mass during weight loss?

Weight loss occurs when energy intake is lower than energy expenditure.

On average:

  • 75% of weight loss = fat mass

  • 25% = fat-free mass

With obesity medication, the loss of fat-free mass may be twice as high. The most important strategies to limit muscle loss are:

  • Consume sufficient protein (1.0–1.5 g/kg/day)

  • Engage in physical activity, preferably strength training

Conclusion

Muscle mass plays an essential role in healthy metabolism and overall health. Although people with obesity generally have more muscle mass, low muscle mass and reduced muscle quality frequently occur and may increase health risks.

Monitoring muscle mass is therefore important, but accurately assessing it at the individual level remains challenging.

References

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