More muscle, less fat: the metabolism booster

The statement “Muscles make you slim” sounds at first like a slogan from the world of fitness. However, there is a well-established scientific basis behind this claim. Muscle tissue plays a central role in the body’s energy metabolism, influences basal metabolic rate and contributes to long-term weight regulation. In this report, we examine how muscle mass increases calorie expenditure, the physiological processes involved, and why building muscle is important not only for aesthetic reasons but also for health.

Muscle tissue is metabolically active, which means that it requires energy to maintain its function. Even at rest, muscles burn calories – more than any other tissue apart from organs such as the liver or brain. Studies show that, per kilogram of muscle mass, around 13–15 kcal are consumed per day at rest. By way of comparison, one kilogram of fat tissue consumes just 4–6 kcal per day....

Muscle work and energy expenditure

During physical activity, the energy expenditure of the muscles increases enormously. In particular, high-intensity training sessions such as strength training or HIIT (High-Intensity Interval Training) lead to what is known as the ‘afterburn effect’ (EPOC – Excess Post-Exercise Oxygen Consumption). This effect ensures that the body continues to burn more calories for hours after the workout.

Basal metabolic rate refers to the amount of energy the body requires at rest to maintain basic functions such as breathing, heartbeat and cell regeneration. Muscle mass has a direct influence on the basal metabolic rate, as more muscle tissue leads to a higher energy requirement.

The effect of age

As we age, the body loses muscle mass (‘sarcopenia’), which reduces the basal metabolic rate. This explains why many people find it easier to put on weight as they get older. Regular strength training can slow down this loss and help maintain a stable basal metabolic rate.

The development and maintenance of muscle mass depend heavily on hormonal factors:

• • Testosterone: Promotes muscle growth and boosts the metabolism.
• • Growth hormone (HGH): Supports tissue regeneration and growth.
• • Insulin: Regulates the uptake of nutrients by the muscles, particularly amino acids.
• • Myokines: These signalling substances released by muscles have anti-inflammatory effects and positively influence overall metabolism.

A common misconception is that muscles ‘burn’ fat directly. In fact, muscles support fat loss indirectly by increasing the body’s overall calorie expenditure. Regular exercise and strength training increase the muscles’ sensitivity to insulin, which in turn reduces fat storage.

• • Strength training: Builds muscle mass and increases your basal metabolic rate.
• • Endurance training: Improves fat burning during exercise
• • Combined training: Maximises energy expenditure and improves body composition.

• 1. Weight management: Easier fat loss and sustainable weight control.
• 2. Improved insulin sensitivity: Protection against type 2 diabetes.
• 3. Increased bone density: Prevention of osteoporosis.
• 4. Improved cardiovascular health: Through the release of myokines.

Wilmore et al. (2001): Showed that strength training can increase basal metabolic rate by up to 7 per cent.

Bouchard et al. (2015): Found that people with greater muscle mass have a lower risk of metabolic diseases.

Hunter et al. (2000): Confirmed the effect of strength training on fat burning, particularly in post-menopausal women.