Metabolism in Your 40s: How to Support Your Body

As we cross the threshold into our 40s, many of us notice subtle changes in how our bodies manage energy. It can suddenly feel more challenging to maintain the weight, vitality, and muscle definition that once came so naturally. While it is common to blame a failing metabolism, the biological reality is far more nuanced, involving shifts in muscle mass, hormonal balance, and daily movement patterns.

How it works

Metabolism is the sum of every chemical reaction that keeps us alive, converting the nutrients we consume into the cellular energy our bodies need to function. The largest contributor to this is our basal metabolic rate (BMR), which represents the energy burnt simply keeping our organs functioning at rest. In our 40s, hormonal shifts—particularly declining oestrogen in women and gradual testosterone reductions in men—coincide with natural age-related muscle loss, historically referred to as sarcopenia.

Muscle tissue is highly metabolically active, meaning it burns more calories at rest than fat tissue. When we lose muscle, our resting metabolic rate naturally declines. However, high-profile clinical research suggests that total energy expenditure actually remains remarkably stable between the ages of 20 and 60, indicating that the metabolic "slowdown" we experience in our 40s is often less about an inevitable cellular decay and more closely linked to a gradual reduction in physical activity, muscle composition, and hormonal fluctuations.

Evidence-based benefits

• Preserving lean muscle through resistance training: Lifting weights or performing bodyweight exercises helps signal the body to rebuild muscle tissue, which may support a higher resting metabolic rate. Caveat: However, resistance training must be performed consistently and with proper form to avoid joint strain, and it may not fully offset hormonal metabolic shifts on its own.
• Prioritising dietary protein: Protein has a higher thermic effect of food (TEF) compared to carbohydrates or fats, meaning the body uses more energy to digest and process it, which may support metabolic efficiency. Caveat: Nevertheless, excessive protein intake can place undue strain on the kidneys in those with pre-existing conditions, so consumption should remain within recommended dietary guidelines.
• Increasing non-exercise activity thermogenesis (NEAT): Small daily movements, such as walking, standing, and taking the stairs, contribute significantly to daily energy expenditure and may support cardiovascular health. Caveat: While highly beneficial, increasing NEAT is a gradual lifestyle change and may not yield rapid weight management results without concurrent dietary adjustments.
• Optimising sleep duration and quality: Deep sleep plays a critical role in regulating hormones like ghrelin and leptin, which control appetite and metabolic signalling. Caveat: However, improving sleep hygiene may support metabolic balance, but it cannot compensate for a highly sedentary lifestyle or poor nutritional choices.
• Supporting metabolic health with adequate hydration: Drinking sufficient water temporarily increases the body's energy expenditure through water-induced thermogenesis and supports general cellular functions. Caveat: Even so, some evidence suggests this effect is relatively modest and short-lived, meaning hydration should be viewed as a foundational health habit rather than a primary tool for weight management.

How to take it / typical dose

When considering the lifestyle shifts required to support your metabolism in your 40s, consistency acts as your daily "dose". Clinical guidelines recommend aiming for a minimum of 150 minutes of moderate aerobic activity per week, alongside resistance training sessions at least 2 to 3 times weekly to actively stimulate muscle protein synthesis. Additionally, targeting a daily protein intake of approximately 1.2 to 2.0 grams per kilogram of body weight may support muscle preservation, though individual nutritional requirements will vary based on baseline health, weight, and general activity levels.

Safety and who should avoid it

Before making significant changes to physical activity or dietary intake in your 40s, it is important to consult a healthcare professional. Individuals with underlying joint issues, cardiovascular conditions, or chronic metabolic disorders like type 2 diabetes should seek medical clearance before commencing high-intensity strength training or restrictive dietary protocols. Rapidly increasing physical demands without proper progression can lead to acute injuries, while overly restrictive diets may lead to nutrient deficiencies and paradoxically slow down metabolic processes by triggering a starvation response.

The bottom line

While metabolic shifts in your 40s are a natural part of the ageing process, they are not entirely beyond your control. Focusing on muscle preservation, consistent daily movement, and balanced nutrition remains the most effective, clinically supported path to keeping your metabolic health vibrant for years to come.