Why Perimenopause Can Affect Metabolism & Weight Changes

Understanding the Hormonal Changes Behind Body Composition During Midlife

Have you noticed that during your 40s or early 50s your body seems to change, even though your eating habits and exercise routine haven't?

Perhaps you're gaining weight around your waist, finding it harder to build or maintain muscle, experiencing stronger food cravings, or simply feeling like your metabolism has slowed.

You're not imagining it.

Perimenopause is much more than changes to your menstrual cycle. It is a period of significant hormonal and metabolic change that affects almost every system in the body—including your muscles, fat tissue, liver, brain, gut microbiome and energy production.

Understanding these changes can help you make informed nutrition and lifestyle choices to support your overall health.

Why do hormones influence metabolism during perimenopause?

During your reproductive years, estrogen plays an important role in supporting healthy metabolism.

As estrogen levels begin to fluctuate and gradually decline during perimenopause, several physiological changes may occur simultaneously.

These changes may influence:

• Muscle mass

• Insulin sensitivity

• Body fat distribution

• Appetite regulation

• Energy production

• Inflammation

• Liver health

Rather than one single cause, weight changes during perimenopause are usually the result of many interconnected processes.

Estrogen helps maintain muscle mass

One of estrogen's lesser-known roles is helping maintain healthy muscle.

Estrogen has an anabolic (muscle-preserving) effect. Throughout the reproductive years it helps support muscle maintenance, repair and recovery.

Why is muscle so important?

Muscle is one of the body's largest metabolically active tissues.

Healthy muscle helps:

• Support insulin sensitivity

• Regulate blood glucose

• Increase daily energy expenditure

• Support healthy mitochondrial function

• Promote healthy ageing

• Maintain strength and mobility

As estrogen declines during perimenopause, women naturally become more catabolic, meaning muscle protein breakdown gradually exceeds muscle building if no intervention occurs.

This gradual loss of muscle, known as sarcopenia, is one reason metabolism may slow during midlife.

For this reason, adequate protein intake and regular resistance training become increasingly important during perimenopause.

The role of follicle-stimulating hormone (FSH)

As estrogen declines, the brain produces increasing amounts of follicle-stimulating hormone (FSH).

FSH is traditionally recognised for its role in regulating ovarian function. However, emerging research suggests that FSH receptors are also present in several tissues throughout the body, including adipose (fat) tissue.

Researchers are currently investigating how rising FSH levels may contribute to changes in body composition during menopause.

Some studies suggest that higher FSH levels may be associated with:

• Enlargement of existing fat cells (adipocyte hypertrophy)

• Increased fat storage

• Increased lipogenesis (formation of new fat)

• Greater abdominal fat accumulation

Although research is continuing in this area, these findings may help explain why many women notice increasing abdominal fat despite maintaining similar eating habits.

Muscle loss affects insulin sensitivity

Muscle plays a major role in blood glucose regulation.

When muscle mass declines:

• Less glucose is taken up from the bloodstream.

• Insulin sensitivity may decrease.

• Blood glucose regulation becomes less efficient.

Maintaining muscle through resistance exercise and adequate dietary protein is one of the most effective lifestyle strategies for supporting healthy glucose metabolism during midlife.

Changes in leptin and appetite regulation

Leptin is often referred to as the "satiety hormone."

It helps signal to the brain that the body has stored enough energy.

As abdominal fat increases, leptin levels also tend to increase. However, in some individuals the brain becomes less responsive to leptin's signals—a process often referred to as reduced leptin sensitivity.

This may contribute to:

• Increased appetite

• Reduced satiety

• Stronger food cravings

• Increased energy intake

Appetite regulation during perimenopause is influenced by many factors, including sleep, stress, hormones and body composition.

Mitochondria and energy production

Mitochondria are often called the powerhouses of our cells because they produce the energy needed for virtually every function in the body.

Ageing, declining estrogen, reduced physical activity and chronic inflammation may all influence mitochondrial function.

When mitochondrial function becomes less efficient, some women may notice:

• Lower energy levels

• Reduced exercise tolerance

• Slower recovery

• Changes in metabolic flexibility

Regular physical activity—particularly resistance training—alongside a nutrient-rich eating pattern may help support healthy mitochondrial function.

Stress adds another layer

Perimenopause often coincides with one of the busiest stages of life.

Many women are balancing careers, caring responsibilities, ageing parents, teenagers, financial pressures and disrupted sleep.

Chronic stress activates the release of cortisol, a hormone involved in the body's stress response.

Persistently elevated cortisol may influence:

• Appetite

• Blood glucose regulation

• Food cravings

• Sleep quality

• Fat distribution

For many women, stress management becomes just as important as nutrition.

Why abdominal fat matters

Abdominal (visceral) fat is different from the fat stored just beneath the skin.

Visceral fat surrounds the internal organs and is biologically active.

It produces signalling molecules known as pro-inflammatory cytokines, including TNF-α and IL-6.

These inflammatory compounds may contribute to chronic low-grade inflammation, which has been associated with metabolic dysfunction.

Visceral fat also drains directly into the portal vein, transporting free fatty acids and inflammatory molecules to the liver.

Over time, this may contribute to:

• Reduced insulin sensitivity

• Changes in lipid metabolism

• Increased fat accumulation within the liver

When excessive fat accumulates in the liver in people who drink little or no alcohol, it is known as metabolic dysfunction-associated steatotic liver disease (MASLD) (previously known as non-alcoholic fatty liver disease or NAFLD).

MASLD is increasingly recognised as one of several metabolic conditions associated with insulin resistance.

Supporting your metabolism during perimenopause

Although hormonal changes cannot be stopped, there are many evidence-informed lifestyle strategies that may support metabolic health during this stage of life.

These include:

Prioritise protein

Aim to include a quality source of protein at each meal to support muscle maintenance and satiety.

Build muscle

Resistance training helps maintain muscle mass, supports healthy ageing and contributes to healthy glucose metabolism.

Eat plenty of fibre

A diet rich in vegetables, legumes, whole grains, nuts and seeds helps support digestive health and a diverse gut microbiome.

Support your gut microbiome

Emerging research suggests the gut microbiome may influence metabolic health through immune function, inflammation and the production of beneficial compounds such as short-chain fatty acids.

Prioritise sleep

Quality sleep supports appetite regulation, energy levels and overall wellbeing.

Manage stress

Stress management strategies such as walking, mindfulness, yoga and spending time outdoors may support overall health.

Stay active

Regular movement throughout the day, in addition to structured exercise, contributes to long-term metabolic health.

Clinical takeaway

Perimenopause is not simply about changing hormones.

It is a complex interaction between:

• Declining estrogen

• Rising FSH

• Loss of muscle mass

• Changes in insulin sensitivity

• Appetite regulation

• Mitochondrial function

• Stress hormones

• Inflammation

• Gut microbiome health

• Liver metabolism

Understanding these interconnected systems helps explain why supporting metabolic health during perimenopause requires a whole-person approach rather than focusing on calories alone.

Rather than searching for one "magic solution," consider building sustainable habits that support your health over time.

Small, consistent changes—including resistance training, adequate protein, a fibre-rich eating pattern, quality sleep and stress management—can make a meaningful difference to your overall wellbeing.

A clear infographic showing the cascade:

⬇️↓ Estrogen

⬇️↓ Muscle mass (less anabolic)

⬇️↓ Insulin sensitivity

⬇️↑ Blood glucose & insulin demand

⬇️↑ Visceral fat

⬇️↑ Inflammatory cytokines

⬇️↑ Liver fat (MASLD risk) & metabolic dysfunction

Alongside a second pathway:

↓ Estrogen → ↑ FSH → FSH receptors in fat tissue → larger fat cells + increased lipogenesis → abdominal fat accumulation

Want to learn more?

If you're interested in evidence-based nutrition information on gut health, thyroid health, hormones, perimenopause and the gut microbiome, I'd love to keep in touch.

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Disclaimer: This article is intended for general educational purposes only and does not replace personalised medical advice, diagnosis or treatment. Always consult your GP or qualified healthcare practitioner before making changes to your diet, exercise routine or supplements.