Changing ovarian hormone production across mid-life can influence where fat is stored in the body, but it doesn’t have to influence how much fat we store. Yet none of this is the whole biochemical story. Insulin sensitivity always matters but even more so at mid-life, as does muscle mass – and perhaps most fascinatingly, fat tissue itself as it is hormonally active. So rather than simply falsely believing that “perimenopause causes belly fat”, let’s look at what may actually be happening inside the body.

First, estrogen does far more than help regulate your cycle

We tend to associate estrogen with reproduction, yet its influence extends far beyond your ovaries and uterus. Estrogen receptors are found throughout the body and estrogen signalling is involved in numerous aspects of metabolic health, including glucose (sugar) and lipid (fat) metabolism, insulin sensitivity and the way fat is distributed. During the reproductive years, women tend to store proportionally more fat beneath the skin, particularly around the hips and thighs.

During mid-life, some women experience a shift towards storing more fat around the abdomen, including visceral fat around the internal organs. Importantly, this isn’t universal which means that not every (or even any) change in weight or body composition during your 40s and 50s is due to changes in ovarian hormone production. Ageing is happening at the same time and brings its own changes to muscle mass, energy expenditure and body composition. But the accumulation of too many poor quality lifestyle choices can become more visible at this time and these may have a particular relationship with where fat is stored.

Why does it matter where fat is stored?

Not all body fat behaves in the same way. Subcutaneous fat sits just beneath your skin. Visceral fat is stored deeper within the abdomen around your internal organs. This isn’t a conversation about how your stomach looks; it’s about what is happening metabolically. Visceral fat is biologically active and greater amounts are associated with reduced insulin sensitivity and an increased risk of metabolic diseases.

Which brings us to insulin. Insulin is a hormone produced by your pancreas. One of its key jobs is helping glucose move out of your bloodstream and into your cells, where it can be used for energy or stored for later in your muscles and liver. When your cells become less responsive to insulin, your pancreas needs to produce more of it to achieve the same effect. We call this insulin resistance, and this is where several parts of the picture begin to overlap.

Greater visceral adiposity, ****meaning a greater amount of fat stored deep inside the abdomen around the internal organs, is closely associated with poorer insulin sensitivity. This is partly because visceral fat is metabolically active and releases fatty acids and signalling molecules that can interfere with the way insulin works in the liver and muscles. As a result, the body usually needs to produce more insulin to help move glucose from the bloodstream into cells.

As estrogen declines, androgens (a group of hormones that men make more of than women; testosterone, for example is an androgen) can become relatively excessive (rather than sit within a healthy range) if someone is insulin resistant. This androgen excess in turn, makes the insulin resistance worse. It influences how responsive tissues are to insulin, how the body handles glucose after eating and where fat is preferentially stored. So as the hormonal environment changes, if there is also insulin resistance, body fat distribution can change and metabolic health can change alongside this. ****None of this ****means perimenopause automatically makes you insulin resistant. It means that if you’re noticing changes around your middle, it can be useful to look beyond the assumption that “this is just what happens at my age” and consider your metabolic health too.

Muscle is another important piece of the puzzle

Muscle tends to get discussed in terms of strength and appearance, but metabolically, it does an enormous amount of work. Skeletal muscle is one of the major places glucose goes when insulin signals for it to leave your bloodstream. Yet unless we are actively working to maintain muscle mass, it will decline over time, leaving less space for glucose to be stored there, which means more is left over for storage in fat cells.

This is one reason preserving and building muscle becomes increasingly important through midlife. It isn’t simply about changing your body composition. Maintaining muscle supports insulin sensitivity, glucose regulation, strength, mobility and bone health. So if your body is changing in your 40s or 50s, relentlessly trying to eat less is not the most useful response. Building and preserving metabolically active tissue deserves a major place in the conversation too.

And here’s where the biochemistry gets particularly interesting

We tend to think of body fat as stored energy. But adipose tissue is much more active than that. It is an endocrine tissue, meaning it produces and responds to chemical messengers and participates in your hormonal environment. One example is an enzyme called aromatase. Aromatase converts androgens into estrogens. It is present in several tissue types throughout the body, including adipose tissue.

Before menopause, your ovaries are the primary source of estradiol. As ovarian estrogen production declines (it does not cease, it decreases), estrogen continues to be produced in peripheral tissues and adipose tissue is one of sites where estrogens are produced from androgens. So consider what is happening here. Your changing ovarian hormones can influence your fat distribution. Your fat distribution is related to your metabolic health and insulin sensitivity. Your muscle influences glucose regulation and insulin sensitivity. And your adipose tissue itself participates in sex hormone metabolism. There isn’t one system operating in isolation.

Which is why “it’s just perimenopause” is inaccurate and unhelpful

Yes, it might be during the menopause transition when some women notice changes around their middle. But simply labelling that change as perimenopause misses an opportunity to understand what is contributing.

→ What is happening with your insulin sensitivity?

→ How much muscle are you carrying and what are you doing to preserve it?

→ How much are you moving throughout the day?

→ Are you getting enough sleep?

→ What does your way of eating look like?

→ How much alcohol are you consuming?

→ What is happening with your stress response?

→ And are there other health factors that need investigating?

These are not questions designed to make women feel responsible for every change that happens in their body. They are questions that give us somewhere useful to look. If your body begins changing in ways you don’t recognise, it can be tempting to think you’ve lost control of it. Or that this is simply what happens at this stage in life and there’s nothing you can do. Neither is particularly helpful. Your biochemical environment is changing and there may be several factors contributing to what you’re experiencing – understanding those factors gives you information. And information allows you to make choices that support your body through this stage rather than fighting against it.

Your body hasn’t stopped making sense. Sometimes we just need to look more closely at what it’s trying to tell us.