You have a belly that won't shift, less interest in sex than before, and your energy isn't what it used to be. Three complaints you would probably mention separately to your GP. Yet in men they can tell one underlying story.
In men, belly fat, low testosterone and insulin resistance often go together. They can reinforce each other: belly fat can lower testosterone, and low testosterone can encourage fat storage around your waist. This is one of the most underrated connections in men's health, because it is rarely discussed in one breath while it is often one circle.
How are belly fat and testosterone connected?
Fat tissue around your belly is hormonally active and can convert testosterone into oestrogen via the enzyme aromatase. As a result, more belly fat can go together with lower testosterone. The other way round, low testosterone can make it harder to keep muscle mass and lose fat. This can create a loop that sustains itself.
Where does insulin come in?
Belly fat also relates to insulin resistance, where your body responds less well to insulin. HbA1c and HOMA-IR can say something about that. The Diabetes Fonds describes belly fat as one of the factors associated with an increased risk of type 2 diabetes. See also recognising insulin resistance.
The circle in view
The table below shows how the three can influence each other. These are associations, not laws: not everyone with belly fat has low testosterone, and vice versa.
| Link | What can happen | Which blood value can show something |
|---|---|---|
| Belly fat rises | More conversion of testosterone to oestrogen | Testosterone, oestradiol |
| Testosterone drops | Harder to keep muscle mass, fat accumulates | Testosterone, SHBG |
| Insulin works less well | Blood sugar can gradually become dysregulated | HbA1c, HOMA-IR |
Not all belly fat is the same
There is a difference between the fat just under your skin that you can grab, and the deeper fat around your organs, known as visceral fat. It is that deeper belly fat that is hormonally most active and relates most strongly to insulin resistance and an unfavourable testosterone. That is why a man with a relatively slim appearance but a lot of visceral fat can still have an unfavourable metabolic profile, a pattern sometimes called "skinny fat". Your waist circumference often says more than your weight on the scale. The Hartstichting therefore uses waist size as a practical measure of metabolic risk.
Why this plays out extra in men
Men store fat around the belly sooner than women, who naturally store more on hips and thighs. That makes men more sensitive to exactly the type of fat that is metabolically most active. Add to that the fact that testosterone gradually declines with age, and you see why the circle of belly fat, low testosterone and insulin resistance recurs so often in middle-aged men. It is not an inevitable fate, but it is something to take seriously.
What can you do with it?
The circle can often be broken, and knowing where you stand helps. Both the Voedingscentrum and the Hartstichting point to strength and endurance training, fibre-rich food and enough sleep as ways that can favourably influence your metabolic health. Strength training is extra interesting here: more muscle mass can improve your insulin sensitivity and make your body composition more favourable. Losing belly fat often improves your insulin sensitivity and your testosterone at the same time, because they hang on the same loop. The Diabetes Fonds stresses that even a modest reduction in belly fat can favourably influence your metabolic values. Always discuss low testosterone or dysregulated blood sugar with your GP, because what fits remains bespoke.
My take: chasing testosterone in a jar while ignoring your belly fat and blood sugar is mopping with the tap running. The gain often lies precisely on the lifestyle side of the circle. Tackle the cause and your testosterone, your insulin sensitivity and your cardiovascular profile often all benefit at once, because they hang on the same dials.
Getting started
The Metabolic Health Check looks at your blood sugar, and the Testosterone Panel at your testosterone, so you see both sides. At Caliberhealth, BIG-registered doctors assess the connection, not just the separate numbers. See also the pillar cholesterol in men.
Frequently asked questions
Does belly fat really lower my testosterone?
Belly fat can relate to lower testosterone, partly because fat tissue can convert testosterone into oestrogen. It is an association, not a law that applies to everyone. Discuss your values with your GP.
Will my testosterone rise if I lose weight?
In some men, losing weight, especially belly fat, can go together with a more favourable testosterone. How much varies per person, and what fits you is something you decide together with a doctor.
Which measure says more: weight or waist size?
For metabolic risk, your waist size often says more than your weight alone, because it is the deeper belly fat that is hormonally active.
This article provides general information and is not a substitute for medical advice. A blood test is a tool, not a diagnosis in itself. With serious symptoms, contact your GP, or call emergency services in an emergency.
Author
Caliberhealth
Dr. Naimi, BIG-registered physician, oversees the medical standards behind our content and assessments. Read our medical policy
