Stress, cortisol and how your body responds

Cortisol has become the villain of choice in wellness marketing. Blockers, detoxes, adrenal support protocols, "cortisol face". Almost none of it is grounded in anything.

Which is a shame, because chronic stress genuinely does affect body composition — just not through the mechanism being sold.

What cortisol actually is

A hormone released by the adrenal glands, following a daily rhythm: highest shortly after waking, declining through the day, lowest around midnight. It rises acutely in response to stress of any kind, including exercise.

Its job is to mobilise energy. It raises blood glucose, increases the availability of fatty acids, and dampens processes that are not immediately essential — including, over time, immune function and reproductive hormones.

That is a useful system. Cortisol is not a malfunction and it is not something to eliminate; people without adequate cortisol are seriously unwell.

Exercise raises cortisol. So does cold water, fasting, and every hard training session you have ever done. Acute elevation is normal and not a problem. The concern is chronic elevation, and that is a different thing.

What chronic stress actually does

Four mechanisms, three of which are behavioural.

1. It makes you eat more. The most important one by a distance. Stress reliably increases intake, and skews it toward calorie-dense, palatable food. This is well documented and it is where most of the weight effect comes from. Cortisol interacts with reward pathways, and "stress eating" is a real physiological phenomenon rather than a moral failing.

2. It wrecks your sleep. Elevated evening cortisol delays sleep onset and fragments sleep. Poor sleep then raises hunger and worsens training. The two compound.

3. It reduces your activity. Stressed, tired people move less, train less consistently, and skip sessions. NEAT falls.

4. It causes fluid retention. Cortisol has some mineralocorticoid activity, which promotes sodium and water retention. This produces genuine, visible puffiness — and it is the reason people under stress often look softer on the scale and in the mirror while their actual fat mass is unchanged.

That fourth point matters more than it seems. A great deal of "I'm stressed and gaining belly fat" is water, and it resolves within days of the stress lifting.

The "cortisol belly" claim

The specific claim is that cortisol causes fat to be deposited preferentially around the abdomen.

There is something real underneath it. Visceral fat tissue has a higher density of glucocorticoid receptors than subcutaneous fat, and in genuine pathological cortisol excess — Cushing's syndrome — the pattern of central fat deposition with thin limbs is unmistakable and diagnostic.

But Cushing's involves cortisol levels far beyond anything produced by a demanding job. In people with normal adrenal function, the evidence that ordinary chronic stress meaningfully redistributes fat storage, independent of the extra calories eaten, is weak.

The honest summary: stress makes you eat more and sleep worse, and that is where the abdominal fat comes from. The direct redistribution effect, if it exists at normal cortisol levels, is small compared with the behavioural route.

What does not work

Cortisol blockers and "adrenal support" supplements. There is no good evidence they meaningfully lower chronic cortisol or improve body composition. "Adrenal fatigue" is not a recognised medical diagnosis — the systematic review evidence does not support it as a condition.

Avoiding exercise to keep cortisol down. Exercise raises cortisol acutely and lowers chronic stress substantially. The net effect is strongly positive.

Cutting calories harder because stress is causing weight gain. If the gain is water and stress-eating, a more aggressive deficit adds another stressor to a system already overloaded.

What does work

Sleep. The single largest lever, and it works in both directions — stress ruins sleep, and poor sleep raises stress reactivity. Fixing sleep breaks the loop.

Regular moderate exercise. Consistently reduces measures of chronic stress and improves mood. Not maximal training — moderate, regular activity. Walking counts.

Time outdoors, particularly in the morning. Anchors circadian rhythm, which regulates the cortisol curve itself.

Reducing the actual stressor, where possible. Unglamorous and usually the real answer. No breathing protocol compensates for a job that is genuinely destroying you.

Breathing practices and meditation. The evidence is modest but real for stress markers and perceived stress. Worth trying; not a substitute for sleep or for addressing the source.

Not compounding it. A very aggressive diet, a high-volume training programme and a stressful period in life is three stressors at once. Something has to give, and choosing which is better than letting your body choose.

When to seek help

Some symptom patterns are worth a doctor rather than a lifestyle adjustment.

Unexplained rapid central weight gain with purple stretch marks, easy bruising, muscle wasting in the limbs and high blood pressure can indicate genuine cortisol excess. It is rare, but it is a real diagnosis with real treatment.

Persistent low mood, anxiety that interferes with daily function, or exhaustion that does not respond to rest are also worth taking to a GP. Framing a mental health problem as a hormone optimisation problem delays the treatment that would actually help.

Training as a stressor you can dose

Exercise is a stressor, and that is precisely why it works — the adaptation is the response to it. But it draws on the same recovery budget as everything else in your life.

This has a practical consequence people rarely act on. During a genuinely difficult period — a bereavement, a work crisis, a new baby — running a hard training programme and an aggressive diet simultaneously is asking your body to adapt to three stressors at once with reduced resources.

The mature response is to reduce one deliberately rather than to have it collapse. Usually that means moving to maintenance calories and cutting training volume by a third, while keeping frequency and intensity. You hold what you have, you keep the habit, and you resume properly when there is capacity.

Attempting to push through all three tends to end with abandoning all three.

Breathing, and why it is not nonsense

Slow breathing practices have a reputation problem, partly because of how they are marketed. The underlying mechanism is straightforward and physiological.

Extending the exhale relative to the inhale increases parasympathetic activity via the vagus nerve, which lowers heart rate and reduces sympathetic arousal. This is measurable rather than mystical. Practices built around a longer out-breath than in-breath — five seconds in, seven or eight out, for a few minutes — reliably produce the effect.

The evidence for slow breathing improving perceived stress and some physiological markers is reasonable. The evidence for elaborate proprietary protocols being superior to simply breathing slowly is not. It costs nothing and takes five minutes, which is a favourable ratio even for a modest effect.

The practical version

If you are stressed and your midsection looks worse, the likely explanation is: you are retaining water, eating a few hundred more calories a day than you think, sleeping badly, and moving less.

None of that requires a supplement. All of it requires either fixing the sleep or fixing the stressor — and it will resolve considerably faster than you expect once one of them shifts.