The gut-hormone axis: 5 things everyone should know

By Niamh Wilson, ANutr, MSc Human Nutrition

 

Your gut might not be the first place you think of when it comes to hormones, but it's considered the largest endocrine organ in the body, producing more than 30 hormones, many of which respond to something you do every day: eating.

As food moves through your gut, specialised cells in its lining, called enteroendocrine cells, release hormones that help regulate digestion, appetite and blood sugar. Fibre travels further, to your colon, where it meets the microscopic world inside your gut: trillions of bacteria that ferment it into short-chain fatty acids. These signal back to the same cells, prompting the release of more gut hormones, including GLP-1.

This connection between what you eat, your gut microbiome and your hormones is known as the gut-hormone axis, and research suggests its reach extends well beyond appetite. Here are five things worth knowing…

 

1. The hunger hormone affected by sleep

Ghrelin helps regulate hunger, and most of it is made in the gut. Levels rise before meals, signalling to your brain that it's time to eat. Studies of sleep loss often find higher ghrelin alongside increased hunger, so feeling hungrier after a poor night's sleep may be partly biology, not just willpower.

 

2. 95% of serotonin is produced in your gut, but doesn't reach your brain

Around 95% of your serotonin is made in your gut, so it's easy to see why "your gut controls your mood" has become such a popular idea. But gut serotonin can't travel into the brain. It works locally, helping to move food through your digestive system.

That doesn't mean your gut and brain aren't connected. Gut serotonin can activate nearby nerves, including the vagus nerve, which carries messages between the two, although how this affects mood is still being researched.

3. Gut bacteria can help recycle oestrogen

Once your body has used oestrogen, your liver tags it for removal, and some is sent to your gut. There, certain bacteria can remove that tag using an enzyme called beta-glucuronidase, reactivating the oestrogen so it can be reabsorbed rather than excreted. These oestrogen-processing bacteria are known as the estrobolome.

4. A disrupted gut microbiome can impact oestrogen

This means a disrupted gut microbiome (often called dysbiosis) could change how much oestrogen is reactivated. In a 2024 trial, peri- and postmenopausal women taking a probiotic with beta-glucuronidase activity maintained their oestrogen levels over 12 weeks, while levels fell in the placebo group. But the research is early, and we don't yet know what an "ideal" level of this enzyme looks like, so supporting your overall gut health makes more sense than targeting one enzyme.

5. Your cycle’s impact on your gut

The conversation runs both ways. If your digestion shifts around your period, you're not imagining it: in one study, nearly three in four healthy women reported changes such as abdominal pain or looser stools. Progesterone is thought to slow the gut after ovulation, while prostaglandins, hormone-like compounds released as your period begins, can speed things up.

The takeaway

Think less about "balancing hormones" and more about supporting the whole system. There's still a lot we don't know, but a diverse gut microbiome is linked with better health, and it shapes the environment where much of this hormone signalling happens. That might look like:

• A fibre-rich, plant-forward diet, including prebiotic foods like onions, garlic, oats and apples

• Fermented foods such as live yoghurt, kefir and kimchi, which have been shown to increase microbiome diversity

• Probiotic supplements, which may play a supporting role, although effects depend on the strains used

• Cruciferous vegetables like broccoli and cabbage, which may influence how your body breaks down oestrogen

• Prioritising sleep, to help keep hunger signals steadier

Your gut and your hormones are in constant conversation. Start with variety on your plate.

 

References

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