I am a big fan of the Mediterranean diet, which is rich in oily fish, nuts, vegetables and legumes (such as lentils and red kidney beans). There’s a lot of research showing that this way of eating reduces your risk of heart disease and type 2 diabetes. And we also know that switching from a typical Western diet to a Mediterranean diet can be an effective way to improve your mental health, with studies showing that it reduces rates of anxiety and depression.


But there are a couple of downsides to the diet. Anyone who’s started eating more fibre-rich food (or fermented foods, such as sauerkraut) will know that you soon start producing much larger stools and far more wind.

Now, thanks to scientists from the Liver and Digestive Diseases Networking Biomedical Research Centre in Spain, we know just how big the effect is.

For their study, titled ‘Differential effects of Western and Mediterranean-type diets on gut microbiota’, they recruited 20 male volunteers and randomly assigned them to eating either a typical Western diet for two weeks followed, after a break, by a Mediterranean-style diet, or vice versa.

Towards the end of each phase of the study, the participants were asked to fill in a daily questionnaire that asked, among other things, how often they had passed wind, how bloated they felt and the number, shape and weight of their stools.

Faecal samples were collected, to look for changes in the gut microbiome and they had the volume of gas they produced accurately measured by collecting the gas (via balloons attached to the rectum) after eating a standardised meal of stewed beans.

So what did they find? Well, not surprisingly the change in diet had an impressive impact on the microbes living in the volunteers’ guts, with a shift towards more butyrate-producing types. This is a good thing, because butyrate is a short-chain fatty acid that’s a powerful anti-inflammatory and also helps support the health of the gut wall.

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Illustration of a man eating a Mediterranean diet and farting © Joe Waldron
© Joe Waldron

The volume of ‘colonic biomass’ (poo) increased by 60 per cent and the amount of gas also soared. They not only passed wind around seven times more each day, but each time they did it contained about 50 per cent more gas.

But can you get the health benefits of the Mediterranean diet without the social discomfort? Well, you might try eating seaweed.

A recent study published in the journal PLOSOne found that feeding cattle a particular type of red seaweed had a dramatic impact on the amount of methane they produced (at both ends). The importance of the study is that cattle (and other ruminants) have a big impact of greenhouse gas emissions, due to the amount of methane they produce, so anything that will cut their gas production has to be a good thing.

I’ve no idea if eating seaweed would have the same impact on humans, but I’m told that drinking seaweed tea, made by pouring boiling water over dried kombu seaweed, has a soothing effect on the gut.

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Dr Michael Mosley is former medical doctor, health writer and BBC presenter. He’s best known as presenter of Trust Me I’m a Doctor on BBC Two but has also written a number of bestsellers about personal health and medicine, including The Fast Diet, Fast Asleep and Fast Exercise.