100 Trillion Microbes Live In Our Guts – Here’s Why We Can’t Survive Without Them

One hundred trillion microbes inhabit our body’s inner spaces, living in our guts. Outnumbering our own cells by 10-1, their profound effects on our bodies and even our behaviour are only just becoming understood. The latest research has revealed that our lifestyles and diets have a major effect on these internal inhabitants.


‘They can make you fat, or thin; they can cause disease; but they’re also essential to life’


What do our microscopic passengers do for us?

A healthy mix of microbes living in our guts is essential to health. As well as having the ability to make you fat or thin, they can cause disease – even cancer – but they are also essential to life, making critical vitamins that we need to survive and helping us to digest our food. From an early age they are involved in training our immune system, and can send chemical signals to our brains that control mood, anxiety and appetite.


What foods can keep our friends healthy?

Our internal passengers appreciate a healthy balanced diet just as much as the human part of us, but some foods can feed your inner microbe – which is comprised of bacteria, fungi and viruses, or the microbiota, as researchers call it. Healthy people have very diverse internal microbial populations. Geneticist Cisca Wijmenga at the University of Groningen in the Netherlands led a large study into the effect of food on bacterial diversity in the gut. She found that people who regularly eat yogurt or buttermilk have a greater diversity of gut bacteria. Coffee and wine can be beneficial, as well as fermented foods such as sauerkraut and kimchi.


What grub should we avoid?

Whole milk, excess alcohol and a high fat diet can decrease microbiota diversity. Antibiotics can also decimate your inner microbes and cause diarrhoea by knocking out part of the population and allowing ‘bad’ bacteria to overrun the gut, with explosive consequences. The US military, concerned at high rates of diarrhoea in soldiers in Iraq and Afghanistan, offered rations fortified with friendly bacteria.


What about our lifestyles and physical activity?

New research published this month by US army researchers examined the gut wellbeing of Norwegian forces after four days of extreme Arctic training. The physiological stress experienced by the soldiers had altered the makeup of their microbiome with increases in harmful bacteria and decreases in beneficial bugs. The activity of the bad bacteria caused the walls of the soldiers’ guts to become leaky – temporarily damaging and inflaming this important barrier to infection. So, boosting the levels of good bacteria before training begins could help soldiers withstand the rigours of extreme exercise. This approach could also help endurance athletes.


‘The strong influence of the microbiota on the processing of food makes calorie counting problematic’


Can our internal bugs make us fat?

Variations in the gut microbe population have a major role to play in weight gain. Dr Jeffrey Gordon practically invented the study of human gut microbes – he’s known as the father of the microbiome. At his lab at Washington University in the US, pioneering studies involved transplanting microbiota from identical twins, one obese and the other lean, into sterile mice. Transplants of the bugs alone could transmit leanness or obesity into the mice. Obese mice gained weight on exactly the same diet that caused the lean mice to maintain a healthy weight. The obese twins had a microbiota that was much better at extracting calories from the same food intake. The strong influence of the microbiota on the processing of food means that there’s much more room for weight gain variation between two people on identical diets than we previously thought.


How does gut biodiversity affect our body fat and heart disease risk?

In another study, Dr Michelle Beaumont at King’s College London linked body fat to microbial diversity in twins’ faeces as part of a long term twin research programme. ‘There is a clear link between decreased bacterial diversity in faeces and markers for obesity and cardiovascular risk, particularly for abdominal fat,’ she said.


If our gut bugs can make us fat, could manipulating them be a route to the treatment of obesity?

The answer is probably yes, and millions of research pounds are exploring this as a possible cure for a very 21st century health epidemic. Since obese people appear to have a much less diverse range of gut organisms, the future could yield a pill containing a cocktail of microbes that could be taken to combat obesity.


How could probiotics and prebiotics help develop a healthy gut?

Probiotics are foods containing live bacteria, such as yogurt; but do they actually work? Professor Glenn Gibson of Reading University is an expert on probiotics. ‘Taking probiotics is safe and can help a lot of us,’ he says. ‘They can reduce the risk of us getting many different gut-related problems.’ Prebiotics deliver specific nutrients that can favour different species. As we understand more about how they interact with our bodies, it may become possible to change the balance of our own gut microbes, and reintroduce or enhance a healthy microbiome diversity.


WHAT NEXT? Download and listen to BBC Radio 4’s two-part Food programme devoted to the gut microbiome. Part One and Part Two


Advice is for information only and should not replace medical care or recommendations. Please check with your Doctor before embarking on exercise or nutrition regimes for the first time.