Fat or thin: can the bacteria in our gut affect our eating habits and weight?
Our gut does more than help us digest food; the bacteria that call our intestines home have been implicated in everything from our mental health and sleep, to weight gain and cravings for certain foods. This series examines how far the science has come and whether there's anything we can do to improve the health of our gut.
When we can't lose weight, we tend to want to blame something outside our control. Could it be related to the microbiota - the bacteria and other organisms - that colonise your gut?
You are what you eat
Our gut harbours some trillion microorganisms. These are key in harvesting energy from our food, regulating our immune function, and keeping the lining of our gut healthy.
The composition of our gut microbiota is partly determined by our genes but can also be influenced by lifestyle factors such as our diet, alcohol intake and exercise, as well as medications.
The bacteria in the gut obtain energy for growth when we metabolise nutrients from food. So our diet is a crucial factor in regulating the type of bacteria that colonise our gut.
One key role of the gut microbiota is degrading the carbohydrates we can't digest into short-chain fatty acids. These help regulate our metabolism and are also important for keeping our colon cells healthy.
Changes in our diet can rapidly change the gut microbiota. Generally, a high-fibre diet which is low in saturated fat and sugar is associated with a healthier gut microbiome, characterised by a greater diversity of organisms.
On the other hand, diets high in saturated fat and refined sugars with low fibre content reduce the microbial diversity, which is bad for our health.
Our animal studies have shown that consuming an unhealthy diet for only three days a week has detrimental effects on the gut microbiota, even when a healthy diet is eaten for the other four days.
This may be because the gut microbiota are under selective pressure to manipulate the hosts' eating behaviour to increase their own fitness. This may lead to cravings, akin to your system being "hijacked" by your microbiota.