We are not alone: How the bugs in our gut influence our eating habits.

Your gut is literally teeming with microorganisms, the majority of which are bacteria. Indeed, the single celled squatters residing in our gut are estimated to outnumber our own cells 10:1 (this means that your body contains ten intestinal microorganisms for every one of its own cells!). Although these figures may make you feel uncomfortable, there is nothing sinister about our resident bacterial tenants; in fact scientists believe that the relationship we have with most these bacteria is actually beneficial. These bacteria or ‘microbiota’ help us absorb important nutrients from our food whilst also boosting the guts immune system, making them pretty much indispensable.

However, not all gut bacteria are alike. We know that, just as everyone expresses their own individual compliment of DNA , each individual also houses his or her own host of gut microorganisms. The specific compliment of bacteria resident in your gut depends heavily on environmental factors such as diet and is also liable to change throughout the course of a lifetime. Interestingly, as with DNA, different compliments of bacteria confer different properties to the host, some less favourable than others.

Work with mice suggests that certain types of gut microbiota may make an individual more prone to weight gain. This idea stems from work with three separate groups of mice: fat mice, lean mice and germ-free mice (mice with no detectable gut microorganisms). Scientists found that, unlike normal mice, germ-free animals did not gain weight when fed a high fat ‘Western’ diet. In fact, these mice needed to eat more than normal animals just to maintain a healthy weight. This is presumably because their lack of intestinal bacteria made it harder for them to absorb nutrients from their food. The researchers then moved on to investigate how these germ-free animals responded to infection from different compliments of gut microbes. They infected two separate groups of germ-free animals with gut microorganisms taken from either fat or lean mice. Both infected groups gained weight, however, only animals infected with gut microbes from the fat mice became overweight. These findings indicate that the fat mice may carry a specific array of microbes which promote excessive weight gain.

This research raises the question of how bacteria living in our guts can influence the amount of food we eat and the amount of weight we gain? Findings suggest that by-products generated by gut bacteria can influence both the amount of nutrition absorbed from food and the way the gut signals to the brain telling us to stop or start eating. Since different groups of bacteria will influence these systems in different ways, it has been suggested that the type of bacteria you house could influence both your eating habits and the nutrients gained from the food you eat.

So how do these findings fit with what we already know about weight control and the gut’s microbiome? Although the overall picture emerging from this research area is complicated, there are a few things we can be quite sure of: Firstly we know that our gut microbiota are generally more beneficial than they are harmful (note that although germ-free mice seem resistant to weight gain, they are also much more susceptible to infection and do not live as long as normal animals). We now also know that not all bacteria are equal, with some appearing more beneficial than others. Finally it is widely accepted that the role bacteria play in weight control is just one part of a much larger picture involving genetics, diet and exercise. Therefore, although I don’t think we know enough to claim that ‘good bacteria’ can offer a miracle solution to weight loss, the possibilities for further research into this area are exciting, especially since the gut’s microbiome is easily altered by changes in diet and the use of pro and prebiotics.

Post by: Sarah Fox