Are you really in charge of your appetite and weight? It might seem a strange question, but new research suggests that we may not choose our own diets. Instead, the billions of bacteria in our guts drive us to consume the nutrients that they need to survive.
We need gut bacteria to help digest our food, keep our organs healthy and our immune systems strong.
Now it seems these bacteria also drive our appetite, cravings and moods to get us to eat what they want, consuming the nutrients they prefer, rather than simply living off what we might otherwise choose to eat.
This is the conclusion of a broad review of scientific studies, including laboratory tests on human cells and gut bacteria, as well as observations of human eating and behaviour. The authors, of the University of California, San Francisco (UCSF), concluded different species of bacteria need different nutrients. For example, some bacteria prefer fats, others want sugars.
‘Bacteria in the gut are manipulative,’ says Dr Carlo Maley, the study’s leader and director of the UCSF Center for Evolution and Cancer. ‘There is a diversity of interests represented in the microbiome (the community of trillions of ‘friendly’ bacteria in our bodies). Some are aligned with our own dietary goals, others not.’
So, while we may want to shed pounds by cutting down on, say, fats, our gut bacteria may decide otherwise and cause us irresistible cravings for fatty foods.
The authors believe the bacteria may do this by releasing chemicals into our gut that influence our appetites. Those signals could influence our bodies and behaviour, as the gut is linked by powerful pathways with our brains and hormonal systems, in particular the vagus nerve, which connects 100 million nerve cells in the digestive tract to the base of the brain.
In this way, they may alter our taste receptors, producing toxins to make us feel bad when we eat foods they can’t use, and releasing chemical rewards when we eat their favoured nutrients, says the study. These may not only affect our tastes but also our morale, it adds.