New research part-supported by the EU-funded FLIACT project has shown that gut bacteria ‘speak’ to the brain to control food choices, identifying two specific species of bacteria that have an impact on animal dietary decisions.
Now, in a paper published in the Opean Access journal ‘PLOS Biology’, neuroscientists have found that specific types of gut flora help a host animal detect which nutrients are missing in food and then finely titrate how much of those nutrients the host really needs to eat. ‘What the bacteria do for appetite is kind of like optimizing how long a car can run without needing to add more petrol to the tank,’ commented senior author Carlos Ribeiro.
The team conducted experiments using the fruit fly Drosophila melanogaster, a model organism that allowed the scientists to dissect the complex interaction of diet and microbes and its effect on food preference. First, they fed one group of flies a sucrose solution containing all the necessary amino acids. Another group got a mix that had some of the amino acids needed to make protein but lacked essential amino acids that the host cannot synthesize by itself. For a final third group of flies, the scientists removed essential amino acids from the food one-by-one to determine which was being detected by the microbiome.
After 72 hours on the various diets, flies in all three groups were presented with a buffet offering their usual sugary solution alongside protein-rich yeast. The results initially showed that flies deprived of amino acids showed decreased fertility and increased preference for protein-rich food. Indeed, the team found that the removal of any single essential amino acid was sufficient to increase the flies’ appetite for the protein-rich food.
The research team then tested the impact on food choices of five different species of bacteria that are naturally present in the guts of fruit flies in the wild. The results exceeded the scientists’ expectations: two specific bacterial species could abolish the increased appetite for protein in flies that were fed food lacking essential amino acids. ‘With the right microbiome, fruit flies are able to face these unfavourable nutritional situations,’ commented team member Zita Carvalho-Santos.
‘In the fruit fly, there are five main bacterial species; in humans there are hundreds,’ adds co-author Patrícia Francisco. This highlights the importance of using simple animal models to gain insights into factors that may turn out to be crucial for human health.
So the killer question was, how could the bacteria act on the…