Posted on 27 April 2022
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Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.
Why is this research important: The bacteria in our guts have a profound effect on many aspects of our health, so it’s important to look after them. What we eat affects which kinds of bacteria can thrive in the gut, but what about the reverse? Can the composition of the gut flora affect our eating habits? If so, there could be important implications for the prevention or treatment of obesity and metabolic diseases.
What did the researchers do: In this study, researchers wanted to see if introducing different bacteria into the guts of mice would influence their eating behaviour. They chose three rodent species with different feeding behaviours: the southern grasshopper mouse (a carnivore that eats insects), the white-footed mouse (an omnivore) and the montane vole (a herbivore). They then took 30 male adult lab mice that were germ-free – that is to say they housed no detectible microorganisms, including gut bacteria. They split them randomly into three groups of 10, and each group received gut microbiome transplants from one of the three mouse species described above, which were collected from the wild.
After a 7 day acclimatisation period, these mice were then offered a choice between two food sources. Both food sources had the same number of total calories, but one was low in protein and high in carbohydrates, while the other was low in carbs and high in protein.
Key takeaway(s) from this research: The origin of the microbiome transplants had a statistically significant association with the type of foods the mice in each group chose to eat. Mice receiving bacteria from the herbivorous mice voluntarily consumed fewer carbohydrates and more protein than either of the other groups. They also consumed fewer calories overall than the other groups.
They then analysed the gut bacteria of the lab mice to see how they differed, and to see if this could explain the mice’s different diet behaviours. They found that the bacteria transplanted from the herbivorous mice had a higher abundance of genes involved in the synthesis of certain amino acids. Of particular note, the genetic data suggested that these bacteria synthesised more tryptophan, and this was correlated with higher levels of tryptophan in the blood of recipient mice. Why is this important? Tryptophan is used to synthesise the neurotransmitter serotonin, which has been shown to be important in diet selection. For example, rats injected with serotonin eat fewer carbohydrates.
The mice receiving microbiomes from the herbivorous animals even had enlarged colons compared to the other groups, which is a trait common among herbivores. It has been documented that bacteria can remodel the structures of the gut, but this change could also have been a response to the mice’s diets.
This research provides further evidence that the gut microbiome composition can influence aspects of behaviour. The paper approached this subject from an ecological and evolutionary perspective, but the findings also have relevance for human health, assuming that they hold true in our own guts. They suggest that modifying our gut bacteria not only improves gut health, but could also serve as a tool to help us make better dietary choices.
The gut microbiome influences host diet selection behavior: https://doi.org/10.1073/pnas.2117537119