It's a common lament among those of us trying to lose weight: When it comes to the food we choose, it often feels like we're thinking with our stomachs instead of our brains.

New research published this week suggests that this notion might be uncomfortably close to the truth.

According to team of neuroscientists in Portugal and Australia, bacteria in the guts of animals may be chemically communicating with the brain in such a way as to impact animals' dietary choices. The research paper, published today in the open-access journal PLOS Biology, concludes that bacteria actually “speak” to the brain, influencing decisions and behavior — in some cases quite radically.

If “gut” seems like an imprecise term, note that in this context it's actually referring to specific portions of the intestinal tract, including the stomach and intestines.

The study was carried out using fruit flies, which have proved remarkably useful over the years in initial experiments of this sort. Hoping to better understand the interactions of the brain and the gut, scientists fed the fruit flies sustained diets lacking certain essential nutrients.

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For example, the research team used a synthetic formula to remove critical amino acids that are otherwise found in natural foods. Like almost all animals, including humans, fruit flies need certain amino acids to serve as the building blocks of proteins that the body cannot otherwise create.

In a series of experiments, the researchers found that the removal of any essential amino acid caused a behavioral change, triggering a significant increase in the flies' ingestion of protein-rich food.

In some cases, the gut bacteria stopped the flies from developing an appetite for the missing nutrients and even changed their physiology to function without them.

“The bacteria literally reprogrammed the body's nutritional needs, to the point that they even safeguarded the flies' fertility, which would otherwise have been abolished by the low quality of the diet,” said researchers in a summary statement.

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Fruit flies have five main bacterial species in the gut while humans have hundreds of different species. By using these simple animal models, scientists can begin to understand the more complex interactions that, down the line, may prove critical to human health.

One thing the researchers don't know, but are very curious to find out, is how exactly the bacteria communicate with the brain to alter appetite. Previous studies of the gut have established a relationship between diseases like obesity and the gut's microbiome, which refers to the composition of microorganisms in a particular environment.

But precisely how bacteria and the brain communicate remains a mystery. Researchers suspect that some kind of chemical exchange is involved, but no one knows for sure. Still, in science, knowing what you don't know is still a kind of progress.

“In sum, this study not only shows for the first time that gut bacteria act on the brain to alter what animals want to eat, but also that they do so by using a new, unknown mechanism,” the researchers said.

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