Dr Alcock, who is associated with the University of New Mexico in Albuquerque, said evidence from lower species seems to show that the interaction of the gut microbes with their host environment goes beyond a merely chemical interaction that affects the epithelial layer. Alcock, who was one of the speakers at the recent Probiota Americas event in San Diego, said microbes produce chemicals that are key parts of the body’s communication system. These signaling molecules have been shown to affect mammalian behavior in a number of ways.
One of the behaviors they theoretically can affect is eating. It has been demonstrated that the gut makeup of normal BMI people and those who are overweight or obese differs markedly. The microbial family Akkermansia, for example, is associated with a lower BMI. Is this because the dietary choices of people in that group tend to preferentially feed those microbes, or do the microbes secrete chemicals that predispose people to certain food choices? Or, on another note, could effecting a shift in the gut microbiome give a habitually depressed person a sunnier outlook?
Dr Alcock said these are intriguing questions, ones that have not yet been answered in people. A number of gut/brain axis studies have been done in mice, on eating, motivation and other behaviors, but Dr Alcock and other speakers at the event, which was hosted by NutraIngredients-USA, cautioned that pulling the chemical levers of a mouse brain and doing the same for the vastly more complex human organ are two different things.
“The best evidence comes from increasing knowledge that the bacteria in our guts when isolated from the colon produce neurochemicals such as reward chemicals like dopamine. We also know that gut microbes produce appetite peptides that are very similar to mammalian appetite peptides. So they are making neurochemicals and proteins that could potentially affect eating behavior. Whether they do that is not yet known, at least not for people,” Alcock told NutraIngredients-USA.
It’s a difficult area of study from a practical or ethical standpoint. If a certain microbiome makeup were in fact harmful, you can’t very well test it in people. But Dr Alcock said studies that compare gut microbial makeup among populations give clues as to what might be going on in humans.
“What we do know of the traditional human populations that still exist, groups like the Yanomami in the Amazon or the Hazda in Tanzania, these are hunter gathers that have way more diverse microbes in their guts than we do. They are not necessarily healthier, but they don’t get Western diseases. They don’t get asthma, we don’t see them dying from cardiovascular disease or strokes. And cancer risk seems to be lower,” he said.