Updated: Dec 15, 2020
Alcock, J., Maley, C., & Aktipis, C. (2014). Is eating behavior manipulated by the gastrointestinal microbiota? Evolutionary pressures and potential mechanisms. Bioessays, 36, 940-949.
Article Review Written By: Kristy Snyder Colling, Ph.D. and Robert Coben, Ph.D.
Article Link: https://pubmed.ncbi.nlm.nih.gov/25103109/
Ever wonder why you are craving certain foods? Having trouble mustering the self-control necessary to fight off the cravings? Your gut-bacteria may be to blame.
Bacteria cells outnumber human cells in the intestines 100 to 1. Good bacteria serve us well by helping us digest food and bolstering our immune systems. However, bad bacteria can affect everything from regularity to even mind-control – or at least hunger regulation and cravings.
It has been suggested that there is an evolutionary arms race going on in our guts amongst different kinds of bacteria. Like all organisms in any environment, the bacteria in our guts fight each other for nutrients and habitat. The kinds of bacteria that are in our guts depend on the nutrients that can be found in that environment. Some bacteria prefer fiber while others prefer carbohydrates and still others flourish on polysaccharides. Indeed, people in Africa who eat a mostly sorghum-based diet have gut bacteria that prefer cellulose, while people in Japan who eat seaweed have bacteria that specifically digest seaweed.
Because each bacterium has its preferred nutrient source, it is evolutionarily beneficial for them to devise a way of getting their preferred nutrients to the gut. Some do this by manufacturing neurochemicals that are analogs of the mammalian hormones that influence mood and behavior. Sometimes, this is beneficial for us. For example, breast milk may reduce infant anxiety because the bacteria found in breast milk produces a neurochemical (i.e., GABA) that activates the same pathways as anti-anxiety drugs, like valium. Other times it can be detrimental. There is evidence that specific gut bacteria influence anxiety and stress levels in mice. One study even found that a certain bacteria placed in the gut of mice can influence their risk-taking behavior, making them less afraid of the smell of cat urine and, as such, more likely to get eaten.
In humans, the hormones produced by bad bacteria influence the vagus nerve, which controls hunger and food intake behavior. This means that the bacteria in our guts can influence our hunger, making us want to ingest more food. When there is excess energy in the gut (i.e., more calories than we need), it facilitates bacteria growth. Bacteria can also influence the kinds of food we crave, making us crave the kinds of foods that the largest population of bacteria residing in our guts specialize in.
When there is more diversity among gut bacteria, the effect of any particular kind is reduced because the various strains are keeping each other in check. However, when the population of one kind grows to a majority it has greater and greater influence – perpetuating the cycle of increased calorie intake and increased cravings for the desired nutrient source. That is why having more diverse gut bacteria is better than having more homogenous populations. Homogeneous populations of gut bacteria are often found in people who eat the typical Western diet of processed foods and high sugar and fat contents. Alternatively, heterogenous populations of gut bacteria are found in people who eat a varied diet of lean proteins and low carbohydrate vegetables.
The good news is that the kind of bacteria in the gut can be affected by dietary changes in as little as 24 hours. If you would like to take control of your nutrition back from your gut bacteria, please contact us. Our health coaches would love to talk to you about our program.