You Act What You Eat: How Gut Microbes Modify Our Behavior

Photo by Iulian Valentin.


by Monica Thunder

on March 30, 2015

We are what we eat — “we” meaning you and your microbiome, or the trillions of microbes living in your gut.

According to a recent study published in Biological Psychiatry Journal (BPJ), we also act and feel what we eat. High-fat, high-sugar diets change the composition of the microbiome, and it can seriously get to your head — chemically speaking.

“This paper suggests that high-fat diets impair brain health, in part, by disrupting the symbiotic relationship between humans and the microorganisms that occupy our gastrointestinal tracts,” said Dr. John Krystal, Editor at Biological Psychiatry, in a Science Daily press release.

In the study, researchers at Louisiana State University implanted gut bacteria from mice with high-fat diets and controlled diets into mice with uncontrolled diets. Through behavioral observation, the researchers found the recipients of the high-fat diet microbiota displayed increased anxiety, impaired memory and repetitive behaviors.

Brain samples from recipients of high-fat diet microbiota also showed signs of inflammation in the brain. According to a study published by Journal of Neuroinflammation, neuroinflammation is linked to psychiatric disorders such as depression.

“Overall, these data strongly suggest that therapeutic manipulation of the microbiome, which should be highly responsive compared with existing clinical targets, could dramatically mitigate the prevalence and/or severity of neuropsychiatric disorders,” write the authors of the BPJ study.

According to the study’s authors, prior to the publication of this evidence, scientists knew obesity was linked to mental illness but were uncertain whether obesity itself or a side effect of obesity caused these disorders. The study’s results support the latter — a high-fat diet changes the composition of the microbiome and this shift, rather than an excess of fat, has a direct relationship with mental disorders.

“The present findings represent the first definitive evidence that high-fat diet-induced changes to the gut microbiome are sufficient to disrupt brain physiology and function in the absence of obesity,” write the study’s authors.

The exact mechanism by which the microbiome affects psychiatric disorders remains unknown, but there are a few prime suspects. According to a Live Science article, the vagus nerve — which conveys sensory information from the gut to the brain — may be the link between the gut and the brain. The microbiome may also affect the immune system, which potentially affects psychiatric abnormalities.

Researchers cultivated the high fat diet microbiomes by feeding mice pellets of D12492, a mouse-foot created by Research Foods, Inc. that has been the standard for obesity research since the 1990s, according to Research Foods’ website. D12492 is 60 percent fat, and is, according to the common literature, lard-based.

In his blog, The Daily Lipid, Chris Masterjohn — who holds PhD in nutritional sciences — notes D12492 in fact derives 32 percent of its fat from polyunsaturated fatty acids (PUFA). Some vegetable oils such as corn, safflower, sunflower, canola, and soybean oil contain concentrated amounts of PUFA. These oils frequently occur in the American diet, and soybean oil is a prominent ingredient in D12492.

According to a Natural News article, while small amounts of naturally occurring PUFA found in foods like fish, olive oil, and nuts benefit the body, consuming excessive PUFA can be toxic. In concentrated forms, PUFA poison mitochondria, inhibit the thyroid, impair cell communication and interfere with enzyme activity within the body. When it oxidizes within the body, it produces tissue-damaging free radicals. In the long term, these side effects may lead to increased aging, atherosclerosis, or cancer, among other harmful conditions.

While the fats that largely composed the mice’s diet in the study are proven to have a variety of negative side effects in addition to their relationship with mental illness, consuming different kinds of fats may not have such deleterious outcomes. A Swedish study presented at the 2014 annual meeting of the European Association for the Study of Diabetes shows that consumption of dairy fat may contribute to preventing type-2 diabetes. The study also showed that fat derived from red meats, such as lard, increases the risk of type 2 diabetes.

The study’s authors say further research on the subject is necessary.