Science from the gut

The link between the brain, the gut and forever

Our life urge is inextricably linked to the gut. It is through the gut that we receive macro and micro nutrients that sustain us. The gut is so entwined with the nervous system that it is called the second brain. In the Eastern studies like Tai Chi the gut is a reserve of energy mastered to bring long life and wisdom. While thinking allows us to plan and develop structure, for making decisions we often rely on gut instinct. We even spill our guts to confess and ease our conscience. Guts are a matter of life and death. And that’s what science from the gut is all about.

Core joy

As the strongest correlation with longevity to date is caloric restriction, overeating to obesity can arguably be viewed as a chronic death urge. Many obese people are also depressed, a problem that could well originate in the gut. The gut lining, like the skin, directly interacts with and protects us from toxins and microbes in the environment. We tend to think that substances enter the body at our mouth but they are not truly part of us until they cross the lining of the gut into the bloodstream. The largest grouping of nerve cells outside the brain is found in the gut, (over 100 million) producing thirty different neurotransmitters including serotonin, which is active in regulating mood, appetite, intestinal movement and sleep. Contrary to popular assumption, ninety five percent of serotonin is found in the gut and only 5% in the brain. Depression and constipation are common symptoms when serotonin production or delivery to the brain is inhibited. Serotonin is made from tryptophan, the only amino acid which is not consumed by muscle during exercise. Foods high in tryptophan such as turkey and activities like weightlifting naturally support high serotonin levels and increase metabolic rate. Both are key factors in reversing obesity and mild depression.

Core fitness

Our immune system has pathogen recognition molecules in the lining of the gut. One such molecule, TLR5, recognizes the protein flagellin present in nearly all mobile bacteria. Researcher Katherine Harmon found that mice born without this recognition molecule ate 10% more and had a 20% increase in body mass over mice that had functioning TLR5. Mice with no TLR5 who were placed on a restrictive diet developed insulin deficiency. Can we hypothesize that the beneficial bacteria in the gut that help us digest our food and provide us with essential vitamins also trigger a response in the body to stop eating?

Matam Vijay-Kumar and his associates found changes in the intestinal flora of TLR5 deficient mice indicative of metabolic syndrome. These mice then passed metabolic syndrome to normal mice through the transfer of gut microbes. Yann C. Klimentidis et al found that the obesity epidemic is not confined to humans. Obesity has not only spread to chimps and rodents living in research colonies and to domestic cats and dogs, but it has also spread to feral rodents. D. Hruschka at Arizona State University found that despite women viewing obesity as a source of shame, the more obese a person’s circle of friends the more obese she is likely to be. Researchers have suggested that social norms and behaviors are responsible for this increase in obesity. But is it possible that passive transfer of microbes may also be involved?

Core immunity

Another immune system receptor, NOD1, recognizes peptidoglycan molecules on the surface of bacteria in the gut. Thomas B. Clarke et al found that these peptidoglycan molecules prime the immune system throughout the body via messages carried from the gut to the bone marrow by neutrophils (white blood cells). These messages stimulate the bone marrow to produce more immune cells. Broad spectrum antibiotics kill the entire intestinal flora. This leaves the immune system weakened because there are no bacteria in the gut to send messages to stimulate the bone marrow to build the immune system, leaving the body vulnerable to other infections. Once the intestinal flora is replenished, NOD1 ligands restore the neutrophil function. With such strong scientific evidence, is it unreasonable to expect drug companies to include quality probiotics in their antibiotic regimes? Keren Buhnik-Rosenblau et al went further and showed that host genetics play a major role in the composition of an individual’s intestinal flora and suggest that targeted probiotics could be used to personalize medicines to support health and longevity.

Dr Javier Bravo and Professor John Cryan showed that mice fed with a lactobacillus probiotic were less stressed, had less anxiety and had reduced levels of cortisone (stress hormone). These scientists also showed a direct effect of a probiotic on brain chemistry. They have proposed a model for a three way communication “microbiome-gut-brain” via the vagus nerve.

This microbiome-gut-brain model opens the door to quantifying the impact not just of the internal interactions of our body’s systems, but also how they are affected by our physical interactions with each other. While eating habits that support our gut are vital,exercising our life urge requires more than just swallowing a handful of probiotics or eating healthily. If gut microbes are passively transferred when we’re in close proximity with each other, and if the weight of our friends impacts our own, we need to take notice of our “gut” connections. The company we keep truly does matter.

Melanie Radford worked in cellular pathology, immunology and genetics for 10 years and in science education and management for 20 years. A Fellow of the Royal Institute of Medical Laboratory Science in England, she holds Masters degrees in Management and Education.

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