The Power of the Gut, Outside of the Gut

“The gut is not like Las Vegas. What happens in the gut does not stay in the gut.”

- Dr. Alessio Fasano, Gastroenterologist

There was once a time in the nutritional realm that gut function was considered to solely impact upon digestive disorders, like bloating and constipation. However, the times they are a-changin’, as emerging research begins to highlight the fascinating ways the gut can influence the functioning of the entire body. A run down of influence of the gut in immune function, body weight and mental health only adds to the ever-growing list of reasons why 2016 is the year of gut health (sorry Kanye).

Immunity

Over 80% of body’s immune cells reside in the gut. The microbes living alongside these immune cells are vital to the introduction, training and functioning of a kick arse immune system. If you haven’t yet learnt about the somewhat disgusting, somewhat amazing world of bacteria currently within you, refer here.

Your gut microbes provide information regarding the ingestion of harmful substances (for example the flu virus, or, the bacteria living within a 6 day old burrito), in order to stimulate the immune system as needed. When fed the right foods, gut microbes also produce molecules that regulate immune function and reduce inflammation, such as Short Chain Fatty Acids (SCFAs).

Given the large importance of these very little microbes to immunity, it is logical that abnormal gut microbe composition (a condition known as “dysbiosis” in the land of gut health) has been linked with lowered immunity and autoimmune disease. It is hypothesized that the rise antibiotic use, cesarean births, poor dietary habits and hyper-sanitation (shout out to you Dettol) in high income countries have resulted in gut compositions which lack the strength and diversity to establish balanced immune responses.

Research has identified striking differences between the microbiomes of western children to those of rural Africa, where modern autoimmune diseases such as allergies and asthma are essentially nonexistent. African children, eating a very high fiber diet, have greater gut microbe diversity and produce significantly more SCFAs, both of which are critical for immune function.

The power of the gut-immune relationship has also been demonstrated in a recent review that found the composition of microbiome can influence the effectiveness of vaccines in the body. Vaccines were shown to be less effective in individuals with gut dysbiosis, because the immune system was already preoccupied with dealing with existing gut inflammation. This discovery has exciting implications for future research projects that will investigate if the gut can also influence the effectiveness of other medications, supplements and even food.

Weight

The gut is also thought to exert powerful effects on metabolism and resultantly, body weight. We know that the bacterial gut compositions of normal weight vs obese people are very different. Fecal transplant studies (yes, that is what you think it is) in rats have provided fascinating data of the power of the microbiome to influence weight. A 2013 study published in Science, transplanted gut bacteria from obese and lean pairs of twins into germ free mice. The results showed mice injected with bacteria from fat twins grew fat; while those injected with bacteria from lean twins stayed lean. Furthermore, another study in Nature demonstrated that mice injected with obese gut microflora actually extract more calories from the exact same food than mice with lean microflora. This research provides not only reasoning for the observed changes in these rats, but potentially reasoning for why humans do not lose even when following a calorie restricted diet.

Recent research is showing these results are applicable among humans. Researcher Max Nieuwdorp has completed double blinded fecal microbiota transplantation (FMT) on Type 2 diabetics with lean donors. The study found FMT from Lean male donors into males with metabolic syndrome resulted in a significant improvement in insulin sensitivity in conjunction with an increased intestinal microbial diversity. Scientific America explain recent findings in saying;

“the wrong mix of microbes, it seems, can help set the stage for obesity and diabetes from the moment of birth.”

It is a powerful idea for future health intervention that changing the microbiome may change the way food is metabolised, the occurrence of obesity and development of chronic disease.

Mind

While it is well established the brain signals the gut to exert effects over the Gastrointestinal Tract (GIT), it has recently been shown this relationship goes both ways. The gut can effect the brain too. Mark Lyte in Advances in Experimental Medicine and Biology explains:

“The bidirectional interaction [of the gut-brain axis] is important not only in normal gastrointestinal function but also plays a significant role in shaping higher cognitive function such as our feelings and our subconscious decision-making.”

When considered physiologically, this idea is actually quite intuitive. The gut produces many molecules that inevitably end up in the brain, and can effect on mental state of an individual. For example, 90% of serotonin, the body’s feel good neurotransmitter, is produced in the gut. It therefore makes sense that a healthy gut environment is vital in facilitating a healthy mental state. Likewise, it is no surprise that dysbiosis is beginning to be associated with many neurological disorders, from Autism to Alzheimer’s.

For a deeper insight, check out Neuroscientist David Perlmutter explaining some of these recent findings about the gut-brain connection:

[embed]https://www.youtube.com/watch?v=ucAJ0U5Veis[/embed]

Or, if you prefer your gut information delivered in a Scottish accent, I can offer you a Ruari Robertson Ted Talk.

Obviously, the presented information is classified as emerging knowledge. There is still much more to learn. Although mechanisms are unclear, the idea that the gut can change the brain, immune response and body weight is too powerful to ignore. We have known for a long time now that plant foods, fiber, probiotics, mindful eating habits, and the limitation of antibiotics are all good things. Now, with the impact of such gut health practices having the potential to extend far beyond the bathroom, there has never been a better time to start lovin’ your gut.