Your Gut Health and it's host microbes (or are we really the host?) play huge roles in the majority of our physiological processes. Keeping them balanced through diet is in our best interests for maximizing health.

Rundown of this article:

• Understanding the importance of gut bacteria and your health
• Your gut talks to your brain. (Not just stomach growls)
• How you eat determines the majority of your overall gut health

Picture an alien that lives within you. Matter of fact, picture a whole community of aliens living within you. All of them live in a  tube that determines where the food you eat goes, how it is disposed, how you will respond to imposing sickness, and if you will gain more fat.

And is also responsible for the butterfly feeling you have in your stomach.

Yes, we are talking about your gut.  Which has also been referred to you as your 2nd brain. Inside of our stomach we have a separate nervous system (enteric nervous system), and a plethora of host organisms that play a major role in nutrient absorption, hormonal responses, neurotransmitter production and many other key operations within our bodies.

Our gut microbes outnumber our own original cells 1000:1. To comprehend the immense number of intestinal microbes we can reference parts of the human body to paint the picture. If our total human cells covered the outside of our bodies-cells that carry our DNA in the nucleus would only cover the big toe while our microbes would consume the rest of our bodies. Our microbial community has multiple interactions in our health but in this article we will discuss the role they possibly have in our overall body composition. In this article you will understand what the microbiota is, understand the role of the gut-brain axis, and how these factors effect our ability to accumulate fat.

Wait, the Micro What?

The gut microbiota is a complex system of primarily single-cell bacteria alongside eukaryotes and viruses. Our microbiota environment is effected by multiple factors such as but not limited to stress, antibiotic use, environmental pollutants, and diet. Although there are multiple factors that can influence the gut, the largest role is diet. In many studies, the microbiota can show noticeable changes in a as little as a day. Inside your gut, the microbes get to work by digesting foods, fermenting non-digestible carbohydrate and unused macronutrients, maintaining the intestinal epithelium (lining of our intestines), and defending our bodies against pathogens. The microbiota also aids vitamin synthesis (A, C, folate, and niacin) as well as producing amino acids.

So we now know that the gut is made of trillions of microbes, more than all the stars in the universe (cool fact, I know), acts as a line of defense against outside pathogens, while playing a key role in digestion and vitamin synthesis. Great, but the extents of the gut do not end there; our microbial community improves the strength of our epithelium to protect the rest of our body from pathogens. To explain the importance of this let's key in on something we are all familiar with. A toilet. By necessity we all are familiar with the fact that the toilet takes in waste, flushes it through the pipes and the waste products are pushed out for disposal. If those pipes leaked or the toilet overflows, well we would have a problem. Our house would be damaged (and smell less than desirable.)

The overflowing toilet or leaky pipes is synonymous to our gut harboring unhealthy and/or have an imbalance favoring unhealthy bacteria. Since healthy microbes enhance gut barrier, the opposite occurs when we have an unhealthy gut environment and we can develop "leaky gut" which allows toxins to seep through our gut walls and wreck havoc on our bodily systems. Chronic inflammation and insulin resistance develops from the effects of open gut permeability. As these toxins spill into our body creating a state called endotoxemia, our immune system responds with low grade inflammation to encapsulate the toxins. Inflammation is fine when acute, but as time progresses we pose the threat of developing chronic low-grade inflammation which encourages lovely side effects such as; diabetes and cardiovascular disease. How does this effect your body composition? I will explain soon but first we will briefly go over the gut-brain axis that will tie in completely to how our microbes effect body composition.

Gut-Brain Axis

Our brain and the microbes in our stomach are directly linked via the gut-brain axis (GBA). In short, the microbial community in our gut has direct communication with key centers in our brain that are linked to our emotional and cognitive centers. The purpose of the GBA is to monitor and integrate gut functions that link our emotional and cognitive portions of the brain to intestinal functions that include immune activation, intestinal permeability, enteric reflex, and enteroendocrine signaling. Communication of the brain and gut commences through the hypothalamus, brainstem, and vagus nerve indicating direct access to our brains. Our hypothalamus is a very small portion of our brains that is responsible for key physiological functions such as temperature regulation, hunger, mood, and sex drive.

The hypothalmus controls the pituitary gland by releasing neurohormones that either start or stop the secretion of pituitary hormones. The following hormones are released by the hypothalmus that play key roles in our physiological processes:

• Corticotropin-releasing hormone (CRH): Plays a major role in stress response and cortisol release. When the hypothalamus releases CRH, the pituitary gland stimulate the adrenal glands to release corticosteroids such as cortisol.
• Anti-diuretic hormone (ADH): Controls fluid retention by increasing or decreasing water absorption by the kidneys
• Oxytocin: Participates in various processes including body temperature, orgasms, and sleep cycles
• Thyrotropin releasing hormone (TRH): TRH initiates the release of thyroid hormones that regulate metabolism, energy levels, alongside growth and development

The microbes of our gut have direct communication with our hypothalamus that can alter our physiological states. Below, we will see some of the ways of the how. After reading this article, I suggest to read about the hypothalmus and the HPA axis (Hypothalmus-Pituitary-Adrenal Axis) since it has much to do with many of our chronic diseases. If you are highly interested in all of the functions of the hypothalamus, you can read an in-depth PDF by clicking this link.

How GBA and Microbiota Effect Body Composition

To understand how the microbiota effects our body composition, it is important to know in which way our gut biome ferments and responds to our dietary intake. Each of us have  our own unique micro-genome that is as individual as a fingerprint. Yet, we have the same dominate phylum of bacteria that accommodates our gastrointestinal tract; bateriodetes and firmicutes. From human and animal studies, there is a strong correlation of bacteriodetes being higher in ratio of dominant bacteria in healthy guts while firmicutes are higher in the "unhealthy" gut. This imbalance occurs when an individual eats a diet high in fats and sugars (in literature "Western Diet") that is primarily based on processed foods. This shift can begin to occur in as little as 24 hours post dietary intervention.

As stated earlier, our gut flora ferments indigestible carbohydrates in which create bi-products due to metabolism. Most notably seen is the production of short chain fatty-acids (SCFAs) that are utilized in our physiological processes. Of these SCFAs, the most common are acetic acid, propionic acid, and butyric acid which are later utilized as ligands which bind to satiety peptides that influence our hunger.  In other words, SCFA production impacts our feelings of satiety or "fullness" from the meals that we eat. Important peptide hormones that influence our food regulation centers in our brain are stimulated by SCFAs. For example, Peptide YY (PYY) and glucagon like peptide-1 (GLP-1) are key players in the role of reducing food intake. Both hormones are originated in L-cells of the intestine as well as the colon and ileum of the gut which travel up the vagus nerve to stimulate the appetite and anorexigenic neurons of hypothalamus to inhibit feelings of hunger.

Lack of SCFAs are not the only pathway fat accumulation is provoked. Diminishing microbial diversity can drive the fat accumulation process as well. AMPK (activated protein-kinase), a key enzyme that activate mitochondrial break down of fatty acids, is inhibited reducing the usage of fat stores as energy. Increased circulating lipopolysaccharides (LPS) also contribute to weight gain due to endotoxemia and increased insulin resistance.

The Take Home Message

Eating foods that are beneficial to our bodies and the bacteria that reside within our gut is a key to maintaining our health and a sexy body composition. Since the onset of a negative bacterial balance is primarily induced by the foods that we eat. The following can be utilized as a guide to keep your gut in check. 

• Exercise regularly. Exercise encourages the modulation of body composition and the excretion of anti-inflammatory cytokines that are beneficial to your health. (Click Muscle Talks for another article on this)
• Macro-nutrient quality, quantity, and ratio is important. Diets with modest amounts of protein (25%-40%) of total energy expenditure alongside non-processed carbohydrate and fats fair well for your gut.
• Eat your fiber. An adult should be intake 25g-38g of fiber daily. Dietary fiber intake encourages the fermentation of beneficial SCFAs.
• Micronutrients are key. Eating processed foods devoid of nutrients is bad news for your gut. 
• Slow down (in Utopia, eliminate) the consumption of processed foods and simple sugars as these encourage negative bacterial overgrowth
• Probiotics can be beneficial. Primarily those of the genera Lactobacillus and Bifidobacterium
• Ease Prebiotic foods into your diet. Prebiotics, foods that encourage beneficial bacteria, feed the growth of diverse and beneficial bacteria. Fermented foods such as kimchee, sourkraught, yogurt and pickles are great. If fermented foods aren't your taste, garlic, asparagus, onion, or any vegetable that carries a great fiber load.

As our parents have said, you are what you eat. Which can easily be translated to "we become what we eat." Although we cannot control our genetics or the environment we spend most of our lives in, what we can control are the foods we decide to consume. We are not only feeding ourselves, but also the bacteria that reside within our intestines which control many key physiological processes of our bodies. Although this article is based around body composition, our overall health is determined by our gut biome. You can easily be thin, intake unhealthy foods and end up with a metabolic disease that impedes your quality of life. Eat well. Live well. Feel well.

In my research based around this article, I ran into many aspects of health that the gut microbiome influences. Below will be articles based on other aspects of human function that have a strong influence by the gut. Click the coordinating links below to access the easy to read articles.

• Depression
• Anxiety
• Sleep 
• Autism
• General info of interaction with brain

References

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2. Foerster, J., Maskarinec, G., Reichardt, N., Tett, A., Narbad, A., Blaut, M., & Boeing, H. (2014). The Influence of Whole Grain Products and Red Meat on Intestinal Microbiota Composition in Normal Weight Adults: A Randomized Crossover Intervention Trial. PLoS One, e109606.
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