What is the gut microbiome? How Does It Affect Your Body
What is the gut microbiome?
Bacteria, viruses, fungi, and other microscopic living things are referred to as microorganisms, or microbes, for short.
Trillions of these microbes exist mainly inside your intestines and on your skin.
Most of the microbes in your intestines are found in a “pocket” of your large intestine called the cecum, and they are referred to as the gut microbiome.
Although many different types of microbes live inside you, bacteria are the most studied.
In fact, there are more bacterial cells in your body than human cells. There are roughly 40 trillion bacterial cells in your body and only 30 trillion human cells. That means you are more bacteria than a human.
What’s more, there are up to 1,000 species of bacteria in the human gut microbiome, and each of them plays a different role in your body. Most of them are extremely important for your health, while others may cause disease.
Altogether, these microbes may weigh as much as 2–5 pounds (1–2 kg), which is roughly the weight of your brain. Together, they function as an extra organ in your body and play a huge role in your health.
What does the gut microbiota do?
The gut microbiota provides essential capacities for the fermentation of non-digestible substrates like dietary fibers and endogenous intestinal mucus. This fermentation supports the growth of specialist microbes that produce short-chain fatty acids (SCFAs) and gases. The major SCFAs produced are acetate, propionate, and butyrate.
Butyrate is the main energy source for human colonocytes, can induce apoptosis of colon cancer cells, and can activate intestinal gluconeogenesis, having beneficial effects on glucose and energy homeostasis. Butyrate is essential for epithelial cells to consume large amounts of oxygen through β oxidation, generating a state of hypoxia that maintains oxygen balance in the gut, preventing gut microbiota dysbiosis
Propionate is transferred to the liver, where it regulates gluconeogenesis and satiety signaling through interaction with the gut fatty acid receptors. Acetate—the most abundant SCFA and an essential metabolite for the growth of other bacteria—reaches the peripheral tissues where it is used in cholesterol metabolism and lipogenesis, and may play a role in central appetite regulation.
Randomized controlled trials have shown that higher production of SCFAs correlates with lower diet-induced obesity and with reduced insulin resistance.22 Butyrate and propionate, but not acetate, seem to control gut hormones and reduce appetite and food intake in mice. Gut microbial enzymes contribute to bile acid metabolism, generating unconjugated and secondary bile acids that act as signaling molecules and metabolic regulators to influence important host pathways.
How does it affect our health?
We can carry up to 2 kg of microbes in our gut. Within the tens of trillions of micro-organisms that live there are at least 1,000 species of bacteria consisting of over 3 million genes. What is more, two-thirds of the gut microbiome – the population of microbes in the intestine – is unique to each individual. But do you know how your gut microbiota could be influencing your health?
Most of us are aware that the bacteria in our gut play an important role in digestion. When the stomach and small intestine are unable to digest certain foods we eat, gut microbes jump in to offer a helping hand, ensuring we get the nutrients we need.
In addition, gut bacteria are known to aid the production of certain vitamins – such as vitamins B and K – and play a major role in immune function.
But increasingly, researchers are working to find out more about how gut bacteria – particularly the bacteria that is unique to us individually – influence our health and risk of disease.
Perhaps most studied is how gut microbiota affects an individual’s risk of obesity and other metabolic conditions. In November 2014, for example, Medical News Today reported on a study claiming our genetic makeup shapes what type of bacteria reside in our gut, which may affect our weight.
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In this Spotlight, we take a look at obesity and some of the other – perhaps surprising – health conditions that may be driven by our gut microbiota.