The moment we’re born, bacteria start setting up camp in our intestines. By the time we’re grown, our gut houses trillions of these tiny, single-cell organisms, which do everything from signal our body to digest food, fight bad bacteria and pathogens, and break down cholesterol.
In recent years, we’ve learned that these bacteria (collectively known as our ‘gut microbiome’) affect a whole lot more than whether we feel gassy or bloated. “There have been so many studies in the last few years that link the microbiome with all sorts of diseases, disorders, and health issues that you wouldn’t think are connected to your gut at all,” says Daniel Almonacid, Ph.D., Vice President of Research and Development at uBiome, maker of microbiome testing kits.
Below are five common health issues that trace back to your gut, along with expert recommendations for nourishing your microbiome (and overall well-being!).
1. Depression
“So many factors influence depression and mood disorders, but our guts are proving to be one of those factors,” according to Mahmoud A. Ghannoum, Ph.D., one of the most sought-after gut health experts in the world (he coined the term ‘mycobiome,’ which refers to the fungus and yeast in the gut). Though research is still developing, animal studies have found that a lack of bacteria diversity and overall vitality in the gut microbiome is “strongly associated with mood-relating behaviors, including major depressive disorder,” according to a 2018 review published in the Reviews in the Neuroscience.
Related: Can Your Diet Make You Depressed?
“The relationship between mood disorders and the gut is complex, but people with depression have been shown to have disturbances in their gut microbiome, specifically an increase in inflammation,” says Ghannoum. Much of the immune system is housed in the gut, and some research suggests that depression is primarily an inflammatory condition (meaning it’s caused by immune dysfunction).
Additionally, a 2016 meta-analysis and review published in Nutrients says that the healthy bacteria in our gut play a noteworthy role in immune function and influence our overall well-being, linking probiotic supplementation with a reduction in mood issues in people under the age of 60. Ghannoum recommends that those dealing with low mood add a probiotic to their routine and take up a meditation or mindfulness practice, which have been shown to stimulate the expression of anti-inflammatory genes.
The ‘gut-brain axis,’ a series of nerves that runs directly between our gut and brain and passes signals back and forth between the two, may also play a role in mood issues, says Josh Axe, D.N.M., C.N.S., D.C., founder of Ancient Nutrition and DrAxe.com, and member of The Vitamin Shoppe Wellness Council. The ‘feel-good hormone’ serotonin, for example, is actually produced in our digestive tract—and changes in its production and function have been implicated in mood disorders.
2. Anxiety
As with depression, the link between gut health and anxiety is also now being explored in preliminary animal studies. Thus far, the research suggests the gut-anxiety connection may stem from the relationship between our microbiome and gene regulators in the brain called microRNAs (miRNAs), which have been implicated in anxiety- and fear-based behaviors.
One study published in the journal Microbiome found that mice that grew up in a normal environment and had well-colonized microbiomes typically displayed normal miRNA function, while mice raised in sterile conditions—which hindered microbiome development—displayed dysfunctional miRNA activity in the pre-frontal cortex and amygdala. Interestingly, when researchers colonized the mice’s guts with healthy bacteria, their miRNA function normalized.
The influence of the gut microbiome on mirRNAs is important because “these miRNAs may affect physiological processes that are fundamental to the functioning of the central nervous system and in brain regions […] which are heavily implicated in anxiety and depression,” said lead researcher Gerard Clarke Ph.D., M.Sc., of the APC Microbiome Institute at University College Cork in a press release.
3. Obesity
Because they affect everything from digestion and how your body absorbs nutrients to feelings of hunger and satiety, the bacteria in your gut also play an integral role in weight management, says Axe. One study published in Gut, for example, found that increasing propionate (a chemical produced by the microbiome) increased levels of satiety hormones and warded off weight gain in overweight adults.
A recent study in the Journal of Clinical Endocrinology & Metabolism also identified a connection between four specific strains of intestinal bacteria (Blautia, Dorea, Ruminococcus, and SHA) and weight. The researchers analyzed the gut microbiomes and stool samples of over 600 people, and identified that differing levels of those four specific strains of gut bacteria, along with 19 other compounds, explained their varying BMIs, suggesting a relationship between these compounds, the gut microbiome, and obesity. “This means that future studies should focus more on how the composition of gut bacteria can be modified to reduce the risk of obesity and associated metabolic and cardiovascular diseases,” said study co-author Marju Orho-Melander, Ph.D. in a press release.
Experts agree that more research is needed to better understand how our gut microbiota influence our weight before probiotic supplements can be used as a preventative measure. However, Ghannoum does have some advice: “The same tips given to most people who need to lose weight are the same tips I give for improving gut health. Eat a wide variety of real foods.” After all, a well-nourished microbiome is a thriving microbiome.
4. Skin Diseases
In addition to the brain-gut axis, a concept known as the skin-gut axis is also emerging, says Ghannoum. “The intestinal microbiome relates to skin health in a complex communication network between the immune system, endocrine system, metabolic system, and nervous system,” says one review published in World Journal of Dermatology.
Essentially, this means inflammation that may occur because of imbalances in the gut microbiome can also manifest in skin diseases like rosacea, psoriasis, and atopic dermatitis.
One study published in Clinical Gastroenterology, for example, linked small intestine bacterial overgrowth (or ‘SIBO,’ which occurs when bacteria, residual food and bowel secretions, and digestive enzymes don’t move from the small intestine to the colon properly, and build up to an excess in the small intestine) with rosacea. When study participants (who had both SIBO and rosacea) were given antibiotics to address their SIBO, not only did the excess bacteria clear up, but the rosacea did, too.
As research develops, experts are addressing inflammatory skin issues by recommending a holistic approach to improving overall gut health. “A well-rounded diet and healthy lifestyle are the two most important factors when it comes to gut health, and therefore the gut-skin axis,” says Axe. “Nutrient-rich whole foods nourish the gut, while ultra-processed junk and chemical-laden artificial sweeteners disrupt it. And though research is still limited, some studies suggest that taking probiotics can enhance gut health and support healthy skin.” Axe’s recommendation: Eat well, minimize stress, and get plenty of physical activity and sleep.
5. Diabetes
According to Almonacid, a healthy gut microbiome may also help control blood sugar and mediate our risk of developing diabetes. In fact, though there’s much research to be done, decreased microbiome diversity has actually been linked with increased incidence of type 2 diabetes.
After measuring more than 800 people’s blood sugar levels (a major risk factor for type 2 diabetes), the researchers behind one Cell study found that the same meal elicited different blood sugar responses in different people (even when factors like age were taken into account) and suggested that the differences in the participants’ gut microbiomes influenced their abilities to respond to an influx of blood sugar. The study authors propose that diets designed to bolster the microbiome can influence the body’s ability to manage blood sugar, which would help healthy individuals avoid the disease and those with the disease better manage it.
Research also suggests the inflammation and dysfunction involved in type 1 diabetes may be related to the gut, with one Cell Host & Microbe study showing that infants predisposed to type 1 diabetes experienced a sudden drop in microbiome diversity, an uptick in inflammatory bacteria, and changes in gene behavior and stool content just before developing the disease.
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