You’ve probably heard that yogurt is good for you because of its “live and active cultures.” Is this valid, or is it just another nutrition catch phrase designed to get you to buy a product? Turns out, these bugs may actually help boost your mood. Let’s see how.
The human microbiome is the collection of microorganisms (including bacteria, viruses, archaea and eukaryotes) that take up residence in a human host. The makeup of this population shifts in response to factors such as injury, illness, stress, and diet; no two people have a microbiome that is exactly the same. You’ve probably heard the world “probiotics” being tossed around; this refers to strains of bacteria that benefit their host. Prebiotics, by contrast, are indigestible carbohydrates that serve as food for those good bacteria.
Although bacteria are present throughout the body, the greatest number and variety of species live in the intestines. Humans are born with a sterile intestinal tract, which is colonized by microbes as we feed and interact with the outside world. By about two and a half years of age, a child’s intestinal microbiota will be similar to an adult’s, with around 300-500 species of gut bacteria. It’s crucial that babies are exposed to “foreign” materials from the outside world so that they are able to develop this diversity — a failure to do so may lead to increased susceptibility to disease and allergies later on in life. The relationship between humans and many species of microorganisms in the intestines is mutualistic, meaning that both benefit. The microorganisms are able to feed and reproduce, and they in turn help us by protecting cells from injury and death, producing important nutrients such as vitamin K and some B vitamins, aiding in digestion, and maintaining the epithelial lining of the gut. They can also reduce inflammation and enhance the immune response.
There is a growing body of evidence that suggests that gut microbes can also affect the brain. The connection between the digestive system and central nervous system is well established; the gut has been called “the second brain” due to its approximately 100 million neurons. Communication between the gut and the brain is bi-directional, giving rise to the term “gut-brain axis.” Over 80% of the body’s serotonin, a neurotransmitter that regulates mood, sleep and appetite (among other things) is produced in the gastrointestinal tract, and gut microbes are hypothesized to play a key role in that process. They may also stimulate the vagus nerve, which communicates between the enteric (gastrointestinal) and central nervous systems. Studies done with both mouse and human subjects have shown associations between gut microbiota and brain activity. They suggest that probiotics may help with psychological disorders such as anxiety and depression.
So, what should we eat? I’m not advocating that you go out and buy a bunch of probiotic supplements (unless your doctor has specifically suggested that you do so). The research on probiotics and human health is still in the early stages, and the Food and Drug Administration (FDA) does not require supplements to be proven safe before they go on the market, so some of their effects may be unknown (read more about how the government regulates probiotics here). However, there are many different foods that may improve the profile of your microbiome. I’ll leave you with a list of a few; hopefully you’ll find something new to try!
Probiotic foods: the following foods contain strains of beneficial bacteria
Yogurt: Look for brands with “live & active cultures,” but watch out for added sugar!
Kefir: A sour, fermented milk drink with a name that’s hard to pronounce
Sauerkraut: A cabbage dish that’s a great starter for people interested in fermenting foods at home
Miso: A Japanese paste made from fermented soybeans, often used in soup
Kombucha: An effervescent tea-based fermented drink (It usually runs for around $3 a bottle and I personally love this stuff, so I’m looking into making my own)
Prebiotic foods: the following foods contain fructans, a type of dietary fiber that can promote the growth of beneficial bacteria
Jerusalem artichokes: Eat them roasted with sea salt and garlic!
Garlic: Try it raw on buttered toast; eating garlic raw may help to preserve some of its disease-fighting compounds
Onion: Learn the best ways to slice and dice this flavorful aromatic
Celery: Don’t tell me that you don’t miss ants on a log
Bananas: Substitute them for ice cream (seriously, try it)
References
Alcock, Joe, Carlo C. Maley, and C. Aktipis. “Is eating behavior manipulated by the gastrointestinal microbiota? Evolutionary pressures and potential mechanisms.” BioEssays 36.10 (2014): 940-949.
Carabotti, Marilia, et al. “The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems.” Annals of Gastroenterology 28.2 (2015): 203.
Guarner, Francisco, and Juan-R. Malagelada. “Gut flora in health and disease.” The Lancet 361.9356 (2003): 512-519.
Mayer, Emeran A. “Gut feelings: the emerging biology of gut–brain communication.” Nature Reviews Neuroscience 12.8 (2011): 453-466.
“Overview.” NIH Human Microbiome Project, 2016, http://hmpdacc.org/overview/about.php. Accessed 2 November 2016.
Rhee, Sang H., Charalabos Pothoulakis, and Emeran A. Mayer. “Principles and clinical implications of the brain–gut–enteric microbiota axis.” Nature Reviews Gastroenterology and Hepatology 6.5 (2009): 306-314.
Tillisch, Kirsten, et al. “Consumption of fermented milk product with probiotic modulates brain activity.” Gastroenterology 144.7 (2013): 1394-1401.