Probiotics: A Surprising Way to Beat Stress

Those trillions of microbes that live in your body—sorry!—have an astonishing influence on your state of mind and may affect your waistline

by Diane Lange
Photograph: Illustrated By Aad Goudappel

Have you ever been hit with gas pains while you were stressed out? Or battled butterflies in your stomach before doing something daunting? If so, you’ve experienced the chemical and electrical communication that goes on between the brain in your head and the one in your digestive tract, which is known as the small or second brain.

The brain in your gut is not a discrete organ like the one up top; it is a network of nerves within the layers of tissue lining the walls of your digestive tract. This network’s main job is to regulate the action taking place along the 30-foot tube extending from your esophagus to your anus and all the stops along the way: stomach, small intestine and large intestine. Long aware of the role these nerves play in the second-brain communication system, researchers have discovered a surprising new player—actually, about a trillion new players: the bacteria that live mainly on the inner walls of the large intestine.

These diverse bacteria perform several useful functions, such as digesting fiber, making vitamin K and some Bs and helping fend off the small amount of bacteria in your gut that could, in large enough numbers, make you sick. The “good” bacteria control the “bad” bacteria, either by producing substances that inhibit or kill the pathogens or by crowding out the troublesome bugs so it is difficult for them to adhere to the walls of the large intestine, says Kelly Scott Swanson, PhD, an associate professor in the department of animal sciences at the University of Illinois at Urbana-Champaign. Of the thousand or so kinds of bacteria in the gut, the most beneficial are probably the genera Lactobacillus and Bifidobacterium, notes Shekhar Challa, MD, a gastroenterologist in private practice in Topeka, Kansas, and author of Probiotics for Dummies. The term probiotics refers to good bacteria that live in food and certain supplements.

Researchers have known for years that stress can really rock this bacterial world. When your big brain senses a threat, glands pump out stress hormones that, among other things, trigger several chemical responses in your gut. As a result, the balance of good and bad bugs may be altered in favor of the -disease-causing bacteria, says Michaël Messaoudi, scientific and medical director of ETAP, a research laboratory in -Vandoeuvre-lès-Nancy, France. One study, for example, found that a hormone you produce when you’re stressed, norepinephrine, increases the virulence of Escherichia coli, a well-known pathogen. Another bad boy, Campylobacter jejuni, which causes the most common type of infectious diarrhea, may also surge when you’re under pressure.

The big news: In the past couple of years, scientists have discovered that just as the brain alters the gut bacteria, so too can these bacteria influence the brain. Not only do stress and your moods affect the functioning of your gut, but the bacteria in your large intestine may affect your mood and your emotional response to stress. For instance, animal experiments have shown that rises in Bifidobacteriaincrease levels of tryptophan circulating in the blood. Tryptophan is a precursor of the feel-good neurotransmitters serotonin and dopamine.

Probiotics as Prozac

If the bacteria in your gut can affect your mind, is it possible to manipulate these bugs to bring about desirable changes? A French team led by Messaoudi believes the answer is yes. The researchers gave healthy but moderately anxious people a daily probiotic supplement that contained Lactobacillus helveticusand Bifidobacterium longum. After 30 days, the volunteers who had taken probiotics showed decreases in anger and depression and an increased ability to solve problems. A later analysis showed similar mood-lifting effects in subjects who were less stressed. 

First published in the April 2013 issue

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