Along the same lines, researchers in Ireland found that probiotics—in this case, daily sips of the good bacteria Lactobacillus rhamnosus—altered the behavior of mice placed in conditions that normally cause stress and depression. After a few weeks of the regimen, the mice were confronted with a maze, which normally creates high anxiety in a mouse. Yet the mice that had sipped the probiotic punch were as laid back as if they were on Valium, says John Cryan, PhD, chairman of the anatomy and neuroscience department at University College Cork, who directed these experiments. The treated mice also had lower levels of the stress hormone cortisol than their fellow creatures that didn’t get the Lactobacillus when stressed.
Cryan offers a theory for the calming effects of the Lactobacillus: The bacteria may secrete substances or interact with other substances in the gut that are taken in by the small brain and passed along the vagus nerve (which travels between the abdomen and the head) to the brain, where the chemical messengers activate receptors for GABA, a neurotransmitter that’s connected with relaxation. Another theory, he says, is that those substances act directly on the vagus nerve.
Building better bacteria
Does this mean you could overcome a case of nerves tomorrow by eating foods that contain good bacteria (such as yogurt) or downing probiotic supplements? The simple answer: We don’t know yet. “I can’t tell you to go to the health food store and get a certain probiotic pill to help your mood,” says Cryan, who notes that researchers are only beginning to figure out which strains of bacteria do what and to determine what doses are required to bring about desired effects.
Still, it makes sense to follow strategies that beef up the good bacteria in your gut: It might make you more stress resistant, probably will reduce inflammation in your digestive tract and will most likely lower your risk of developing type 2 diabetes.
The best starting point is what you eat. “Among the factors known to alter the profile of your bacterial world, diet is the strongest,” says Jane Foster, PhD, an associate professor in the department of psychiatry and behavioral neurosciences at McMaster University in Hamilton, Ontario. You can increase the amount of good bacteria in your body by consuming more foods that contain probiotics. Kefir, a fermented milk product, and cheese contribute probiotics, says Challa. Yogurt is a good source since, by the FDA definition, it contains Lactobacillus bulgaricus and Streptococcus thermophilus, and many manufacturers add other strains as well. Make sure the yogurt you buy has been refrigerated and the label confirms it contains “live” or “active” cultures (most supermarket brands are fine; frozen yogurts are iffier). Less obvious sources of probiotics include other fermented foods such as sauerkraut and kimchi (a Korean version of fermented cabbage) and naturally fermented pickles (fermented in briny water rather than vinegar; look for labels that don’t include vinegar).
You can also boost good bugs by eating more foods that contain prebiotics, substances that stimulate the growth and activity of desirable bacteria already living in your intestine. They help the good bacteria survive or prosper better than other bacteria, Challa says. Pre-biotics, such as the fiber in oatmeal, are soluble fiber, the type that dissolves in water. (Insoluble fiber, like that found in wheat bran, does not dissolve, which is why it contributes bulk to your stool.)