Apr. 09, 2014

Yogurt, Breakfast of Champions?

by Jordan Davidson

Click to enlarge images
What would you pay for a tasty treat that’s satisfying and could potentially keep weight down, while also improving how parts of your brain work? How about a few bucks a day? The snack is probiotic yogurt—the kind with active bacterial cultures. A growing body of mouse and human studies over the past few years suggests that the microbes found in these dairy products could contribute to improved health.
Take Lactobacillus reuteri, a bacterium found in yogurt. In a study published last summer in PLOS One, researchers fed mice chow that mimicked a fast-food diet—think, high fat, low fiber. The mice fattened up, lost energy, and got sick. The researchers then added probiotic bacteria to the mice’s diet, delivered either via a yogurt meal or as a supplement containing purified L. reuteri added to drinking water. The serving initiated an immune response involving anti-inflammatory T-regulatory cells, which enable the body to healthily use energy and metabolize effectively.
The bacteria were so effective that mice that consumed probiotics in addition to a fast food diet were significantly more slender than mice eating a control meal. The probiotic-fed mice also had more energy and fewer fat-related diseases such as organ failure, according to Susan Erdman, assistant director in the Division of Comparative Medicine at MIT, and the senior author of the study.
While this study hasn’t yet been replicated in humans, the results suggest that “microbial therapies have huge public health potential,” says Erdman. “Probiotics may protect against obesity even with occasional dietary indiscretions.” Indeed, a study appearing in The New England Journal of Medicine in 2011, which investigated weight gain in three groups of people who have been tracked by scientists for decades, found that yogurt (among other foods) was associated with less weight gain in each group.
The probiotics found in yogurt seem to have positive effects beyond weight control, too—at least where mice are concerned. In another paper published in PLOS One in January 2013, Erdman and colleagues found that older female mice that ate probiotic yogurt or took a probiotic supplement experienced an immune response that improved the quality of their skin and hair as it grew. Vaginal acidity levels became more acidic, too, corresponding to levels associated with peak fertility. Meanwhile, older male mice fed probiotics didn’t experience the usual decrease in testicle size, which generally happens as mice age.
“The probiotics induce a healthful immune balance and regulate hormones,” Erdman says. “This combination stimulates youth and peak fitness, which is inherently appealing when looking to mate.”
While Erdman stresses that it’s the probiotic bacteria delivering the effect, not the yogurt, the mice seemed to enjoy the dairy treat. “Mice are hilarious when you give them yogurt,” she says. “You should see how they scamper. They can’t contain their enthusiasm.”
The mice aren’t alone—Erdman enjoys her yogurt, too. Anecdotally, she says she’s noticed the health effects. “When I started eating lots of probiotics, it changed my thought process,” she says. “I thought more clearly. I felt better and happier.”
At least one study seems to support her observation. Reporting last summer in Gastroenterology, researchers detected a connection between bacteria found in yogurt and how the brain functions. The team compared women who ate probiotic yogurt daily with women who ate dairy without live, active cultures and with women whose diet was untouched. The study participants underwent several brain scans before and after the diet changes.
In response to pictures of angry or fearful faces, women who ate probiotic yogurt daily showed decreased activity across a wide network of the brain that controls responses to sensation, threat, and emotion, while women in the other groups showed increased activity or no change. The women who consumed yogurt “see the threatening images, but the brain stays relaxed. It isn’t preparing to respond to that threat in the same way as the control group,” says Kirsten Tillisch, an associate professor of medicine in the digestive diseases division at UCLA and the lead author of the study. She adds that more research is needed to make that conclusion definitive.
Yogurt’s active cultures may have been responsible for changing the women’s resting brain function as well. The researchers measured brain activity in the women as they lay quietly with their eyes closed. They found that in those who ate probiotic yogurt, a region in the brain stem interacted more with brain regions associated with cognition and less with a network of regions associated with emotion and sensation. Tillisch explains the effect this way: “In a resting state, they’re devoting more of their energy to higher-order thinking rather than the reflexive brain,” she says, “There’s clearly a connection between the microbes and our brain functioning.”
The mechanisms for how probiotic yogurt impacts health is an area of active research, according to Lita Proctor, the director of the Human Microbiome Project at the National Institutes of Health. Some of its apparent benefits could stem from the way it interacts with a mammal's gut microbiome—that is, the array of bacteria that already lives in the lower digestive track and comprises more than 90 percent of an adult human's cells. Research has shown that these microbes influence various aspects of health, including metabolism and immune function, according to a report in the Annals of the New York Academy of Sciences
To gain any potential rewards of probiotic yogurt, however, it’s not enough to eat a serving here and there—spooning the stuff should become habitual. “It requires consistency to maintain the milieu of the bacteria and to reap the benefits,” says Tillisch. 
Erdman echoes this sentiment. “You wouldn’t go for a jog once and say you’re in good shape,” she says. “The same goes for your gut.” What’s important, she says, is constant attention to a healthy diet that supplies and supports beneficial bacteria.
Further, while the benefits of yogurt might make a probiotic binge sound like a good idea, “the vast majority of probiotics do absolutely nothing,” says Ted Dinan, a professor of psychiatry at University College Cork in Ireland, who is part of a team researching how probiotics could be used to treat depression. 
So, the next time you're out shopping for snacks, go with your gut.
*This article was updated on April 10, 2014 to reflect this correction: "Stimulates" should have been "simulates" in the following quote from Susan Erdman: "This combination simulates youth and peak fitness, which is inherently appealing when looking to mate.”
About Jordan Davidson

Jordan Davidson is a freelance writer based in New York.

The views expressed are those of the author and are not necessarily those of Science Friday.
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