The human gut is full of trillions of little bugs. But they're not, for the most part, the pathogens that make you sick; their purpose is actually to help keep you well. We've known for a while that the good bacteria inhabiting the gut (which includes the stomach and intestines) aid in digestion and help boost the immune system by identifying potentially dangerous foreign invaders. But until recently, this was about all we knew. Now we're able to sequence thousands of genes to get a detailed, high-def look at the gut microbiome—and the findings are astounding. The bacteria aren't just linked to digestive health; they're connected to conditions throughout the body, from the heart to the brain.

Heart Disease

One recent study found that people who lacked certain types of bacteria in their digestive tract had a higher BMI and elevated triglyceride levels, two major risk factors for cardiovascular disease. In fact, the microbiome accounted for nearly 5 percent of the differences in subjects' body fat and 6 percent of the differences in their triglycerides. Translation: Bacteria could partially explain why some of us are heavier than others and run a greater risk of heart trouble. What's more, one study found that when people with high cholesterol were given a type of bacteria called Lactobacillus reuteri, their bad (LDL) cholesterol level significantly decreased.

Mental Health

Studies have found associations between gut bacteria and mental disorders like anxiety, depression and schizophrenia. This research is still in the early stages, but scientists speculate that the microbiome may cause the release of neuroactive substances that affect brain function and fundamental behavior patterns like social interaction and stress management—two things that can go awry in mentally ill patients.

Autoimmune Conditions

Recent research suggests that some chronic gastrointestinal ailments, such as Crohn's disease and ulcerative colitis, may be triggered, at least in part, when the immune system is overstimulated by a plethora of certain bacteria within the G.I. tract. One report, for instance, found that individuals with irritable bowel disease (IBD) had less of the bacteria Bacteroidetes and Lachnospiracea but much more Proteobacteria and Bacillus compared with an IBD-free control group.

What's Next?

Microbiome research is a new frontier in medicine. While studies have shown that changing the microbiome in an animal can lead to changes in its health, the data for humans are a bit more ambiguous. Is an abnormal microbiome a result of having a mental disorder? Or is it causing the mental disorder? No one has the answers to these questions yet, but there's still good reason to consume probiotics (like those found in yogurt), even though we are far from any kind of targeted treatment. I'm hopeful that one day soon, scientists will be able to link bacterial imbalances to specific conditions. How great would it be to get a prescription for sauerkraut (a natural probiotic) to treat your high cholesterol?

Q: Do I Need a Prebiotic?

A: Probiotics are live bacteria; prebiotics are the fermented dietary fiber that probiotics feed on. One benefit to consuming prebiotics is that they're resistant to stomach acid and bile, while some probiotics die when they come in contact with digestive juices. Two types of prebiotics that have been shown to increase probiotic growth are the space-age-sounding galactooligosaccharides (GOS) and fructooligosaccharides (FOS). Sources of GOS and FOS include oats, legumes, garlic, onions and bananas. My recommendation: Enjoy your yogurt with a side of prebiotics to keep your good bugs thriving.

Mehmet Oz, MD, is the host of The Dr. Oz Show (weekdays; check local listings).


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