We tend to think of bacteria as something to avoid. Germophobes beware, but our bodies are literally covered with and filled with bacteria. From our skin to the lining of our GI tract, bacteria are literally part of us. For sure, some bacteria are harmful, but many more play an important role in our health. The balance between the helpful and harmful bacteria seems to be important for health; diseases from eczema to irritable bowel syndrome can result from an imbalance.

The combination of bacteria in our bodies is known as the microbiota, the genes of which are called the microbiome. Researchers study the bacteria themselves (microbiota) and the genes (microbiome) and use both as an indicator of the balance between good and bad bacteria. This is especially relevant in the large intestine, where there has been much research into the role of gut bacteria on health.

The gut bacteria play a critical role in our health from producing essential nutrients to signaling other body systems related to obesity, diabetes, heart disease, cancer and brain function. Just as consuming harmful bacteria can cause intestinal symptoms of food poisoning, thriving colonies of beneficial bacteria can improve the health of the intestine and the whole body. You're right to expect that what you eat can influence your gut bacteria, either positively or negatively. In many ways the gut microbiota is also a missing link between what we eat and health. The food we consume can influence our health through the nutrients themselves and the way those nutrients affect the gut bacteria.

There is much interest in altering the gut bacteria through food and supplements. Probiotics are strains of bacteria that when eaten will introduce healthy bacteria in the intestine. Bacteria in yogurt and fermented foods like sauerkraut are two examples of foods that may have this effect. Supplements containing beneficial bacteria are also available. Prebiotics are foods containing certain starches and fiber that promote the growth of healthy bacteria. Examples include high-fiber foods like vegetables, fruits, legumes, whole grains, nuts and seeds.

Much of the evidence that probiotics and prebiotics can alter the gut microbiota in a positive way come from rodent research. There are comparatively few studies in humans, but there is some evidence that consuming more probiotic and prebiotic foods and supplements is beneficial. However, there is still much uncertainty about the type, dose and specific effects of these foods and supplements on gut bacteria and health in general. The research so far does not fully support the theory that you can eat your way to a healthy gut microbiome, but it probably does help.

Recent research suggests that exercise also has a positive effect on the intestinal microbiota. Exercise can cause changes in the specific bacteria as well as their metabolic activity. This could be due to many physiological changes that occur during exercise including body temperature, blood flow, nervous system activity, energy use and alterations to the intestinal lining. These changes can reduce inflammation and oxidative stress, which may have benefits on the brain, fat and muscle tissue, and other organs. This may protect against colon cancer, inflammatory bowel disease (IBD), depression, anxiety, obesity and heart disease.

The influence of exercise on the gut bacteria has far-reaching effects that are an important part of the broad health benefits of exercise. And unlike some supplements designed to improve gut health, exercise has many other benefits beyond the intestine and has been shown to prevent and treat almost every chronic disease. Thats something no probiotic supplement or single prebiotic food can match!

Brian Parr, Ph.D., is an associate professor in the Department of Exercise and Sports Science at USC Aiken where he teaches courses in exercise physiology, nutrition and health behavior. You can learn more about this and other health and fitness topics at http://drparrsays.com or on Twitter @drparrsays.

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HEALTH AND FITNESS: Exercise and the gut microbiome - Aiken Standard