The human body harbors as many as 10 times the number of cells of microorganisms, such as bacteria and fungi, as the number of all the cells that make up the physical body combined. This remarkable community of different types of microbes living both in and on our bodies is called the microbiota. Another term, microbiome, is often used interchangeably with “microbiota” (as it will be in this article), though some believe that “microbiome” more properly refers to the collective genetic makeup of the organisms present.

No two people possess the exact same microbiome. Each of us interacts with the diverse mix of microbes that call us home, those healthy for us and those potentially harmful, on a continuous basis. As long as an optimal balance exists between the organisms that are health-promoting and the pathogens among them, we live together in harmony, as well as in ways that are mutually beneficial. For example, the gut microbes living inside us get energy from our bodies and the foods we eat. We depend on those same microbes to break down complex nutrients for us to absorb and for the production of certain vitamins. We need each other. However, when that optimal microbial balance is altered in ways that favor harmful organisms, a disease condition referred to as dysbiosis may occur.

The makeup of an individual’s microbiome develops early in life, but it can change as a result of factors including where and how you were born, where you live and where you have traveled, infections, pharmaceuticals (especially antibiotics) and diet. The microbiome typically returns to baseline under conditions of good health, but even relatively brief alterations can have consequences. This is because the microbiome has a significant impact on the way our body functions, from the way we digest our food and absorb nutrients, to the development and proper functioning of our immune system. A persistent dysbiosis that favors pathogens may contribute to disorders as varied as depression and autoimmunity, autism and obesity, diabetes and even cancer. One of the reasons that my anti-inflammatory diet is so effective is that it supports a healthy microbiome through the ingestion of fermented foods such as sauerkraut, kimchi and yogurt containing live, active cultures, as well as a variety of brightly colored vegetables and fruits and high-fiber foods that provide an energy source (sometimes called prebiotics) for the friendly organisms in our gut. Probiotic products may also have an important role to play in promoting good health.

The World Health Organization (WHO) defines probiotics as live microorganisms that, when administered in adequate quantities, confer a health benefit to the host. Probiotic supplements provide the helpful or “friendly” bacteria (usually Lactobacillus or Bifidobacterium) that normally inhabit our digestive tract. Probiotic therapy is used to increase the number of beneficial bacteria in the digestive tract and optimize microbial balance, and so enhance physical and emotional health — studies show that it may also enhance mood. Probiotics can play an important role in the management of diarrhea, anxiety, irritable bowel syndrome (IBS), vaginal yeast infections, ulcerative colitis and obesity.

I recommend taking probiotic supplements whenever you’re on antibiotics, which can wipe out intestinal bacteria indiscriminately, including those that help keep us healthy. Take a probiotic supplement containing lactobacilli or bifidobacteria twice daily with meals as soon as you start your course of medication and continue for a few days after you finish. Always check the product’s expiration date to make sure the organisms are alive and in good condition, and read the label to be sure the dosage is in the form of billions of colony forming units (CFUs). After you buy, be sure to protect your supply from heat and moisture, and keep it refrigerated if the label so directs.

When I travel in underdeveloped countries, I take probiotics to reduce the risk of traveler’s digestive troubles. You can stay on probiotics indefinitely provided that you do not have a severe immune-deficiency disorder. Taken regularly, they can help restore a healthy microbiome, keep the digestive system in balance and functioning optimally, strengthen immunity and promote optimal health.