People are ecosystems. A healthy adult can harbor about 100 trillion bacteria in his gut alone, which is 10 times as many as the number of cells in his body. In exchange for raw materials and shelter, the body’s commensal bacteria or “microbiome” feed and protect their hosts. The “normal” microbiome digests dietary fiber, generating short fatty acids that serve as fuel for certain cells’ metabolic needs, or are also stored as fat.

In addition to Irritable Bowel Syndrome (IBS), Inflammatory Bowel Disease (IBD), Antibiotic-Associated Diarrhea, and Infectious Diarrhea, an altered microbiome has also been associated to Atherosclerotic Heart Disease, Obesity, Diabetes, Metabolic Syndrome, Non-Alcoholic Steato-Hepatitis and various presumably “auto-immune” diseases such as Type 1 Diabetes, Eczema, Multiple Sclerosis and even Autism. Modifying microbiomes with antibiotics in specially bred mice predisposed to hardening of the arteries significantly reduces their Atherosclerosis. In Multiple Sclerosis, researchers have shown in mice that gut bacteria trigger the reaction that causes the immune system to turn against certain nerve cells and strip away their insulation in precisely the way that leads to multiple sclerosis.

If gut bacteria are making you ill, can swapping them make you healthy? The yogurt industry has been answering this question for many years. Indeed probiotics – which are live micro-organisms that when administered in adequate amounts, confer a health benefit to the host – are found in yogurt. Although it is commonly recommended as a source of probiotics, not all of the live cultures contained in yogurt survive well in an acidic environment, nor do they colonize the microbiome efficiently. Some yogurt preparations in the United States are pasteurized, which kills the bacteria. Furthermore, the residual lactose contained in yogurt can increase symptoms in patients with lactose intolerance, including those that develop secondary lactose intolerance following an episode of acute gastroenteritis.

Since yogurts are limited in the range and amount of bacteria they can transmit, different concentrated probiotic formulations have been developed and studied scientifically. Some of the most commonly available include: VSL#3, Align, Culturelle, DanActive, Mutaflor and Florastor. Unfortunately, very few studies have hinted that probiotic pills may improve your health, and scientists claim that there is not enough proof and more research is needed. Hence, these pills should not be taken unless recommended by your physician.

However, there is no harm in eating yogurt products that have “active cultures” which have probiotics in them. A low-fat yogurt can always be part of a healthy diet. The downside is that probiotics are not regulated by the FDA and therefore the manufacturers do not have to prove that the ingredients listed on the label are actually in the bottle. Furthermore, probiotics are expensive and not covered by insurance (except for VSL#3 DS in “pouchitis”) and there is a small chance that they can cause infections in people with weak immune systems.