“A probiotic is any substance containing live organisms that, when ingested, have a beneficial effect on the host by altering the body’s intestinal microflora.”  Probiotics are often referred to as the “good” bacteria and can be found in yogurt, kefirs, and in pill-form as dietary supplements. The “good” bacteria can include Lactobacillus reuteri, Lactobacillus rhamnosus, and Bifidus regularis. 
The theory behind probiotics is, “certain strains of these living organisms – or good bacteria—can displace bad bacteria in the gut.”1 One trial dealing with the popular Activia yogurt split healthy volunteers into two groups: one ate Activia and the other ate an inactive form of Activia product with no love bacteria. At the end of the study, the volunteers who ate the Activia with live bacteria experienced a 21% decrease in colon transit time (meaning food passed more quickly out of their bodies).1
According to Dr. Gary Huffnagle: “In the digestive tract the bacteria help to regulate and restore peristalsis, the rhythmic motion of he intestine that pushes digested food through…Doesn’t matter if you are constipated or the opposite…these bacteria can help make you regular.”2
In addition to aiding in regularity, the “good” bacteria can also battle numerous forms of allergies, irritable bowel, and pediatric diarrhea.1,2 In a recent study, researchers gave Lactobacillus GG, sold under the brand name Culturelle or VSL-3, to pregnant women with a history of allergies and then to their infants. The study revealed babies who received Lactobacillus GG developed a significantly lower rate of allergic eczema than the control group that did not take the product.1 However, in other studies in children with well-managed Crohn’s disease, probiotics did not reduce gastrointestinal flare-ups.1
Currently, because probiotics are categorized as dietary supplements, the Food and Drug Administration (FDA) does not approve them.1 In addition, there are some people who should not take probiotics. According to Dr. Gupta, those with weakened immune systems and those who are critically ill should not ingest foods with live bacteria.2 Furthermore, probiotics can take some time to adjust to. If one suddenly began to ingest large amounts of probiotic products, there is a possibility of developing uncomfortable bloating.2
As Dr. Huffnagle reports: “You have just started a civil war in your intestines between good bacteria and bad bacteria….Fortunately the war is usually over in one to two weeks and the good guys win.”
Dr. Gupta suggests plain yogurt remains the best product for added bacteria because it has three things the bugs absolutely love: lactose, fat, and water. However, with more than $100 million in sales in Activia’s first year in the U.S. alone, the “good” bacteria idea seems to be paying off.2 Due to successful sales of Activia, other companies are beginning to market probiotic yogurt drinks, fortified beverages, and chocolate bars.
I am not yet sold on the idea of probiotics. Personally, I prefer to stick with plain old yogurt instead of the super infused bacteria yogurt.