Even for those without an urgent problem, probiotics can help with overall digestive management. Challa argues in his book, Probiotics For Dummies, that good bacteria help "crowd out" bad bacteria. That's because the intestine is lined with adherence sites where bacteria latches on. If the sites are populated with good-for-you microbes, there's no place for a harmful bacterium to latch on.
How can something as small as a microscopic organism be so important for health? The reason is that there is not just one microbe, nor a handful; there are approximately 1 trillion microbes per gram of feces. Microbes within you are found on your mucous membranes, spanning from your mouth to your anus, from your nasal passages to your lungs, in your urinary tract, and even on your eyes. In fact, in your digestive tract alone, it is calculated that for every cell of yours that is human, there are an equal number of bacterial cells.
There are two main types of probiotics; the first is the live cultures I describe above, like the strains of Lactobacillus and Bifidobacterium. You might have heard some naysaying about this kind of probiotic—the typical argument against them is that the classic form of live cultures is destroyed by the acidic environment in the stomach. To get around this, quality probiotics are made with an acid-resistant capsule so that they don’t get immediately broken down. (Which means you don’t have to take the probiotics with food, although I normally do. I’ll sometimes break the capsule and mix it into a smoothie, or use the powder form. You might lose a bit of potency but it’s not significant.)

CFU: This is the number of "colony forming units" present in each dose, which are measured in the billions. And while more isn't always better, "you want at least 20 to 50 billion CFU," says Dr. Nazareth. Just for reference, a very high dose is 400 CFU, which most experts agree is not necessary unless your health care practitioner specifically recommends this for you. It's also important to check for the guaranteed CFU upon expiration, which should be listed clearly. "Some products only guarantee the CFU number at the time of manufacturing, therefore will be less potent by the time the product reaches your home," she says.
The classic examples of probiotics are yogurt and kefir, which are great for a lot of people, though not if you have a dairy sensitivity. There a lot of yogurt and kefir alternatives, from water kefir and almond yogurt, to coconut yogurt, coconut kefir, and so on. Look at ingredients when you’re shopping for food like yogurt—you want to avoid sugar-filled products. I like plain coconut yogurt with fruit and little stevia on it.
Better Health Review ranks Ultimate Flora as the most effective probiotic supplement. It contains 30 billion active bifidobacteria for colon health, and 20 billion lactobacilli and lactococcus cultures for the small intestine. According to Better Health Review, it contains all natural ingredients. It earns a perfect 5 score from Better Health Review, and the magazine “Vitamin Retailer” voted it best two years in a row. 
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