"This suggests that probiotics should not be universally given as a 'one-size-fits-all' supplement," study co-senior author Eran Elinav, an immunologist at the Weizmann Institute of Science in Israel, said in a statement. However, it may be possible to tailor probiotic treatments to the individual, based on the types of microbes already in his or her gut, as well as other factors, so that he or she gets the most benefit from probiotics, the researchers said.

Yogurt is a well-known food source of probiotics, beneficial bacteria that promote health. Certain strains of bacteria in yogurt have ß-D-galactosidase, which is an enzyme that helps break down lactose in dairy products into the sugars glucose and galactose. A lack of this enzyme causes lactose malabsorption. People who eat fresh yogurt containing live and active cultures digest lactose better than those who eat pasteurized yogurt. Yogurt is also rich in minerals like magnesium, phosphorous, potassium, and calcium, which are important for building and maintaining healthy bones.. The USDA MyPlate recommends that adults consume 3 cups of calcium-rich dairy products, including milk, cheese, and yogurt, per day. What counts as a cup of dairy? One cup of milk or yogurt, 2 ounces of processed cheese, and 1 ½ ounces of natural cheese all count as a cup of dairy. Lactobacillus bulgaricus is a probiotic organism that is often found in yogurt.
The manipulation of the gut microbiota is complex and may cause bacteria-host interactions.[7] Though probiotics are considered safe, some have concerns about their safety in certain cases.[7][40] Some people, such as those with immunodeficiency, short bowel syndrome, central venous catheters, cardiac valve disease and premature infants, may be at higher risk for adverse events.[5] In severely ill people with inflammatory bowel disease there is a risk of the passage of viable bacteria from the gastrointestinal tract to the internal organs (bacterial translocation) as a consequence of bacteremia, which can cause adverse health consequences.[7] Rarely, consumption of probiotics by children with lowered immune system function or who are already critically ill may result in bacteremia or fungemia (i.e., bacteria or fungi in the blood), which can lead to sepsis, a potentially fatal disease.[6]

Quality matters for any supplement, and that goes triple for probiotics. Many commercial brands lack the technology to identify specific strains and how much of that strain each dose contains. That could mean you get an ineffective or potentially harmful dose. It's a great sign if the company is using strains that have been used specifically in clinical trials at a dose similar to or the same as that used in the study. This is one of the only ways to guarantee a probiotic's clinical effectiveness.
Probiotics may also be of use in maintaining urogenital health. Like the intestinal tract, the vagina is a finely balanced ecosystem. The dominant Lactobacilli strains normally make it too acidic for harmful microorganisms to survive. But the system can be thrown out of balance by a number of factors, including antibiotics, spermicides, and birth control pills. Probiotic treatment that restores the balance of microflora may be helpful for such common female urogenital problems as bacterial vaginosis, yeast infection, and urinary tract infection.
If you're healthy and want to stay that way... Shoot for 50 to 100 billion CFUs of a combo of lactobcillus and bifidobacterium. Starting with a large amount of CFUs will either keep you riding high (by supporting immunity) or trigger small but yucky reactions, like gas or nausea. If you notice those, scale back to 50 billion, then 20 bill, until you feel like your usual (but better) self.
Diarrhea is a change is the frequency and looseness of bowel movements. Symptoms associated with diarrhea are cramping, abdominal pain, and the sensation of rectal urgency. Causes of diarrhea include viral, bacterial, or parasite infection, gastroenteritis, food poisoning, and drugs. Absorbents and anti-motility medications are used to treat diarrhea.
Probiotics are live microorganisms that are thought to have health benefits, as the National Institutes of Health (NIH) reports. These bacteria and yeast are believed to help populate our guts with beneficial microbes, according to Mayo Clinic, and can be found in fermented or unpasteurized foods including yogurt, kefir, sauerkraut, and kimchi, as well as, yes, supplements.
Antibiotics are a common treatment for children, with 11% to 40% of antibiotic-treated children developing diarrhea.[13] Antibiotic-associated diarrhea (AAD) results from an imbalance in the colonic microbiota caused by antibiotic therapy.[13] These microbial community alterations result in changes in carbohydrate metabolism, with decreased short-chain fatty acid absorption and osmotic diarrhea as a result. A 2015 Cochrane review concluded that a protective effect of some probiotics existed for AAD in children.[13] In adults, some probiotics showed a beneficial role in reducing the occurrence of AAD and treating Clostridium difficile disease.[14]
Can you take one probiotic for digestive health and a different one for vaginal health? “Unless recommended otherwise by a healthcare professional, I would recommend staggering intake within a day,” says Anthony Thomas, PhD, director of scientific affairs at Jarrow Formulas. In other words, take one probiotic with breakfast and the other at lunchtime.
Since the effects of individual bacteria strains vary, the first thing to consider when choosing a probiotic supplement is the reason you are taking it. Certain strains, for example, may help with weight loss, lower cholesterol or reduce allergy symptoms, while others have been shown to help with digestive issues, such as diarrhea from antibiotics and irritable bowel syndrome. The uses and evidence for various strains are summarized in a reference table in the Probiotic Supplements Review (be aware that certain strains should be avoided by people with milk allergies or people taking certain medications). 

Prebiotics are non-digestible food components that promote the growth of healthful bacteria in your gut. In essence, they are "good" bacteria promoters. In addition to improving digestive health, prebiotics can also enhance calcium absorption. Prebiotics are components of nondigestible fibers and are found in many plant foods. Rich sources of prebiotics include garlic, onion, leeks, asparagus, dandelion greens, and sunchokes. Prebiotics and probiotics work synergistically to optimize gut health. Hench, meals or products that combine these together have a symbiotic effect.
The prebiotic comes before and helps the probiotic, and then the two can combine to have a synergistic effect, known as synbiotics. A prebiotic is actually a nondigestible carbohydrate that acts as food for the probiotics and bacteria in your gut. The definition of the effect of prebiotics is the selective stimulation of growth and/or activity(ies) of one or a limited number of microbial genus(era)/species in the gut microbiota that confer(s) health benefits to the host. The health benefits have been suggested to include acting as a remedy for gastrointestinal (GI) complications such as enteritis, constipation, and irritable bowel disease; prevention and treatment of various cancers; decreasing allergic inflammation; treatment of nonalcoholic fatty liver disease (NAFLD), and fighting immune deficiency diseases. There has also been research showing that the dietary intake of particular food products with a prebiotic effect has been shown, especially in adolescents, but also tentatively in postmenopausal women, to increase calcium absorption as well as bone calcium accretion and bone mineral density. The benefits for obesity and type 2 diabetes are growing as recent data, both from experimental models and from human studies, have shown particular food products with prebiotics have influences on energy homeostasis, satiety regulation, and body weight gain.