Even if some of the bacteria in a probiotic managed to survive and propagate in the intestine, there would likely be far too few of them to dramatically alter the overall composition of one's internal ecosystem. Whereas the human gut contains tens of trillions of bacteria, there are only between 100 million and a few hundred billion bacteria in a typical serving of yogurt or a microbe-filled pill. Last year a team of scientists at the University of Copenhagen published a review of seven randomized, placebo-controlled trials (the most scientifically rigorous types of studies researchers know how to conduct) investigating whether probiotic supplements—including biscuits, milk-based drinks and capsules—change the diversity of bacteria in fecal samples. Only one study—of 34 healthy volunteers—found a statistically significant change, and there was no indication that it provided a clinical benefit. “A probiotic is still just a drop in a bucket,” says Shira Doron, an infectious disease expert at Tufts Medical Center. “The gut always has orders of magnitude more microbes.”
However, it is not just digestive woes that probiotics can help address. A clinical case series followed 300 patients who took a probiotic mixture of L. acidophilus and L. Bulgaricus. They documented that 80% of acne patients had some degree of clinical improvement, particularly effective in inflammatory acne. Later, an Italian study involving 40 patients found L. Acidophilus and B. Bifidum supplementation produced better clinical outcomes in acne as well as better tolerance and compliance with antibiotics [2].
Helicobacter pylori (H. pylori) is a bacteria that causes chronic inflammation (gastritis) of the inner lining of the stomach, and also is the most common cause of ulcers worldwide. About 50% of people in the world carries or is infected with H. pylori. Common symptoms of H. pylori infection are occasional abdominal discomfort, bloating, belching or burping, and nausea and vomiting. H. pylori infection is difficult to erdicate, and treatment is with two or more antibiotics.
Bacillus is an interesting genus because these microbes have the ability to form endospores, tough outer coatings, when conditions are not suitable for them to flourish. There are five species of probiotic Bacillus: clausii, coagulans, indicus, licheniformis, and subtilis. Not every species of Bacillus is probiotic. Some Bacillus species are usually pathogens. Bacillus may normally be found in the GI tract, but they generally do not take up residence for long and will pass through and be eliminated if not replenished. Bacillus are common food spoilage organisms and are also found in probiotic supplements and in soil, air, and water.
We have to give a nod to the most famous probiotic food: yogurt. Whether you love Greek or regular, low-fat or full-fat, look for the phrase "live active cultures" on the label. And although choosing a plain yogurt has less added sugar than the flavored kinds, Tallmadge gives you the okay to choose a fruit-infused flavor if that's the only way you'll eat it. Just be sure to aim for fewer than 15 grams of the sweet stuff per serving; sugar can feed the bad bugs in your gut.
While taking a daily probiotic supplement may seem like an easy answer to cure common gut ailments, it’s always best to try for a food first approach, since you can get probiotics from the foods you eat. Probiotics can be found in foods such as yogurt, cheese, miso, sauerkraut, and kimchi. But, adding a supplement into the mix if you haven’t achieved the desired effect through diet alone can be effective.
Some companies have been around for years, and you may know their names. Those that have made probiotics for a while likely have tested and studied them over and over. It's smarter to choose a product from them over one from a maker you don't know. Check a third-party certifier (like ConsumerLab or the USP) to see if they have tested the product and found that it’s safe and reliable. If you're in doubt, ask your doctor.
As with other types of supplements, scientists are still discovering the full potential of probiotics. However, when taken regularly, it is believed that they help support digestive health by helping maintain the balance of beneficial and non-beneficial bacteria in your digestive tract. Having a natural balance of good bacteria in the digestive tract can help defend against occasional digestive issues. In addition, probiotics play an important role in supporting immune health, since 70% of the body's immune system is found in the digestive tract.∗ 
×