Probiotics: Much Remains to Be Learned


Although some bacteria are harmful, and killing those pathogens is a good thing when you're sick, most bacteria are good.

Microorganisms, or microbes, for short, are everywhere: in the soil, in the water, and even on and in our bodies. Modern hygiene standards have taught us that microbes do bad things. So we arm ourselves with soaps, sprays, and wipes to try to rid germs from our bodies and our homes. When you hear the word bacteria, you probably associate it with being sick. And since the discovery of penicillin in the 1920s, antibiotics designed to kill harmful bacteria, or pathogens, have saved countless lives. Although some bacteria are harmful, and killing those pathogens is a good thing when you’re sick, most bacteria are good. In fact, bacteria play a vital role in supporting nature and life.

A lot has been learned in recent years about the microbiome—the trillions of probiotic bacteria that live inside and on our bodies. However, microbiome research is still in the very early stages. These microbes help our bodies digest and absorb nutrients, manufacture certain vitamins, protect against foodborne pathogens, and rally against intruders, such as influenza and toxic cancer-forming carcinogens. As we are learning, this vast number of microbes, collectively referred to as the human microbiota, have far-reaching effects on our bodies, including genetic control—by stimulating or blocking the expression of certain genes. In fact, recent research has shown that there may even be a link between gut microbiota and obesity, as studies in mice have shown certain microbes can affect behavior and food absorption.

Age, health status, hygiene, and diet can influence your microbe balance. Certain drug therapies, such as antibiotics and colonics, or serious diarrhea, can kill these helpful microbes that inhabit our bodies. When this happens, you want to replenish those beneficial microbes as quickly as possible to protect your health.


Probiotics are foods or supplements that contain live microorganisms that you introduce into your gut in order to obtain some health benefit. Probiotics are said to improve digestive and immune health. They are also touted as potential treatments for conditions such as obesity, dental problems, and diabetes. But, although the evidence is mounting for some possible health benefits, there is still much we don’t know about whether and how the probiotic products now on the shelves can improve health. Most probiotics contain bacteria from the Lactobacillus and Bifidobacterium groups. Within these groups are many different species, and each species has many strains. Other bacteria may also be used as probiotics, and so may yeasts such as Saccharomyces boulardii.


There is a lot we still don’t know about probiotic use: what types of bacteria are best, what is the ideal dosage, what is the optimal length of therapy, and which groups of people will benefit most? Research has shown that taking probiotics may help prevent antibiotic-associated diarrhea and traveler’s diarrhea. They may also shorten the duration of stomach flu symptoms such as diarrhea and other digestive symptoms, but only by about 1 day. Probiotic supplements might also help treat irritable bowel syndrome, and may be useful when used in addition to standard therapy for treating Clostridium difficile (C diff)—associated diarrhea, ulcerative colitis, or bacterial vaginosis.


Most probiotics are sold as dietary supplements or foods, and the FDA doesn’t regulate supplements in the same way it does drugs. For this reason, consumers can’t be sure probiotic supplements contain what’s on the label in terms of the type and number of bacterial cells. Before you start taking or eating probiotics, it is a good idea to discuss them with your health care provider or pharmacist, as probiotics are likely safe for healthy people, but they may cause problems in people who are very ill or who have compromised immune systems. If you decide to take a probiotic supplement that contains bacteria, it is important that you wait at least 2 hours after taking an antibiotic. After taking an oral antifungal medication, wait 2 hours before taking a probiotic that contains yeast.


Prebiotics are foods high in soluble fiber—a nutrient we can’t digest that promotes the growth of helpful bacteria in the gut. Eating foods high in soluble fiber keeps our probiotic bacteria healthy. Think of prebiotics as a healthy meal for the helpful bacteria in your gut. Foods rich in prebiotics include asparagus, Jerusalem artichokes, chicory root, garlic, onions, leeks, bananas, oatmeal, and legumes. And smaller amounts of soluble fiber are found in a wide range of foods, including fruits, vegetables, whole grains, bran, honey, and soybeans. Generally speaking, as long as you’re eating a varied diet that includes fruits, vegetables, legumes, and whole grains, you are probably getting enough prebiotics or soluble fiber to keep your “good bacteria” healthy.


It may be possible to nourish the beneficial bacteria inside us by modifying our diets. We know that dietary fiber serves as food for many of the bacteria that live in our gut and that when bacteria are starved of food, they eat the mucus lining of our large intestines. On the other hand, when the bacteria are well fed, they give off nutrients that nourish the cells that line the intestines. Grains, legumes, fruits, vegetables, and other fiber-rich foods feed the hungry, beneficial bacteria and offer them a fighting chance to crowd out the harmful bacteria. Another way to build a better microbiome may be to eat foods that are naturally full of probiotics, rather than foods that aren’t naturally fermented or cultured. Although natural, probiotic foods may not be as convenient to eat as probiotic supplements, the extra nutrition that foods can offer are a plus. The most natural way to deliver beneficial bacteria to the digestive system is to eat fermented foods such as yogurt, sauerkraut, kombucha, kefir, and kimchi (Sidebar). Other probiotic foods include tempeh, miso soup, some aged cheeses, sourdoughs, and pickled fermentations of turnips, eggplant, cucumbers, onions, squash, and carrots.


Make sure to read product labels and do your research. Choose reputable commercial brands whether you are purchasing probiotic foods or supplements. Not all foods and supplements are created equal, and you don’t want to waste money on products that aren’t actually helping you.

Beth is a clinical pharmacist and medical editor residing in Northern California.


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