From the bacterial point of view, the human intestine is the promised land. The gut is warm, moist, and full of good food. It’s also extremely crowded. A cubic centimeter of prime real estate in the colon can hold 100 billion bacteria — nearly 20 times the entire human population of earth.

A few hundred billion bacteria may seem like plenty, but some people might benefit from even more. Probiotics, remedies containing many millions of live “good” bacteria, have become hot sellers in health food stores across the country. Some people get their bacteria in capsules; others prefer live-culture yogurts. The basic goal is the same: In with the good bugs, out with the bad.

Should you be taking regular doses of bacteria? The answer isn’t quite as simple as marketers would like you to believe. Probiotics clearly have potential. Recent studies suggest they may help fight antibiotic-induced diarrhea and prevent diarrhea in some people, especially children. There is also encouraging evidence that they may help prevent eczema in children, fight recurrent urinary tract infections, and treat irritable bowel syndrome. They may also boost the immune system and even help slow the development of some types of cancer, according to animal studies discussed in the American Journal of Clinical Nutrition. Still, many questions remain. Here’s a look at the promise, and the pitfalls, of bacterial medicine.

Good bugs, bad bugs

The typical intestine holds hundreds of different species of bacteria and other assorted microbes. But unless you’re studying for your microbiology degree, you only need to know about a few of them.

Bacteria belonging to the genus Lactobacillus are some of the good guys. These organisms attach to the lining of the intestine and produce compounds that kill disease-causing germs. Other helpful inhabitants include Bifidobacterium, which are especially abundant in infants, and saccharomyces boulardii, a yeast that constantly wages war on harmful bacteria.

There are plenty of germs to keep the good guys busy. Salmonella, campylobacter, and many other nasty bugs can invade the digestive system through tainted food and water. And if conditions are right, harmful bacteria that naturally inhabit the intestines can begin to grow out of control. For instance, antibiotics — drugs that inevitably disrupt the natural balance of bacteria in the gut — often lead to a population boom of clostridium difficile. As a result, many people suffer severe diarrhea as a side effect of the medications.

Keeping your balance

If you don’t have the right type of bacteria in the right numbers, your whole body can suffer. And according to Jon Vanderhoof, MD, director of the Department of Pediatric Gastroenterology and Nutrition at the University of Nebraska Medical Center, modern living often tips the scales in the wrong direction.

In the old days, people ate more bacteria-rich fermented foods (such as yogurt, buttermilk, and sauerkraut), according to Vanderhoof, and they encountered many more germs in their day-to-day life. Today, the supply has dwindled. Since our environment is more sterile, we don’t get exposed to as many healthy bacteria, Vanderhoof says. “About the only things we ever ingest are pathogens.”

Allergy protection?

A shortage of good germs may be wreaking havoc on our immune systems, Vanderhoof says. A steady supply of bacteria — especially early in life — helps “wake up” the immune system, giving it the strength to fend off harmful intruders. And if the immune system never gets that call to action, it just might lose its focus. Instead of fighting germs, it might start fighting pollen and cat dander and other harmless substances. In other words, a shortage of bacteria may set the stage for allergies.

To illustrate, Vanderhoof points to Finland and Estonia, neighboring countries in Northern Europe. Allergies are extremely common in squeaky-clean Finland, but they are rare in impoverished Estonia. Short of spreading poverty all over the world, probiotics may be the best way to stem the modern epidemic of allergies, Vanderhoof says. “Maybe we should be using probiotics to put us in a germ-fighting mode, not an allergic mode,” he says.

A study published in The Lancet adds support to his theory. (Appropriately enough, the study was conducted in Finland.) Researchers gave capsules of Lactobacillus to 64 pregnant women with a family history of eczema, a skin disorder that causes severe itching and redness. The mothers continued to take the capsules for six months after the babies were born. Babies who weren’t breastfed received the bacteria directly.

When the babies turned two, 15 of them (23 percent) had eczema. That may not seem impressive, but consider this: Eczema was twice as common in a control group of kids who didn’t receive the bacterial boost.

Vanderhoof also tells an anecdote about putting the theory to the test in his own family. His first grandson was born with severe allergies. When his daughter became pregnant again, he encouraged her to take Lactobacillus capsules in the weeks before delivery. Two years later, his granddaughter still harbors a healthy colony of Lactobacillus. She is also completely free of allergies.

Germs to the rescue

According to Vanderhoof, the probiotic remedy for allergies may only work in infancy, when the immune system is most receptive. For the rest of us, the main value of probiotics may be keeping bad germs in their place.

Two studies published in the American Journal of Gastroenterology found that combining S. boulardii with antibiotics cut the risk of diarrhea roughly in half. In a European study, live cultures of Lactobacillus significantly shortened the hospital stays of 287 children with diarrhea caused by rotavirus. Other studies have found that Bifidobacterium can help prevent diarrhea in hospitalized children and that Lactobacillus can cut the risk of travelers’ diarrhea.

According to the National Center for Complementary and Alternative Medicine (NCCAM), probiotics have been shown to reduce the recurrence of bladder cancer. It’s also possible that the organisms in probiotics give the immune system extra strength to kill cancer cells.

Probiotics are generally safe, though NCAAM says further studies are needed to be sure probiotics are safe for young children, the elderly, and people with compromised immune systems. Some people may experience mild side effects such as gas or bloating. There is a remote chance that bacteria could cause an infection in the blood, especially in people with extremely weak immune systems. It’s a good idea to talk to your doctor before trying a probiotic, just to be on the safe side.

Buyer beware

None of this means it’s time to start ingesting every germ on the market. Like many other dietary supplements and natural remedies, store-bought probiotics don’t always live up to the claims on their packages. A study of probiotics sold in England found that only two out of 13 brands actually contained the advertised bacteria in the advertised amounts. One brand that claimed to provide 250 million Bifidobacterium per capsule fell short of the mark by about 250 million cells.

You also shouldn’t depend on yogurt, without reading the label carefully. The strains of Acidophilus and other bacteria found in most yogurt are custom-made for cows, and they usually can’t form colonies in the human intestinal tract. “If they don’t form colonies, they don’t work,” Vanderhoof says. Dannon has come out with a yogurt called Activia, which contains a strain of Bifidobacterium. The company claims that eating Activia every day for two weeks can help regulate your digestive system. Of course, any yogurt is a nutritious snack that’s easy on the stomach. If you’re suffering from diarrhea or an upset stomach, a few extra servings certainly wouldn’t hurt.

Getting the best from your bugs

If you choose carefully, probiotics can give your body a big boost, says Gary Elmer, PhD, a professor of medicinal chemistry at the University of Washington. In fact, Elmer believes many more people should be giving them a try. “They won’t cause any harm, and they might do a lot of good.”

Elmer recommends sticking to proven strains of bacteria distributed by reputable companies. If your child develops diarrhea, consult with your doctor about the wisdom of giving him Primadophilus (containing L. reuteri), Probiotica (L. reuteri), or Culturelle (containing L. rhamnosus). If you have to take antibiotics and want to avoid diarrhea, Elmer suggests trying Florastor (S. boulardii). If you’re taking a trip to an area with poor sanitation, a few doses of Culterelle just might help you avoid frequent trips to the bathroom. Other bacteria and other brands may be helpful, but they remain unproven, he says.

Perhaps none of these scenarios apply to you. Perhaps you’re an adult who simply wants to feel better. Again, Elmer says, probiotics might be worth a try. Like a bowl of soup, a few million good bacteria couldn’t hurt.


National Center for Complementary and Alternative Medicine. An Introduction to Probiotics. August 2008.

Elmer GW. Probiotics: Living drugs. American Journal of Health-System Pharmacists, Vol. 58: 1101-1109.

Meydani SN and WK Ha. Immunologic effects of yogurt. American Journal of Clinical Nutrition. April 2000. 71:861-872.

Journal of the American Medical Association (News and Perspectives). A bit of culture in children: Probiotics may improve health and fight disease. Sep 20, 2000.

Vanderhoof JA. Probiotics: Future directions. American Journal of Clinical Nutrition. June 2001. 73(suppl): 1152S-1155S.

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