Bacteria That's Good for You

The idea of yogurt as a health food lives on, with many of its alleged health benefits attributed to probiotics.
Claims, Benefits: Rebalance the gut's natural flora, reduce diarrhea, help treat ulcerative colitis and IBS, lower blood pressure and cholesterol, treat allergic conditions.

Bottom Line: Consume probiotic cultures in yogurt. But don't look to probiotic supplements as a cure for anything. Some day these bacteria will one day be harnessed as a treatment for disease--but a lot of scientific work still needs to be done.

Gut Reactions

In the early 20th century a Russian scientist observed that Bulgarian peasants who consumed fermented milk products like yogurt lived unusually long lives--many, supposedly, to over 100. Though the longevity of these Bulgarians has since been disputed, the idea of yogurt as a health food lives on, with many of its alleged health benefits attributed to probiotics--microorganisms such as Lactobacillus acidophilus--that are added to milk to ferment it.

Probiotics are also found in other fermented dairy products, some soy products, fruit juices and supplements (capsules, tablets and powders). Do they really provide health benefits?

Probiotic Primer

Our intestines are home to trillions of bacteria, referred to as microflora. Some, of course, can be troublemakers, like the stomach bacterium Helicobacter pylori that causes ulcers. But most are neutral or even friendly, helping to keep "bad" bacteria at bay and performing many other beneficial functions in the body.

For example, they help digest our food, synthesize certain vitamins (K, plus small amounts of some B vitamins), stimulate the immune system and may help prevent carcinogens from forming. Normally, the "good" bacteria prevail; an imbalance between good and bad, on the other hand, is thought to underlie some gastrointestinal illnesses.

The term probiotics (meaning "for life," as opposed to antibiotics) refers to foods and dietary supplements that contain beneficial bacteria, as well as to the organisms themselves. Proponents claim that probiotics confer health benefits when consumed in adequate amounts, primarily by rebalancing the gut's natural flora. There's good evidence that they reduce diarrhea, especially diarrhea that results when antibiotics wipe out the good along with bad bacteria.

Studies also suggest that certain strains can help in ulcerative colitis (an inflammatory bowel disease) and possibly irritable bowel syndrome (IBS). Other potential benefits of probiotics have been claimed--lowering blood pressure and cholesterol, for instance, and treating allergic conditions--but the evidence so far is preliminary, at best.

While probiotics sound promising, it's not certain that ingested bacteria stick to the lining of the intestines and multiply--the only way for them to have any benefit. Some strains may not be able to compete with the bacteria already there. Some don't even survive digestion. Large, double-blind, placebo-controlled studies are still needed to prove the effectiveness and safety of probiotics for different medical conditions, and to find out what the best strains and dose would be (different strains have different physiological effects). It's not known whether probiotics benefit healthy people in any way.

Some Pointers

  • Yogurt and other fermented dairy products (such as kefir) are excellent foods, high in protein and calcium (choose nonfat or low-fat). The "Live & Active Culture" seal from the National Yogurt Association is the best assurance that a certain number of bacteria survived processing--though some may have perished since. Yogurts that are heat-treated after fermentation do not contain live bacteria.

  • If you are lactose-intolerant, you'll probably have less of a problem with yogurt, because the live bacteria will have digested some of the lactose (milk sugar).

  • If you have ulcerative colitis or IBS, talk to your doctor about probiotics. They may be a helpful adjunct treatment.

  • If you are taking antibiotics, there's no harm in eating yogurt or taking probiotics to try to restore a normal balance of bacteria. Check with your doctor or pharmacist first, though, because the calcium in dairy foods can interfere with the absorption of certain antibiotics.

  • Probiotic supplements vary widely in dose and formulation, and they can be expensive. Moreover, there are no regulations to make sure they contain the number of organisms stated on the label--or that the organisms are even alive. Often they contain only a fraction of claimed amounts, or too little to be meaningful, according to independent testing by

  • There is some concern about the safety of some strains, such as Enterococci. If you are severely immune-compromised, have certain bowel problems or are seriously ill in other ways, avoid probiotics unless you have discussed them with your doctor. Probiotics should not be given to premature infants.

What's in Your Yogurt?

Yogurts in the U.S. are fermented with at least Lactobacillus bulgaricus and Streptococcus thermophilus. Some may have additional strains including Lactobacillus acidophilus. New yogurt lines boast of extra probiotic prowess, although there's no convincing evidence that they are any better than regular yogurts. For example, from Dannon:

DanActive is a dairy product fermented with Lactobacillus casei (in addition to the two standard strains in yogurt) and is marketed to strengthen immunity--with little evidence to back up the claims. In one study, for instance, athletes who drank DanActive had higher levels of one immune marker after intense exercise, compared to a control group. But no one knows what practical effect on health this might have.

Activia contains Bifidobacterium animalis (trademarked Bifidus regularis) and makes claims for digestive health. Studies have shown that the bacteria survive in the gut and increase the speed at which food moves through the intestines, which helps with regularity. But how much of a difference it can make is questionable. A high-fiber diet and exercise may be a better way to stay regular.

Reprinted, courtesy of University of California Berkeley. For more articles and information, visit .

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