Bugs in balance: The probiotic approach

The good bacteria in the human gut play a huge role in maintaining health. Sometimes they need a little help.

By Susan J. Landers — Posted Oct. 3, 2005

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When treated with an antibiotic for recurring infections, a patient of Robert Bonakdar, MD, a family physician in San Diego, invariably confronted a round of debilitating stomach problems -- bloating, upsets and diarrhea. His conundrum raised the possibility that the cure really was worse than the disease.

But all that changed when the patient also took an over-the-counter product packed with strains of good bacteria that normally populate the gut. "In this case, the patient was able to take the antibiotic and not have the diarrhea," said Dr. Bonakdar, who practices at the Scripps Center for Integrative Medicine and also heads an annual conference there. The conference brings in experts to help physicians sort through the "good, the bad and the ugly" of the booming supplement field, he said. Helpful bacteria, known as probiotics, are emerging as one of the good guys.

These bacteria, which reside in vast colonies in the gastrointestinal tract, exert a major influence on our well-being, according to researchers who study their attributes. Ensuring that these colonies thrive in a way that allows them to do their good work could lead to better health for many who now have a range of gastrointestinal disorders and allergies.

The colonies are in constant flux as major quantities of bacteria are eliminated daily, and others may be killed by antibiotics. One way to sustain those colonies is to ingest more of the beneficial bacteria in a product known as a probiotic. That's what Dr. Bonakdar's patient did.

Combating antibiotic-associated diarrhea is one of several research-supported uses for probiotics, which were defined in 2001 by the World Health Organization as "live organisms which, when administered in adequate amounts, confer a health benefit on the host."

Research in the area is growing rapidly, fueled by the search for a "natural" path to good health and further driven by the spread of antibiotic-resistant strains of harmful bacteria. The quest is on to find ways to help the white-hat bacteria do their jobs more efficiently to help fend off infections.

The organisms are often consumed in fermented milk products or via capsules, and they are also incredibly benign, Dr. Bonakdar said. Side-effects occur in fewer than 1% of people who take them, posing a risk only to some severely immunocompromised people.

Usually translated as "for life," probiotics long have been thought to confer a health benefit. Mention of cultured dairy products is found in the Bible, and soured milk was used therapeutically before microorganisms were even recognized, says the Physician's Desk Reference.

Food fermentation is one of the oldest methods for preserving foods. "Paleolithic humans used to eat much more bacteria," said Gregor Reid, PhD, a professor of microbiology and immunology at the University of Western Ontario Schulich School of Medicine and Dentistry. "We are the opposite. We try to kill everything that is in our food."

But that warlike stance could be changing as the bacteria's benefits are identified.

The case for probiotics

A growing number of scientific papers published in top journals are providing evidence for several health claims, said Sherwood Gorbach, MD, director of the nutrition and infection unit at Tufts University School of Medicine in Boston. Dr. Gorbach refined and patented a type of probiotic bacteria called Lactobacillus GG. It is marketed as a capsule called Culturelle and is among the most thoroughly studied of the probiotics.

It took Dr. Gorbach and his colleagues two years of screening thousands of lactobacilli to find the strain with the proper combination of attributes -- one that could survive the journey to the intestines and also had the potential to control other organisms in the gut.

It took 10 more years of research to determine whether there was any health benefit to be derived from it. Those benefits are continuing to emerge.

The evidence is strongest that the proper strain of probiotic can help prevent or shorten the duration of diarrhea, especially childhood diarrhea caused by the rotavirus, and antibiotic-associated diarrhea. Lactose-intolerant individuals also are found to have fewer symptoms if they consume a fermented dairy product instead of milk, Dr. Gorbach said in a recent paper.

Another area in which probiotics have been shown to be helpful is in the prevention and treatment of food allergies and childhood eczema.

W. Allan Walker, MD, professor of nutrition and pediatrics at Harvard Medical School in Boston, found the evidence of allergy prevention persuasive enough to urge his daughter to take probiotics when pregnant because she had allergies as a child. So far his grandchildren seem to have remained healthier than their young playmates, he said.

Anecdotes aside, the Lancet published in 2003 a well-constructed Finnish study showing that Lactobacillus GG given to pregnant women and to their infants who were thought to be at high risk for developing allergies cut the incidence of eczema in half as the babies grew, Dr. Walker said.

Studies are now exploring how bacteria that form colonies in the gut communicate with the intestinal epithelium to create a balanced, appropriate immune response, he added.

Michael Cabana, MD, MPH, director of general pediatrics at the University of California, San Francisco, is just beginning a study on probiotics and its effects on early markers of asthma. The study, sponsored by the National Heart, Lung and Blood Institute, is building on the 2003 finding. "The Finland study suggested that babies given probiotics developed less eczema, and eczema is associated with asthma," Dr. Cabana said.

The potential allergy benefit from exposure to microorganisms has a name, the "hygiene hypothesis." The theory says people who aren't exposed to a rich and varied group of microbes in their infancy are likely to be more predisposed to atopic disorders like allergies and asthma.

Some even credit the increase in allergies and asthma to the very sanitary conditions that cocoon young babies combined with the increased use of antibiotics and vaccines, Dr. Walker said. "All have been very effective at reducing infections, but they have also reduced the amount of intestinal exposure in the infant, and, as a result, an infant's immune system may not work as well as it should."

Probiotics also could prove helpful in preventing travelers' diarrhea, respiratory infections in children, dental caries, inflammatory bowel disease, intestinal inflammation in patients with cystic fibrosis, necrotizing enterocolitis in premature babies, irritable bowel syndrome and Clostridium difficile infection.

C. difficile can be particularly nasty, and outbreaks of a virulent strain recently swept nursing homes in the Great Britain, the United States and Canada, causing many deaths.

A cautionary note

Despite the promise of probiotics in regard to so many difficult conditions, researchers caution that only certain bacteria strains have been shown to convey health benefits, and it may be misleading to discuss probiotics in a generic sense.

Regardless, many products are advertised as probiotics even though the proof is lacking. It is such claims that damage the credibility of the entire field, researchers warn.

"Unfortunately everyone and their dog is calling everything a probiotic," Dr. Reid said. One company even has an aftershave lotion it promotes as a probiotic, he said. "That's why physicians think this whole area is a joke."

Not only must the strain of bacteria be correct, the quantity also must be sufficient. Each dose should have between 1 billion and 10 billion colony forming units, Dr. Gorbach said. "And if it doesn't say that on the label, then let the buyer beware."

Proper packaging is also crucial, Dr. Reid said; otherwise, all the bacteria could die.

Despite the extra effort it takes to find the real thing, many argue that the result is worth it.

Taking probiotics "should be an integral part of what we do in our lives," Dr. Reid said. "I would argue that there isn't a life phase that we go through where consumption of bacteria is not critical."

For example, during the first year of life an infant's immune system is programmed by the bacteria he or she is exposed to, Dr. Reid said. In adulthood there is clearly an association between bacteria, cardiovascular disease, cancer and many other chronic diseases, he said. "A study recently showed that probiotics can delay the onset of diabetes," he said. Probiotics also can help strengthen elderly people's waning immune systems.

Jeffrey Gordon, PhD, director of genome sciences at Washington University in St. Louis, advocates for peaceful coexistence with the vast invisible community of microbes in the gastrointestinal tract. "We have to have this extended view of ourselves as a life form that includes our gut."

He sings the praises of the multitudes of bacteria. "They are part of our genetic landscape and help define us both physiologically and genetically," he said. "They provide us with attributes that we have not had to evolve on our own. They break down nutrients that we can't degrade on our own. They also break down carcinogens."

Helping these organisms do their job means entering the realm of probiotics. The field is now poised to claim more medical acceptability, and researchers are working hard to provide the hard science to back the health claims established long ago.

To that end, an association of academic and industry scientists researching probiotics was formed in 2000. The purpose of the International Scientific Assn. for Probiotics and Prebiotics is to raise the field's credibility, said Dr. Reid, who is the group's secretary.

The scientific community has not, so far, been very accepting of probiotics, he said. "For someone to come along -- and believe me, we've done it -- and say, 'Listen, this simple food might actually work,' we get laughed at. We've heard laughter for 25 years now."

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Prebiotics -- by definition

Prebiotics are nondigestible food ingredients, often oligosaccharides, or short chains of sugar molecules, that are thought to stimulate the growth of beneficial bacteria, or probiotics, in the colon. Prebiotics, like probiotics, are sold commercially.

Source: AMNews reporting

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A yogurt a day won't necessarily keep the doctor away

Although it can be a healthy food, if only because of its calcium content, yogurt cannot generally be called a probiotic, noted Gregor Reid, PhD, professor of microbiology and immunology at the University of Western Ontario Schulich School of Medicine and Dentistry in London, Ontario.

For one thing, a cup of yogurt would not likely contain sufficient numbers of live cultures of good bacteria --somewhere between 1 billion and 10 billion colony forming units -- to convey a health benefit. In addition, the particular brand of yogurt might not contain a beneficial strain of bacteria, meaning one normally found in the human gut and known to provide a benefit.

Although most yogurts contain Lactobacillus acidophilus, that's not a bacterium naturally found in the gut. But some yogurts might contain Lactobacillus reuteri, which is a beneficial bacterium, said Jon Vanderhoof, MD, professor of medicine and pediatrics at the University of Nebraska Medical School in Omaha.

Another problem is that products like yogurt, while known to contain beneficial bacteria, often don't provide sufficient information on the label to allow a consumer to make an informed choice about the quantity of the live cultures or the strain of bacteria, said Mary Ellen Sanders, PhD, president of the International Scientific Assn. for Probiotics and Prebiotics.

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External links

The Physicians' Desk Reference on probiotics (link)

"Guidelines for the evaluation of probiotics in food," World Health Organization and the United Nation's Food and Agriculture Organization, 2002, in pdf (link)

International Scientific Assn. for Probiotics and Prebiotics (link)

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