In school, my daughter is studying the diversity of ecosystems from the Great Barrier coral reef near Australia to the equatorial rainforests of the Amazon River basin. Her eyes widened when I described to her the amazingly complex ecosystem hidden in the dark recesses of our intestines.

As many as 500 different species of bacteria form a society there, in a delicate balance with each other and with their ‘earth’ – us. We are outnumbered in our own bodies – there are more bacterial cells in us and on us than there are human cells. The beneficial bacteria produce critical enzymes that we need for our health. When everything is going well, we all benefit.

But sometimes things don’t go so well. When we take an antibiotic, it can be like clear-cutting rainforest land. Entire species are eliminated. It’s a devastating emergency for the species there.

The short-term results of taking antibiotics include diarrhea (comparable to erosion) and yeast infections (as more primitive species takes over the vacated niches). The opposite of antibiotics are probiotics – a term coined in 1965 to describe substances that favor the growth of beneficial microorganisms in the body.  The idea of giving yogurts and fermented milks to promote health has been around for millennia  – far older than most old wives’ tales. Buttermilk, feta cheese, and active-culture yogurts are among the foods that have been used. Almost a century ago, Russian microbiologist Elie Metchnikoff suggested that consuming the live microbes in fermented milk products may be, at least in part, responsible for the longevity of certain ethnic groups. Is this quackery or solidly scientific? A flood of recent research made probiotics a hot topic at the World Congress on Pediatric Gastroenterology, Hepatology, and Nutrition in August 2000. Two species of probiotics, Bifidobacterium and Lactobacillus, have been the most studied.  Some benefits have been well established for some time. Bacteria that produce the enzyme lactase will help reduce lactose intolerance.  Probiotics can treat other enzyme deficiencies (e.g. sucrase maltase deficiency) as well. Could probiotics be used to counteract episodes of diarrhea that are caused by antibiotics? In a placebo-controlled study, Lactobacillus was given to children along with antibiotics, resulting in fewer cases of diarrhea and milder diarrhea for those who did get it. How about treating other types of diarrhea? Active-culture foods are somewhat effective at preventing and treating bacterial diarrhea, including Clostridium, Shigella, Salmonella, and the dreaded E. Coli 0157:H7.

A Gut Reaction

It makes sense that active cultures should help diarrhea caused by either destruction of beneficial bacteria or by invasion of disease-causing bacteria. But viral diarrhea takes place on a different playing field. Surprisingly, Lactobacillus is most effective at preventing and treating rotavirus and other viral infections. This suggests that probiotics are not just friendly placeholders in the gut, but active immune enhancers. Indeed, randomized, double blind, placebo-controlled trials have found significant, measurable increases in markers of immune function in those with active cultures in the diet.  Perhaps it would be better to say that probiotics modulate the immune response – keeping it in the normal level — by also protecting against inflammation and autoimmunity. By reducing inflammation, probiotics appear to be useful in treating a variety of gastrointestinal problems including inflammatory bowel disease (such as Crohn’s disease or ulcerative colitis), ulcers, and irritable bowel syndrome. Flatulence and non-specific tummy aches can also be decreased.

But the effect goes far beyond this….

Food allergies are caused by the production of antibodies (IgE) against something in the diet. Normally, a substance in our bodies called interleukin 12 (IL-12) prevents this. A recent study showed that consuming Lactobacillus can increase IL-12, decrease IgE antibodies, and thus help prevent and treat food allergies. Many children with eczema have flare-ups triggered by what they eat or drink. In one fascinating study, a group of children who received Lactobacillus had significant improvement of their eczema within one month!

Lactobacillus in yogurt also has a weakly protective effect against asthma by stimulating interleukin and TH 1 cells. (It has some gentle anti-tumor properties by the same mechanism.) Some evidence suggests that the recent increase in childhood asthma may be partially from the destruction of our normal, healthy bacteria. And in at least one study of 571 children, there was a significant reduction in respiratory infections (including sinusitis, bronchitis, and pneumonia) in the children taking Lactobacillus.  One of the most startling recent studies of Lactobacillus indicated a “marked, long-term” protective effect on the heart, preventing and decreasing damage from lack of oxygen to the heart muscle. The effect was attributed to the demonstrated changes in inflammation and the immune system.  A recent double-blind, placebo controlled trial found that some strains of active-culture yogurt, eaten over 8 weeks, help lower LDL cholesterol and normalize blood pressure. Serum triglycerides were also lowered in a controlled animal study.

A healthy internal environment of beneficial bacteria can also protect the body from toxins. Aflatoxin, a highly toxic substance found in foods including peanut butter and alfalfa sprouts, can be intercepted by Lactobacillus.  Probiotics can protect against food poisoning. Similarly, a diet high in Lactobacillus can block much of the liver damage that would be caused by excess alcohol. Because probiotics can decrease the presence of carcinogens in the intestines in several ways, they may prove helpful for preventing cancer. This would protect against colon cancer, as one might expect, but the effect may extend to other cancers as well. One important study suggests that in the soy-rich Japanese diet that seems to prevent breast cancer, it is the abundance of the probiotic Bifidobacterium in some soy products that is at least partly responsible for the powerful preventive effect. This will be an important area of study in the future.

Along the same lines, it may be the Lactobacillus in wine that is responsible for some of the health benefits

Material taken from papers written and accepted by the National Research Council’s “Nutrient Requirements of Horses”