There are numerous species of Lactobacilli and many strains for each species. Some, like Lactobacillus acidophilus, are normal inhabitants of the human digestive tract. Others, like L. bulgaricus, which is a common starter for making yogurt, are not. L. bulgaricus disappears from the intestine within two weeks after yogurt consumption is stopped. Sauerkraut is sour because of L. plantarum, a beneficial organism that is normally found in the human intestine and that stays for a long time after being introduced. Commercially available fermented foods are, unfortu-nately, unreliable as sources of Lactobacilli, because the lactic acid and hydrogen peroxide which Lactobacilli naturally produce may kill the producers themselves if their concentration becomes excessive. A few years ago, the Annals of Internal Medicine published a study which proved what many women have known for years, that eating yogurt daily can prevent vaginal yeast infec-tions. The researchers were lucky. The batch of yogurt they gave their patients was loaded with living Lactobacillus acidophilus. These organisms not only took up residence in the intestines of the women who ate it, but also colonized the vagina, preventing yeast infection. When the scientists attempted to perform the same experiment a year later, they found that the same brand of yogurt contained no living bacteria.

The most reliable way to supplement your diet with Lactobacilli is to make your own yogurt or sauerkraut, or to buy nutritional supplements which have been tested by an independent outside laboratory and which list the concentration of viable bacteria found on culture. Lactobacilli are killed by heat, moisture and sunlight. The making of tablets generates heat which lowers the number of viable organisms. Lactobacilli should be freeze-dried, in powder or capsules, in opaque moisture-proof containers, stored in the refrigerator. They should be consumed with meals. The strains which have been most extensively tested for their viability in the human intestine are L.acidophilus strain NCFM-2 and L.plantarum. L. acidophilus is well-suited to growing in the small intestine, where it is normally one of the dominant bacterial species. L. plantarum has growth charac-teris-tics which lead it to grow especially well in the large intes-tine. The daily dose should be between one billion and ten billion viable bacte-ria. More may cause gastrointestinal irritation.

Lactobacilli not only colonize the intestinal tract, they grow well in the vagina and the urethra, where they prevent growth of pathogenic bacteria. The application of vaginal spermicides like nonoxyn--ol-9, found in many contraceptive creams, may kill Lactobacilli and give pathogens more ready access to the urinary tract. Taking Lactobacilli by mouth or inserting Lactobacillus capsules into the vagina, may restore genital tract symbiosis and prevent infection.

The beneficial bacteria which normally predominate in the large intestine are called Bifidobacteria. Declining levels of Bifidobacteria in the elderly allow accumulation of toxin-producing Clostridium species, which have been implicated in the development of cancer in the large bowel. Taking Bifidobacteria in a dose of three billion organisms per day, lowers the level of Clostridia in the bowel and also reduces the concentration of chemicals which are thought to promote cancer.

The growth of Bifidobacteria in the large bowel is strongly affected by diet. Bifidobacteria thrive on vegetable fibre and on the complex sugars that occur in certain vegetables. These complex sugars, known as fructooligo-saccharides (FOS), are especially concentrated in garlic, onion, artichoke, asparagus and chicory root. A synthetic form of FOS is available as a food supplement in the United States. Extensive research conducted in Japan, the U.S. and Europe demonstrates that supplementing the diet with FOS encourages the growth of Bifido-bacteria and discourages the growth of most undesirable bacterial species in the intestine. One teaspoon a day of FOS lowers the concentra-tion of toxic bacterial enzymes in the large intestine. These enzymes, called beta-glucuronidase and glycholate hydrolase, are able to convert normal constituents of the stool, derived either from food or from bile, into carcinogens (chemicals which cause cancer). Regular consumption of foods rich in FOS may de-crease the risk of colon cancer.

"Nutritional yeast" has been used as a dietary supplement for generations, as a source of vitamins and minerals and for treatment of digestive complaints. After treating hundreds of yeast-allergic patients, I was very reluctant to prescribe yeast for anyone, until I discovered a preparation which the French call "Yeast Against Yeast". The yeasts which invade human tissues, causing yeast infection, are mostly members of the genus Candida. The yeast used in baking bread or brewing beer belong to the genus Saccharomyces. Yeast Against Yeast is Saccharomyces boulardii, a microbe which inhabits the surface of many different plants and which was first isolated from lichee nuts in Southeast Asia by French scientists during the 1920's. Saccharomyces boulardii has been used in Europe for decades to treat acute diarrhea and controlled trials have shown it effective in preventing or treating diarrhea brought on by antibiotics. S. boulardii appears to exert its beneficial affects by inactivating bacterial toxins and by stimulating intestinal immune responses . S. boulardii has been available in natural food stores in the United States since 1991. People who are allergic to baker's yeast may also be allergic to S. boulardii, but for most people, including women with chronic Candida infection, Yeast Against Yeast lives up to its name.