A large body of research over the past ninety years has demonstrated the preventive value of eating foods fermented with Lactobacilli or their cousins, Bifidobacteria. Eating these friendly bacteria prevents intestinal infection due to viruses or pathogenic bacteria and preserves intestinal permeability in the face of infection or other types of injury, can prevent antibiotic-induced diarrhea and travelers diarrhea and can lower serum cholesterol levels. Lactobacilli and Bifidobacteria also show anti-cancer activity, by two mechanisms: they inhibit the growth or activity of cancer-promoting bacteria and some strains actually produce chemicals which inhibit tumor growth.
Lactobacillus Species
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, unfortunately, 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 infections. 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 characteristics which lead it to grow especially well in the large intestine. The daily dose should be between one billion and ten billion viable bacteria. More may cause gastrointestinal irritation.
Lactobacilli not only colonize the intestinal tract but grow well in the vagina and the urethra, where they prevent growth of pathogenic bacteria. The application of vaginal spermicides like nonoxynol-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.