By Joyce Hendley, M.S., "Can Fermented Foods Really Help Your Health?,"November/December 2010
Reams of research have looked into the health effects of probiotic (“good”) bacteria that ferment our foods. But most of these trials test specific strains of bacteria delivered in supplement form—or via a heavily fortified food, such as a yogurt that bills itself as probiotic-enhanced. (All yogurts contain probiotics; some manufacturers add large amounts of specific strains of probiotics associated with certain health benefits.) These probiotic strains are often patented by the manufacturers who paid for the research. Sometimes the products tested are prototypes that aren’t yet available to consumers. For example, a preliminary study published in a 2010 issue of European Journal of Clinical Nutrition suggests that a fermented milk drink fortified with a strain of bacteria called Lactobacillus gasseri, or LG2055, might help people to lose belly fat.
But we can’t buy this drink—nor can we assume that other strains of probiotics might offer similar benefits to LG2055.
So what does research actually say about the probiotics in foods like yogurt, sauerkraut, kimchi? We sift through the science.
Some research suggests that when “good” bacteria reach the lower intestine, they not only suppress the growth of “bad” bacteria but also might activate the immune system to fight off diseases in other ways. But studies showing a clear boost to the immune system are few. In one study of 33 healthy young women, both “regular” yogurt and so-called “probiotic-fortified” yogurt (which contained added beneficial bacteria cultures) were found to boost T-cells, key players in the body’s defenses against viruses and other pathogens. But it’s a long way from findings like those to “assuming that by loading up on yogurt—or sauerkraut or kimchi—you can boost your immune system enough to fight off something like the H1N1 flu,” says Barry Goldin, Ph.D., professor in the department of Public Health and Community Medicine at Tufts University School of Medicine in Boston. Fortifying yourself with a daily dose of fermented foods can’t hurt, says Goldin, “but if you want to beat the flu, get vaccinated.”
When milk is fermented to make yogurt or kefir, it’s easier to digest in general: the bacteria that do the fermenting remove most of the lactose (milk sugar) so that alone makes these products easier for people with lactose intolerance to handle without stomach upset. Yogurt might also prevent gastrointestinal distress by helping to restore populations of healthy bacteria knocked out of balance by antibiotic treatment. In one study of 202 hospitalized patients receiving antibiotics, those who were given a twice-daily cup of yogurt were half as likely to develop diarrhea than those who had no yogurt.
But beyond GI upset associated with antibiotics, there’s little research that shows standard yogurts improve other digestive problems like constipation or Irritable Bowel Syndrome. There is some evidence, however, mostly from their manufacturers, that probiotic-enhanced yogurts, such as Activia and Yo-Plus, can help reduce such symptoms. “Regular” yogurt might help with these conditions, too, “but it just hasn’t been studied the way some probiotic[-enhanced] yogurts have,” says Mary Ellen Sanders, Ph.D., an internationally recognized probiotic microbiologist and consultant. If you have a specific digestive problem, you might consider looking for a probiotic-enhanced product that advertises that it contains strains of bacteria shown to be helpful for your condition.
Some fermented-foods advocates believe that probiotics might increase the body’s resistance to the ultimate invaders: cancer cells. Recently, Swedish researchers at Stockholm’s Karolinska Institute looked at dietary and cancer data from more than 82,000 Swedish men and women over a nine-year period. They found that those who averaged two or more daily servings of yogurt or fermented-milk products had a 38 percent lower risk of developing bladder cancer when compared with those who never ate those foods. Other studies hint that people who regularly eat yogurt might have a reduced risk of developing colorectal cancer.
When it comes to fermented vegetables, however, data from Asian studies add a note of caution. A Chinese study found that the more fermented foods men ate daily—particularly pickled vegetables—the higher their risks of developing prostate cancer; Korean research has found links between heavy kimchi consumption and increased risk of stomach cancers. Although epidemiologic studies like these aren’t designed to show a clear cause or effect, researchers note that the nitrates naturally occurring in the vegetables—and the high amounts of salt added to pickle them—are both known to increase stomach cancer risk.