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Health Benefits of Probiotics The health benefits of probiotics include maintenance and restoration of the GI barrier function, support of the immune system, reduction of constipation and diarrhea, improvement of digestion and availability of nutrients, and reduction of microbial pathogens and toxic substances.3

Prebiotics

Prebiotics are nondigestible, fermentable carbohydrates that stimulate and promote activity of beneficial gut bacteria. Prebiotics are the booster substance for probiotics. A natural example of this is found in human milk. Human milk contains small oligosaccharides that are undigestible by newborns. The role of these oligosaccharides in human milk was not at first understood and, in fact, researchers questioned why human milk would contain components unusable by the newborn infant. Researchers provided the explanation when they found that these small oligosaccharides were fueling beneficial bifidobacteria found in the newborn’s gut. The prebiotic oligosaccharides in human milk are specific to human milk. However, this model has provided interest among food scientists in adding oligosaccharides to foods and beverages—one example is infant formula—to enhance the growth of beneficial bifidobacteria.

Prebiotic Approach

The prebiotic approach uses whole foods with these nondigestible carbohydrates to stimulate growth and promote activity in beneficial bacteria, especially bifidobacteria. As the beneficial gut microbes increase in number, pathogenic bacteria such as Salmonella, Campylobacter, and E. coli decrease. Ingesting prebiotics is a practical way of manipulating the microbiota, since they support and increase the beneficial bacteria population in the gut. Together, probiotics and prebiotics are an important duo. In addition, prebiotic fibers are components of the healthiest foods on the planet—natural plant foods.

Food Sources

Food analysis research continues to appear in the literature, focusing on food composition, especially on fermentable fibers. However, many scientists consider the true test for a prebiotic food or ingredient to be, “Does it have a prebiotic effect when fed to humans?” Studies in rats precede human studies, and there have been a few human trials. Trials continue to emerge, often funded by food commodity groups. Recent human studies of individual foods include wild blueberries, kiwifruit, almonds, and green tea, all of which exhibited prebiotic activity. Analyses of foods continue; for example, the California Raisin Marketing Board analyzed raisins. On the horizon are analyses of oat, corn, and other grains. This listing of whole-plant food sources that contain prebiotic fiber is a valuable resource.

Benefits of Fermentation

When the nondigestible carbohydrates in the prebiotic plant foods reach the lower bowel, the gut microbes go into action. This process, which results in the production of acids and gases, is fermentation. The benefits of fermentation include acids decreasing the pH level of the colon, which is detrimental to the survival of pathogenic bacteria; short-chain fatty acid production, which proWWW.SFMS.ORG

vides fuel for the beneficial bacteria; enhanced mineral absorption, especially calcium and magnesium; and enhanced immunity.3

Eating for Gut Health

How should physicians advise their patients on how often to eat probiotic and prebiotic foods? Patients can be directed to eat probiotic foods every few days to replenish the gut microbiota. Presently it is thought that probiotics do not take up permanent residence; rather, they do their job while in the gut and then pass out in the stool. Physicians may counsel patients to eat prebiotic foods every day to feed and support healthy gut microbes. When introducing new whole plant foods to their diet, patients should eat them in small servings and increase as tolerated. Two diets that emphasize prebiotic foods, which physicians can recommend to patients, are the DASH diet and the Mediterranean diet, as both encourage numerous servings of vegetables and fruits. Physicians might suggest to patients that they use yogurt or kefir as the dairy choices in these diets to provide probiotic foods.

Key Message

“The health of the gut is enhanced with a diet rich in pre- and probiotics.” Physicians can use this message with patients and follow up by asking, “What new pre- and probiotic foods are you eating?” Over time, patients will exhibit changes in their eating patterns, accompanied by improved gut health. Jo Ann Hattner and Susan Anderes have been working together since 1999 on Stanford Medical School’s online nutrition courses— Jo Ann as a content writer and Susan as the webmaster and medical librarian. They collaborated on writing Gut Insight (published in 2009) and updating Help! My Underwear Is Shrinking (second edition released in 2013), and they continue to work together on numerous professional presentations and papers. A full list of references is available online at www.sfms.org.

Prebiotic Foods Fruits

apple, banana,* berries, raisins, wild blueberries, kiwifruit, agave

Vegetables

Onion,* garlic,* leeks,* shallot,* Jerusalem artichoke,* globe artichoke,* asparagus,* chicory root,* burdock,* yacon,* jicama, tomato, mushrooms, greens: dandelion,* salsify,* spinach, collard, chard, kale, mustard

Legumes or pulses lentils, dry beans, chickpeas, peas Whole grains

Seeds and nuts Other foods

whole wheat,* barley,* rye,* oats, brown rice, corn, buckwheat flaxseed, almonds honey, green tea

*Foods documented in the scientific literature as containing nondigestible, fermentable carbohydrates. The other foods listed have been analyzed for content or studied in vitro or in vivo in humans or animals.7-9 Prebiotic food references can be found at www.gutinsight.com.

SEPTEMBER 2014 SAN FRANCISCO MEDICINE

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September 2014