Prebiotics and Synbiotics

Prebiotics are nondigestible simple sugars (oligosaccharides) sold as pills and liquids that stimulate the growth and/or activity of “friendly” bacteria already present in our intestines. Prebiotics are very effective for relieving constipation, and hold some promise for the prevention of gallstones and for the treatment of inflammatory bowel diseases.   Examples of undigestible sugars used as prebiotics are: FOS (fructooligosaccharides), GOS (galactooligosaccharides), inulin (not insulin), lactulose, and lactitol.  Two prebiotics prescribed by doctors, lactulose and lactitol, have been effectively used to treat patients with liver failure (hepatic encephalopathy).⁵  They may also be helpful in the prevention of colon cancer.^13,14

These commercial products have no toxic effects.  They can act as a mild laxative in small amounts, but may produce flatulence when consumed in large amounts. Combining probiotics (the bacteria) with prebiotics (the bacteria’s food) results in a logical partnership, called synbiotics. You will most often find synbiotic products sold as mixtures of bacteria with FOS. Because the McDougall diet is made of starches, vegetables and fruits which contain a wide variety of undigestible sugars that feed and stimulate the growth of “friendly” bacteria, people consuming such a diet require not additional prebiotics to obtain optimal health benefits form their microflora (natural or enhanced by probiotics).

Prebiotic foods (e.g., oats, asparagus, beans, sweet potatoes, leeks, onions, and garlic) foster growth of friendly gut bacteria. Probiotic plant foods (e.g. sauerkraut, kimchi, kombucha, nondairy yogurts, and tempeh) deliver live, beneficial bacteria to the gut. Probiotics can also be found in pill form, but the most effective way to increase healthy gut bacteria is simply to eat the right foods — namely, plants!

What makes beans special?

Beans, lentils, split peas, and other legumes are rich in fiber and resistant starch, carbohydrates that cannot be broken down by human digestive enzymes.

The bacteria that reside in the large intestine depend on “microbiota-accessible carbohydrates,” also known as prebiotics, to survive; prebiotics are food for gut bacteria. Without enough prebiotics in our diet, gut bacteria begin to consume an alternative energy source: the first line of our immune defense on the surface of the intestinal lining. This intestinal lining is made up of molecules called mucins.³

All plant foods contain some prebiotics, but beans are special because they are very high in resistant starch, making them especially rich in prebiotics. Not all indigestible plant carbohydrates act as prebiotics, but resistant starch from beans provides large amounts of prebiotics. Prebiotics nourish the microbiome and allow for production of SCFAs.³

So the fiber and resistant starches from beans are waiting in our digestive tract and full of microbiota-accessible carbohydrates. To sum it up, we eat beans because they nourish our microbiome and  promote production of short chain fatty acids. SCFAs help kick our immune system into gear.