Gut health is a hot topic these days, and I’ve been fielding lots of questions about the gut microbiota, as I’m sure many RDs working directly with consumers have. Along with probiotics, consumers are looking to prebiotics to make a health difference. In short, prebiotics are food for the good bacteria in the large intestine. The trillions of bacterial cells making the colon their home ferment various fibers to thrive. However, just as all nutritionists aren’t RDs, not all fermentable fibers are prebiotics.
According to the International Scientific Association for Probiotics and Prebiotics (ISAPP), a prebiotic is a compound selectively used by host microorganisms resulting in a health benefit to the host. Prebiotics alter the composition or the function of the microbiota. Key to this definition are selectivity and heath benefit. A prebiotic is fermented selectively, meaning that only beneficial microbes make a meal out of the compound. A fiber or other substrate that’s fermented by a large number of microbes with ill-defined health benefits doesn’t meet the ISAPP definition of a prebiotic.
Prebiotics can be likened to selective fertilizers, explains Randal K. Buddington, PhD, director of the prematurity and perinatal research program at The University of Tennessee Health Science Center. “Some fertilizers stimulate the growth of everything, including weeds. Prebiotics are like selective fertilizers. They stimulate the growth of just the desirable bacteria that have the ability to use prebiotics,” he explains. Furthermore, as healthy grass can discourage the growth of weeds, prebiotics may decrease pathogenic bacteria by helping the beneficial microbes to proliferate.
Identifying a Prebiotic
I’ve yet to find a consumer who can identify prebiotics on food labels; ingredient labels don’t identify prebiotics as such. Research currently supports the use of the term for only a few compounds, yet food manufacturers may erroneously claim prebiotic content on the front of the package. ISAPP confers prebiotic status to the following terms that clients may see on the ingredients labels of fortified foods or supplements:
- chicory root; and
Prebiotics also exist in small amounts in onions, garlic, bananas, and Jerusalem artichokes (sunchokes). Breast milk is a rich source of prebiotics.
Potential Health Benefits
ISAPP acknowledges that the health benefits of prebiotics are evolving. They currently include the stimulation of immune function, inhibition of pathogenic microbes, reduction in insulin resistance, and improvements in blood lipids, mineral bioavailability, and cognition.
RDs can use the following talking points when discussing prebiotics with clients and others.
A diverse diet is critical. While not all fermentable fibers are prebiotics, consuming a wide variety of fiber-containing foods promotes good health. I encourage my clients to meet or exceed the Recommended Dietary Allowance for fiber to promote heart health, manage blood glucose levels, lower cholesterol levels, reduce the risk of colon cancer, and normalize bowel habits. I remind them that, just as different vitamins have different functions, various fibers—even those that aren’t prebiotics—do too. They aren’t interchangeable, so we need to eat a varied, fiber-rich diet.
Dose matters. According to Buddington, the necessary dose of prebiotics depends on the desired health outcome. For example, 5 g daily might modulate the gut microbiota, whereas it might take 8 g daily to improve calcium absorption and upwards of 12 g daily to affect weight status.
Tolerance varies. Some people complain of gas and bloating when eating snack bars or other foods with chicory root or inulin. That’s because people vary in their tolerance to different fermentable compounds. For highly sensitive people, I recommend “start low, go slow.” Some snack bars have upwards of 8 g of inulin. While many people can eat a bar or two and not notice a thing in their intestines, others might feel miserable. To build tolerance, sensitive clients might eat just 1/4 of a snack bar daily for a couple weeks. They can then try 1/3 of the bar and increase their portion until they can handle more.
Provide your clients with further information via handouts from the ISAPP site.
— Jill Weisenberger, MS, RDN, CDE, FAND, CHWC, is a freelance writer and a nutrition and diabetes consultant to the food industry, including Dow AgroSciences and Egg Nutrition Center. She has a private practice in Newport News, Virginia, and is the author of several books, including Diabetes Weight Loss — Week by Week.