Today’s Dietitian talks with
Hannah Holscher, PhD, RD, about Prebiotics and the Gut Microbiome
Hannah Holscher, PhD, RD
Due to the overwhelming success of Hannah Holscher’s Lunch presentation during the 2022
Today's Dietitian Spring Symposium the BENEO-Institute is making available this follow-up Q&A with Hannah Holscher, PhD, RD.
Dr. Hannah Holscher is an Associate Professor of Nutrition in the Department of Food Science and Human Nutrition and a member of the Division of Nutritional Sciences, the Institute of Genomic Biology, and the National Center for Supercomputing Applications at the University of Illinois. She completed postdoctoral training focused on the human microbiome, a Ph.D. in Nutritional Sciences, and a B.S. in Food Science and Human Nutrition at the University of Illinois. She is also a Registered Dietitian.
Today’s Dietitian (TD): What triggered your interest in studying the gut microbiome?
Holscher: I’ve always loved science and solving complex problems. So, when I learned about this vast ecosystem of microorganisms within our bodies that plays a role in interacting with our diet and contributing to health, I was very intrigued.
TD: The knowledge of the role of the gut microbiome and its exchange with the host is developing very fast. Will you please explain where we are in this journey and describe the main functions of the gut microbiome?
Holscher: The gut microbiota has a range of functions. You can broadly categorize the functions into three categories: metabolic, immunologic, and protective. For metabolic functions, this relates to interacting with dietary components. So, the microbiota can break down nondigested substrates like dietary fibers and proteins. They can also synthesize secondary bile acids from the primary bile acids that our bodies make to emulsify, digest, and absorb fat. The gut microbiota can also synthesize vitamins, including a range of B vitamins as well as vitamin K. Specific to immunologic functions, the microbiota plays a role in stimulating the production of immunoglobulin A and influencing T cells. For the protective functions, one of the things that relates to our diet is the gut microbiota’s ability to ferment dietary fibers and prebiotics and generate short-chain fatty acids. Short-chain fatty acids reduce the pH within the intestinal lumen, which reduces the ability of certain pathogens to be able to survive in the gut. The production of short-chain fatty acids also helps strengthen our intestinal barrier function.
TD: After hearing about the positive influence of the gut microbiome on health, how can we influence our gut microbiota ecosystem to benefit our health?
Holscher: It’s important to aim to consume the recommended amount of dietary fiber each day, which is around 25 g per day for women and 38 g per day for men. A good general recommendation is to “eat the rainbow.” That’s because consuming lots of different types of vegetables, fruits, whole grains, legumes, and nuts also helps provide lots of different types of dietary fiber that gut microbes can use as an energy source. Another important source of nutrients for the gut microbiota is prebiotics. Prebiotics are substrates that are selectively utilized by host microorganisms conferring a health benefit. You can find prebiotics in plant sources like leeks and garlic, onions, artichokes, wheat, and bananas. You can also find prebiotics in lots of different food sources like breakfast cereals and cereal bars. When looking for prebiotics within food sources, you’ll want to look at the ingredients list and look for terms like inulin or fructo-oligosaccharides, or galacto-oligosaccharides.
TD: You mentioned prebiotics. Why do we need to pay attention to the use of the word prebiotic? Aren’t all fibers prebiotic anyway?
Holscher: No. Not all fibers are prebiotics. There are lots of different types of fibers. The term fiber is regulated by the FDA and is defined as “nondigestible soluble and insoluble carbohydrates that are greater than or equal to 3 monomeric units and lignan that are intrinsic and intact in plants; isolated or synthetic nondigestible carbohydrates that are greater than or equal to 3 monomeric units determined by the FDA to have physiological effects that are beneficial to human health.” The term prebiotic was defined by scientists. Specifically, a panel of experts was organized by the board of directors of the International Scientific Association for Probiotics and Prebiotics, also known as ISAPP. They defined prebiotics as a substrate that is selectively utilized by host micro-organisms conferring a health benefit. Currently, the substrates that are accepted as prebiotics fall within a couple of categories of dietary fibers. Specifically, inulin-type fibers and galacto-oligosaccharides are accepted as prebiotics.
TD: What are the main benefits of prebiotic inulin-type fructans that are mediated by the gut microbiome?
Holscher: We recently published a systematic review in Advances in Nutrition that summarized the health benefits of consuming inulin-type fructans.1 In that review, we noted that when adults consumed inulin-type fructans, they have benefits including increased intestinal absorption of minerals like calcium and magnesium, improved satiety, improved intestinal barrier function, improved laxation, improvements in their blood lipid profile and triglycerides, and improvements in insulin sensitivity. Importantly, health benefits of inulin-type fructans have also been reviewed by regulatory authorities. For example, the European Food Safety Authority, or EFSA, supports the claim that “chicory inulin contributes to the maintenance of normal defecation by increasing stool frequency.” Within the United States, the FDA has determined that evidence supports beneficial physiological effects on bone mineral density and calcium absorption when individuals consume inulin.
TD: What are your recommendations to increase intake of prebiotic inulin-type fructans, and what intake should we aim for?
Holscher: You need to consume at least 3 g per day. However, upwards of 5 g per day may be necessary, depending on your total caloric intake. You can find inulin-type fructans in varying amounts within plant sources like leeks, garlic, and onions. Artichokes are also high in inulin-type fructans. As I’ve also mentioned, inulin-type fructans can be found in many different food sources—everything from soups and sauces to beverages, bars, and desserts. In these cases, you’re going to need to look closely at the ingredients list to determine if it contains inulin-type fructans. There are lots of names that these can be listed as they include inulin, inulin from chicory, chicory fiber, chicory root extract, chicory root fiber, chicory root, chicory vegetable fiber, oligofructose-enriched inulin, oligofructose, and fructo-oligosaccharides. So, take a close look at the ingredients label so that you can determine if the food product contains prebiotic fibers.
Please check www.dietaryfiber.org for more information on prebiotic inulin-type fructans.
Reference
- Hughes RL, Alvarado DA, Swanson KS, Holscher HD. The prebiotic potential of inulin-type fructans: a systematic review. Adv Nutr. 2022;13(2):492-529.
