Linda F. Benedict, Tulley, Richard T., Martin, Roy J, Keenan, Michael J., Aryana, Kayanush J., Janes, Marlene E., Greenway, Frank
Michael J. Keenan, Kayanush J. Aryana, Marlene E. Janes, Aixin Hou, Roy J. Martin, Richard T. Tulley, Frank L. Greenway, Nikhil V. Dhurandhar and Jun Zhou
After birth, every person’s gastrointestinal tract (gut) becomes filled with microorganisms, mainly bacteria. These are often referred to as our microflora. The majority of these are located in the large intestine. In fact, there are more bacterial cells in a person’s gut than cells in the entire body. Bacteria feed on food components that escape digestion in the stomach and small intestine and nutrients that escape absorption. These components are mainly fibers.
One method for categorizing fibers is into fermentable and nonfermentable. Bacteria can break down the fermentable fibers into various products. One of the most common groups of products is short-chain fatty acids. The major three short-chain fatty acids are butyric acid (four carbons), propionic acid (three carbons) and acetic acid (two carbons). The production of short-chain fatty acids is believed to improve the health of the gut by improving nutrient absorption, preventing diseases such as colon cancer and improving the condition of patients with inflammatory bowel disease. Butyric acid is considered especially beneficial to the health of the gut.
LSU AgCenter research focuses on the interaction between bacteria and fermentable fiber food and its effect on body fat and obesity. Researchers believe beneficial bacteria in the gut can produce greater health throughout the entire body.
Probiotics are beneficial bacteria in the gut. Prebiotics are the food for the bacteria. Both probiotics and prebiot ics are fairly common in yogurt-related products. They are also sold as supplements in health food and grocery stores. Yogurt is a good vehicle for delivering beneficial bacteria to the large intestine. Once in the large intestine, the bacteria grow and impart beneficial health effects to the human host.
Prebiotics are fermentable fibers such as resistant starches – long chains of glucose molecules "resistant" to digestion in the stomach and small intestine – and chains of other types of linked sugar molecules – such as fructose in fructooligosaccharides – for which the small intestine has no enzymes to digest the link.
Resistant starch is high in one type of starch called amylose. The commonly sold starches in grocery stores are low in resistant starch because the main starch component is the other major type known as amylopectin. Amylopectin also consists of long chains of glucose molecules. But unlike amylose, amylopectin has multiple branches that make it more accessible to digestion by amylase enzymes in the small intestine.
The availability of resistant starch is increasing and is available for use in baking such products as breads, cookies or muffins. From 10 percent to 50 percent of the flour in these products can be replaced with the resistant starch product.
The prebiotic found in yogurt and also sold in supplement form is fructooligosaccharide. A variety of different types of fructooligosaccharides are composed of chains of fructose in a variety of lengths or number of fructose molecules. Both resistant starches and fructooligosaccharides are fermented by several groups of bacteria that appear to benefit our health when they increase in number in our gut.
Researchers have reported that lean people have a different overall profile of gut microflora than overweight and obese people. When the gut microflora from obese rodents have been transferred to the gut of lean rodents, the lean rodents increase their body fat. Obese people appear to have a greater amount of the bacteria that break down the fermentable fibers and thus recover more energy from the fermentable fibers in their large intestine. The resistant starch research team at the LSU AgCenter and Pennington Biomedical Research Center, however, has demonstrated that increases in several types of bacteria that break down resistant starch result in rodents with less body fat. Research by others also demonstrates reduced body fat with the addition of fructooligosaccharides to rodent diets.
Further research is necessary to determine the differences in gut microflora among obese individuals and individuals consuming diets high in resistant starches or fructooligosaccharides. AgCenter researchers are continuing to study rodents to determine why animals fed fermentable fibers have less body fat. The hypothesis is that the short-chain fatty acids, especially butyric acid, cause endocrine cells in the gut to produce hormones that travel to the brain. The brain then signals the muscle, liver and fat tissues to burn more fat for energy.
AgCenter researchers already have demonstrated short-chain fatty acids can be increased in the guts of rodents fed resistant starch. This, in turn, resulted in increases in blood levels of two gut hormones – peptide YY and glucagon-like peptide 1 – and an increased amount of proopiomelanocortin – an important brain signal involved in energy balance. Finally, increased body fat utilization (or burning) leads to decreased obesity.
Human feeding trials are also under way. One involves feeding children yogurt containing resistant starch to determine if the resistant starch produces the same effects on gut microflora as observed in laboratory animals. Another human study shows diets containing a resistant starch increased blood levels of the same gut peptides observed in AgCenter animal studies – peptide YY and glucagon-like peptide 1. Subjects fed resistant starch on reduced-calorie diets reported feeling less hungry and had greater feelings of fullness during the study.
In the future
The LSU AgCenter Biotechnology Interdisciplinary Team program has awarded a grant to conduct a comprehensive molecular characterization of gut microflora from animals fed a fermentable fiber that has been shown to reduce obesity and blood lipids and improve glucose clearance. Researchers will use the data collected on gut microbial diversity to do the following:
Michael J. Keenan, Associate Professor, School of Human Ecology; Kayanush J. Aryana, Associate Professor, School of Animal Sciences, LSU AgCenter; Marlene E. Janes, Associate Professor, Department of Food Science, LSU AgCenter; Aixin Hou, Assistant Professor, Environmental Studies, LSU; Roy J. Martin, Professor and Director, and Richard T. Tulley, Professor, School of Human Ecology, LSU AgCenter; Frank L. Greenway, Professor, Nikhil V. Dhurandhar, Associate Professor, and Jun Zhou, Instructor, Pennington Biomedical Research Center, Baton Rouge, La.
(This article was published in the fall 2008 issue of Louisiana Agriculture.)