Bowel Function

Inulins and fructooligosaccharides in the diet promote gastrointestinal health and improve bowel function. They do this primarily by contributing to dietary fiber — a heterogeneous group of plant-derived carbohydrates that are not digested by human enzymes and are not absorbed in the small intestine (Flamm et al., 2001). Dietary fiber plays an important role in nutrient absorption, digestive transit time, and stool composition and quantity, while providing the main nutrient source for colonic microflora (Trepel, 2004). Through its effect on the colonic microflora, dietary fiber has a bulking effect. In general, for every additional 1 g of dietary fiber consumed, stool weight increases by up to 5 g (Roberfroid et al., 2002a).

Fermentation products arising from the metabolism of prebiotics by colonic microflora, such as bifidobacteria and lactobacilli, include vitamins and short-chain fatty acids. These are largely absorbed in the colon and are metabolized to provide energy for the body. Probiotics containing strains of bifidobacteria have been shown to raise levels of water-soluble vitamins (e.g., thiamine, nicotinic acid, folic acid, and vitamin B12) in the large intestine (Deguchi et al., 1985; Lee et al., 1999). Short-chain fatty acids comprise acetates (e.g., acetic acid), propionates (e.g., propionic acid), butyrates (e.g., butyric acid), and lactates (e.g., lactic acid). They exert systematic effects on the metabolism of carbohydrates, fats, and cholesterol, and are vital for normal colonic function (Hidaka et al., 2001). The types of fermentation products arising from digestion depend on the makeup of the intestinal microflora and the amount and structure of the inulin and fructooligosac-charides present. The fermentation and digestion of prebiotics increase the amount of bacterial biomass and raise intestinal levels of carbon dioxide, hydrogen, and methane, in addition to short-chain fatty acids (Andrieux et al., 1993; Roberfroid et al., 2002a).

Fructooligosaccharide supplements (e.g., 3 gday-1) improve bowel function by relieving moderate constipation and increasing stool frequency (Kameoka et al., 1986; Tokunaga et al., 1993; Tominaga et al., 1999; Wolf et al., 2003). Inulin and fructooligosaccharides lower intestinal pH and increase the weight of the stools, while also raising the levels of butyrate and other gaseous fermentation products (Campbell et al., 1997). Stool weight in humans can be increased by about 20% and breath hydrogen by around three-fold (Alles et al., 1997). The production of short-chain fatty acids reduces pH, while the increase in stool weight is mainly attributable to increased microbial biomass in the colon. As the water content is high, stools are softer and easier to expulse — thereby increasing stool frequency (Churbet, 2002).

Gastrointestinal disturbances can lead to several types of diarrhea, such as pseudomembranous colitis (caused by overgrowth of Clostridium difficile), rotavirus diarrhea, antibiotic-associated diarrhea, and travelers' diarrhea. Prebiotics and synbiotic supplements containing bifidobacteria with inulin or fructooligosaccharides have the potential to treat these conditions (Gibson et al., 1997). Travelers are prone to gastrointestinal disorders, through exposure to unfamiliar strains of microorganisms in food and drink. A trend toward fewer attacks of diarrhea and a better sense of well-being were reported for a group of travelers taking fructooligosaccharide supplements (10 gday-1) compared to a control group (Cummings et al., 2001). Patients just recovered from the diarrhea symptoms of C. difficile infection receiving fructooligosaccharides (12 g day-1) had higher levels of bifidobacteria than controls after 12 days and were less likely to suffer relapses of diarrhea (Lewis et al., 2005).

Low Carb Diets Explained

Low Carb Diets Explained

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