Physiological effects of consumption of fructo-oligosaccharides and transgalacto-oligosaccharides.

Oligosaccharides naturally occur in many raw materials that are used for the manufacture of human foods. Plant oligosacccharides are often not digestible in the upper part of the gastrointestinal tract, but may be fermented in the colon by the intestinal microflora. These non-digestible oligosaccharides are often considered dietary fiber.We studied the effects of two types of oligosaccharides, fructo-oligosaccharides and transgalacto-oligosaccharides, in humans using placebo controlled interventions. Special emphasis was put on measuring fermentation and on the effects on the composition of the intestinal microflora, putative colon cancer risk markers and glucose and lipid metabolism.We showed that healthy volunteers ferment fructo-oligosaccharides and transgalacto-oligosaccharides completely, as measured by the recovery of the oligomers in feces. The apparent fermentability of fructo-oligosaccharides by patients with an ileal pouch-anal anastomosis was 83%. Fermentation of both fructo-oligosaccharides and transgalacto-oligosaccharides increased the excretion breath hydrogen. When hydrogen is produced, most bacteria simultaneously produce short-chain fatty acids, but the fecal concentration of short-chain fatty acids after consumption of either fructo-oligosaccharides or transgalacto-oligosaccharides was not increased. Rapid absorption of the acids by the colonic mucosa probably occurred.We showed substrate specific changes of bacterial glycosidase activity in fecal water after dietary intervention with non-digestible oligosaccharides and conclude that the glycolytic activity of the intestinal bacteria might be a useful biomarker of the colonic metabolic activity.We found no effects of transgalacto-oligosaccharides on the composition of the intestinal microflora of healthy volunteers, when tested in a controlled feeding trial against a placebo treatment. There were no effects of fructo-oligosaccharides and transgalacto-oligosaccharides on stool weight or on the fecal concentration of butyrate, nor effects of transgalacto-oligosaccharides on fecal bile acid profiles or on the concentration of fecal toxic protein fermentation products.We showed that fructo-oligosaccharides do not favorably affect fasting glycaemia or serum lipids in non-insulin dependent diabetic patients that are under strict medical control for their diabetes. Although fructo-oligosaccharides and transgalacto-oligosaccharides are completely fermented, we were unable to find any evidence that they beneficially affect putative colon cancer risk markers, the composition of the intestinal microflora or glucose and lipid metabolism. It remains possible that they have effects in other study-populations, when tested against another background diet or when combined with other fermentable substrates