The objective of the present study was to determine whether acacia gum (GUM) is a prebiotic fibre and to evaluate its intestinal tolerance in healthy subjects. The effects of increasing doses of GUM were compared to those of sucrose (SUC) on stool output, concentration of the main bacterial populations in stools, and occurrence and severity of intestinal symptoms (flatulence, bloating, abdominal cramps, diarrhoea). Ingestion of GUM 10 and 15 g/day for 10 days increased total lactic

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... g bacteria and bifidobacteria counts in stools, without affecting total anaerobe and aerobe counts. The magnitude of this selective effect was greater in subjects with a low initial faecal concentration of bifidobacteria. Faecal digestibility of GUM was around 95% and its caloric value was estimated to range between 5.5 and 7.7 kJ/g. In addition, stool weight increased 30% because of greater faecal water content. Digestive tolerance of GUM was high and not statistically different from that of SUC up to a daily dose of 30 g. Above this dose, the main complaint was excessive flatulence. However, the mean degree of severity remained mild ( B/1), even at doses /50 g/day. Other intestinal events were rarely reported. Thus GUM is a very well tolerated dietary fibre with bifidogenic properties believed to benefit intestinal health. Key words: acacia gum, prebiotic, soluble fibre, stool output, digestive tolerance. SUBJECTS AND METHODS Substrates GUM (Fibregum † ; Colloids Naturels International, Rouen, France) consists of branched arabino-galactans polymers (92.8% of the dry matter) containing the following sugars (molar percentage in parentheses): galactose (38), arabinose (46), rhamnose (4), glucuronic acid (6.5), methylglucuronic acid (5.5). Its molecular weight is 882 kDa and its polydispersity is 1.74. The effects of GUM were compared with that of sucrose (SUC, placebo), and shortchain fructo-oligosaccharides (FOS; Actilight † , Eridania-ae