Fiber digestibility and breath-hydrogen excretion in subjects consuming rural and urban Mexican diets.

Apparent digestibility of dietary fiber and its effect on breath-hydrogen excretion and gastrointestinal symptoms were determined in 16 subjects consuming a plant-based rural Mexican diet (RMD) and a more refined urban Mexican diet (UMD). Neutral-detergent-fiber intake and digestibility were 40.2 and 22.7 g/d (56%) for the RMD and 12.1 and 8.9 g/d (70%), respectively, for the UMD. Apparent digestibilities of hemicellulose, cellulose, and lignin were 40%, 63%, and 53% from the RMD and 73%, 75%, and 58%, respectively, from the UMD. Total breath-hydrogen excretion during 10 postprandial h was similar after both diets, showing that the breath-hydrogen test is of limited value for comparing carbohydrate fermentation from mixed diets. Mouth-to-colon transit time was 5.7 and 6.5 h for the RMD and UMD, respectively (P less than 0.05). There were significantly more gastrointestinal symptoms with the RMD (P less than 0.01); however, neither diet caused symptoms indicative of serious gastrointestinal discomfort.