Effect of high crude fiber intake on transit time and the absorption of nutrients in South African Negro schoolchildren.

Transit time (using carmine as marker) averaged about 9.5 hours in rural South African Negro children aged 9-12 years, when ingesting a mean of 10 g crude fiber per diem on their everyday diet. A: in subgroups of 40-50 pupils, supplements of maize and wheat bran, and of wholemeal bread--each affording about 2 g fiber--also of oranges, affording 4 g fiber, decreased transit time only slightly, to about 8.5 hours. Hence, pupils current daily fiber intake, in its effect on transit time, is already acting maximally. B: mean respective fecal nitrogen and fat concentrations on everyday diet were not significantly affected when the subgroups ate one of the following fibre-free foods: 1) 40 g protein from skim milk; 2) 40 g fat from butter; 3) 40 g carbohydrate afforded by sugar. Additionally, on their usual diet, also following the ingestion of 40 g uncooked maize flour, starch was extremely seldom detected in feces. C. feces collections for 5-day periods were made on small groups of pupils (8 per group) when consuming first their everyday diet, and next when including each day one of the following: 1) 40 g protein from skim milk; 2) 40 g fat from butter; 3) 40 g sugar. On these regimens, there were no significant changes, compared with respective data on everyday diet, in mean amount of dry feces excreted daily, in concentrations of nitrogen and fat, nor in amounts of nitrogen and fat excreted daily. Yet a daily supplement of 350 g oranges (5-7 oranges), although virtually nitrogen- and fat-free but containing 4 g fiber, resulted in slightly shorter transit time but highly significant increases in mean amounts of dry feces, nitrogen and fat excreted daily. Observations suggest that the protein, fat and carbohydrate (excluding unassimilable fiber) in the supplements were virtually fully digested and absorbed. Discussion suggests that this also applied to nutrients in the everyday diet. It is judged that the large stools voided by these people (and others consuming diets high in fiber) are composed, apart from unassimilable fiber, almost wholly of endogenous products.