Relationship between dietary fiber levels and protein digestibility in selected foods as determined in rats.

Samples of 15 food products and feces obtained by feeding them to rats were analysed for dietary fiber fractions. The food products were added as the sole source of protein in 8% protein diets, making up 8.8-51.6% of the diets. Diets were supplemented with 0.54-5.00% purified cellulose to make them more comparable in total fiber. Fiber analyses of food products revealed that the protein sources provided 0.06-7.27% total dietary fiber. The true protein digestibility in rats was negatively correlated with the total food fiber level (r = -0.69, P less than 0.01) or with the food cellulose level (r = -0.82, P less than 0.01) but it was positively correlated (r = +0.81, P less than 0.01) with the purified cellulose level. No relationship was found between protein digestibility and fiber fermentability. Results indicate that several food fiber fractions and possibly associated substances influenced protein digestibility. Purified cellulose did not have the same physiological behavior as food cellulose from the viewpoint of protein digestibility and fiber fermentability.