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Digestion and Passage Kinetics of Chimpanzees Fed High and Low Fiber Diets and Comparison with Human Data^1,2,

Department of Anthropology, University of California, Berkeley, CA 94720 ^* Department of Agronomy and Range Science, University of California, Davis, CA 95616

To investigate the digestive kinetics and fiber digestion of great apes, we conducted digestion trials on chimpanzees (Pan troglodytes) with diets of two fiber levels, one containing 34% neutral detergent fiber (NDF) and the other 14% NDF. Chimpanzees exhibited a response to fiber similar to that of humans. First, increases in the fiber concentration of the diet decreased mean transit time (MTT), hindgut turnover time (T) and the digestibility of fiber. Second, differences in MTT and T between the treatments and animals explained most of the variability in the digestibility of fiber components. Third, consistent with human data, the fiber marker passed more slowly than the liquid marker only when the high fiber diet was consumed. Fourth, individual variability, as in humans, was a significant factor affecting digestion and passage. Fifth, the MTT of chimpanzees was longer than that of humans. This result may be due to the apes' larger hindgut. In comparison with other hominoids, humans have smaller volumes in the gastrointestinal tract and hindgut. The gut proportions of modern humans, in combination with evidence from the fossil record, indicate that during its evolution the human lineage was able to overcome nutritional constraints imposed on body size increases in the great apes. We suggest that this advance was achieved through technological and social innovations that permitted early humans to achieve larger body size without lowering dietary quality.

KEY WORDS: • digestion • kinetics • fiber • chimpanzees • humans • human evolution

¹ Research was funded by a grant from the Wenner-Gren Foundation for Anthropological Research. The Foundation for Research Into the Origin of Man (F.R.O.M.) aided with funding for formulation of trial diets.

² K. M. and M. D. were temporarily affiliated with the Yerkes Regional Primate Research Center, Emory University, Atlanta, GA 30322, to carry out feeding trials. The Yerkes Center is supported by Base Grant No. RR-00165, Animal Resources Program, from the National Science Foundation and is fully accredited by American Association for Accreditation of Laboratory Animal Care (AAALAC).

Manuscript received 6 November 1987. Revision accepted 8 March 1988.