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Dietary Soybean Protein Compared with Casein Damages Colonic Epithelium and Stimulates Colonic Epithelial Proliferation in Rats^{1, 2,}

Department of Nutrition, Netherlands Institute for Dairy Research (NIZO), P.O. Box 20, 6710 BA Ede, The Netherlands

Recently we showed that soybean protein compared with casein stimulates the fecal excretion of endogenous magnesium. In the present study we investigated whether this differential effect of soybean protein is due to intestinal epithelial cell damage and thus results in a compensating increase in proliferation of epithelial cells. Two groups of six rats were fed purified high fat, low calcium diets, differing only in the type of protein. When compared with casein feeding, soybean protein feeding stimulated the fecal excretion of magnesium, fat and fatty acids, but had no effect on the excretion of bile acids. In fecal water, the concentration of bile acids was lower when soybean protein was fed. In contrast, free fatty acid concentration, as well as luminal cytolytic activity, was higher in fecal water of rats fed soybean protein. Furthermore, epithelial cell damage and proliferation of colonic epithelium (measured as in vivo incorporation of tritiated thymidine into DNA) were greater in rats fed soybean protein. The stimulation of colonic proliferation by soybean protein is consistent with the observed increase in luminal cytolytic activity and epithelial cell damage. We conclude that the stimulatory effect of soybean protein on endogenous magnesium excretion is due to a soybean protein-specific damage of colonic epithelial cells, which results in a compensatory epithelial cell hyperproliferation.

KEY WORDS: • rats • bile acids • fatty acids • soybean protein • colonic proliferation

¹ Supported by grant 900-562-078 of The Netherlands Organization for Scientific Research (NWO), Medical Sciences.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence should be addressed.

Manuscript received 23 February 1993. Revision accepted 2 June 1993.