Egg yolk protein improves loperamide-induced constipation and cecal fermentation in rats

Constipation is a risk factor of colorectal cancer. Phosvitin in egg yolk proteins is resistant to proteolytic action and has a high content of serine that may be associated with its high water-retaining capacity. The aim of this study was to evaluate the effect of egg yolk protein on constipation and cecal fermentation in a rat constipation model. Male Wistar rats were fed a purified AIN-93G diet containing either 20% casein (control) or 20% egg yolk protein for 14 days. Constipation was induced by administration of loperamide (5 mg/kg body weight/d) for the final 5 days of the experiment. The number and dry weight of feces in rats fed yolk protein were higher than those in the controls. Cecal acetate, propionate, and n-butyrate concentrations were higher in rats fed yolk protein than in the controls. Fecal nitrogen content was significantly higher in rats fed yolk protein. In the feces of the yolk protein group, serine comprised more than 40% of the amino acids. These results indicate that egg yolk protein consumption suppressed loperamide-induced constipation in rats because serine-rich protein phosvitin in yolk proteins might be resistant to digestion in vivo.