We have previously reported that a soy oil-containing experimental diet (fat-free AIN93G containing oil thermally processed with soybean protein followed by filtration), inhibited body weight increases without any adverse effects when given ad libitum
to male Wistar rats for 12 weeks. In the present paper, the mechanism of weight-loss promoting effects was investigated. Fasted 10-week-old rats were fed a slurry composed of AIN93G (fat-free), Cr2
(marker), water, and 7 wt% soy oil or fresh oil (control) and sacrificed at 20, 60, 90, 120, 150, 210, 270 or 360 min. The stomach, small intestine, cecum, colon and feces were then collected to determine the distribution of the slurry in the digestive tract. The results indicated that the content was transferred faster from stomach to small intestine in the soy oil group than in the control group. Fecal excretion (derived from a commercial standard diet ingested before slurry administration) in the soy oil group was significantly higher than in the control group. Digestive enzyme activities, lipase, sucrose, and maltose, were not inhibited by soy oil. In addition, feces collected in the 12-week feeding experiment were more in the dry weight and contained higher levels of nitrogen and water in the soy oil group than in the control group, revealing that an increased amount of nutrition was continuously excreted in the former group. The above-described findings suggest that soy oil stimulated peristalsis of the gastrointestinal tract and that colon contents are actively excreted, resulting in safe and steady body weight decreases.
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