| Summary: | Animals can associate orosensory characteristics from food with postingestive effects and adjust meal size to prevent energy deficit. By using odor-fasting duration conditioning, two studies were conducted to test the above hypothesis. In the first study, thirteen male and eleven female adult Wistar rats were given 1.5 hours to ingest a casein-based test-meal odorized by either vanilla or chicken flavor prior to a 4-hour short-fast or a 12-hour long-fast. Rats went through the training phase with a pseudo-random sequence of six duplicates of each odor-fasting pairing over four experimental days, followed by an odor preference test. Gender differences may exist regarding hunger perception because only females were capable of adjusting meal size according to the postprandial fast duration. A second study was conducted to examine whether a sugar-rich meal can improve acquisition of anticipatory satiety through memory enhancement. Thirty-two female Sprague-Dawley rats were given either a sugar-rich or a protein-rich test-meal prior to the post-prandial fasts. Rats were conditioned in a similar fashion to the first study except that different odors were used, postprandial fasts were shortened to 3 and 10 hours, whereas training phase was elongated to eleven duplicates and followed by an extinction phase. Both dietary groups acquired the anticipatory satiety. However, probably due to the carbohydrate-induced overeating, the sugar-rich group in contrast to the protein-rich group, exhibited a delayed learning in meal-size adjustment prior to a short fast. The above studies demonstrated the existence of gender and macronutrient differences in food intake regulation.
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