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Introduction The structure of a circadian rhythm depends on the activity of the suprachiasmatic clock, on the presence of zeigebers, and on the presence of masking factors. Regarding body temperature, a clear circadian rhythm is well recognized, with maximal values approaching dusk and minimal in the small hours, near dawn. However, masking factors can enhance or reduce the amplitude of the circadian rhythms. Food eating is a masking factor on the body temperature rhythm, probably related to the Thermal Effect of Food (TEF), a measure of the energy spent for the digestion, absorption, and disposal of a given amount and type of food. Also, the Glycemic Index (GI) shows how quickly blood glucose rises after eating a given amount and type of food. As high GI foods require lower digestive processing, their TEF should be lower than that of lower GI. The present study aims at recording the consequences of modifying the GI of a mid morning snack on the whole 24 h body temperature cycle in young human subjects. Materials and methods The study was conducted on 15 university students (8 female, 7 male, 19–25 years old). Each subject was provided with an activity meter and a wrist temperature holder during two non consecutive periods of 5 days. During the experimental days, each subject ingested between 10.30–11.30 AM one of two snacks of precise composition with low and high GI. Each participant was blind to the GI of the snack ingested. Results Significant differences were found between the averaged peripheral temperature of the subjects during light and dark periods. Also, the 2nd harmonic component (12 h) was modified. From the well known phase opposition between central and peripheral temperature, the results point to changes in the central temperature cycle. Arguably, TEF dependent changes in the peripheral dissipation could occur without real changes in the core temperature. However, the TEF consequences does not extend beyond 6 h after ingestion, while the recorded changes in peripheral temperature showed long term effects, being extended up to the whole 24 h cycle. Therefore, the body temperature seems to have been modified as a consequence of the nutritional properties of a small mid morning snack. Conclusion The body temperature cycle shows a high sensitivity to the GI of a minor meal. |
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