Effect of Food, Climate and Exercise on Rectal Temperature During the Day

¹ From the Physiology Branch, Environmental Protection Research Division, Quartermaster Research and Engineering Center, Natick, Massachusetts, and Medical Nutrition Laboratory, Denver, Colorado

A series of experiments were performed to determine the effect of climate, food intake and activity level on the diurnal pattern of rectal temperature (T_r) from 8 a.m. to 8 p.m. The results indicate that living in diverse climates has little or no effect on the diurnal pattern of T_r. Activity level, when food intake was adequate, did not alter the pattern. Fasting, with no exercise, reduced the diurnal elevation to one-half the ‘normal’ elevation. During fasting with exercise the rectal temperature at 8 p.m. was the same as the value at 8 a.m. (i.e. no diurnal increase was evident). Thus, the major portion of the diurnal change occurring between 8 a.m. and 8 p.m. was associated with the ingestion of food.