Abstract
It is a well-known fact as the specific dynamic action (SDA) that ingestion of foods causes an increased energy consumption, however, its mechanisms and extents of energy wastage have not been clearly decided. Thus, a series of investigations to elucidate the characteristics of SDA were carried out on normal human subjects. Usual procedures for determining SDA are based on subtracting the basal metabolic rate (BMR) from the increased energy expenditures at rest lasted for 6 or more hours after meal. However, it is not reasonable to use the BMR as a base value of minimum energy consumption over several hours because it varies diurnally. Thus, considering the circadian rhythm of minimum oxygen consumption at rest, a new base line was set up according to the following manner. After measuring the BMR at 7: 00, subjects were fed a high carbohydrate diet containing 450kcal and energy expenditures at rest were determined at 14: 00, 15: 00 and 16: 00, respectively. Average of these three determinations was taken as the peak value in the circadian variation at 15: 00. Resting energy consumption at 22: 00 was considered to be equal to the BMR. A new base line was tentatively proposed by connecting three points (BMR at 7: 00, peak value at 15: 00 and value equal to BMR at 22: 00) . Using two base lines (BMR and newly established line) SDA and corrected SDA of standard diets, in which fuel values were changed every 500kcal from 500kcal to 2, 500kcal, were calculated, respectively. In all diets tested, the corrected SDAs were 15% to 20% low as compared with the SDAs, due to the adoption of a new base line. Both the corrected SDA and SDA decreased with the increase in dietary energy. Percentages of the corrected SDA and SDA to the dietary energy were 11.2%, 13.9% for 500kcal; 8.8%, 10.6% for 1, 000kcal; 7.2%, 8.5% for 1, 500kcal; 6.9%, 7.8% for 2, 000kcal; and 5.7%, 6.8% for 2, 500kcal, respectively. Effects of meal frequency on luxurious heat of diet containing 1, 500kcal were examined in four subjects who received the diet once, twice or thrice a day. Results showed that the more frequently subjects took a given diet, the more the wastage of dietary energy increased, suggesting an increased lipogenesis occurred in meal-fed animals.
