What Is The Approximate Value For The Thermic Effect Of A 2500 Kcalorie Diet?
The thermic effect of food, also known as dietary-induced thermogenesis (DIT), refers to energy expenditure above and beyond basal metabolic rate (BMR).
The figure below summarizes the components of total daily energy expenditure in humans, which accounts for about 60% to 75% of total daily energy expenditure in sedentary adults; 20% to 30% is attributable to physical activity, and 5% to 15% is due to increased cost of metabolizing food (thermogenesis); the remaining 10%-20% is due to the cost of storing fuel (see also the table below). The factors that determine DIT are not well understood.
One factor is diet composition, which affects the energy required for digestion, absorption, and disposal of nutrients provided by foods. Another factor is the nutrient composition of the diet.
Diet-induced thermogenesis comprises three different components:
The first two are related to the processing of foodstuffs in the digestive system, while the third represents all other effects associated with digesting and metabolizing dietary macronutrients.
At least some of these mechanisms can be controlled voluntarily to a certain degree; however, most of them seem tightly regulated involuntary processes. Diet-induced thermogenesis has been measured in various conditions within 24 hours after consuming a meal. Depending on the meal’s composition, it may be 2 to 3 times higher than the basal metabolic rate.
The thermic effect of food represents energy expenditure above and beyond resting metabolic rate, which is referred to as specific dynamic action (SDA) or dietary-induced thermogenesis (DIT).
The two main components of DIT are protein-induced thermogenesis (PIT), representing energy necessary for digestion, absorption, and disposal of protein-derived metabolites from foods, and carbohydrate-induced thermogenesis, reflecting energy expended as a result of metabolism of carbohydrates biologically related compounds such as organic acids derived from glucose. In addition, there is also fat-induced thermogenesis (FIT) during the digestion and processing of fats in the diet.
As with basal metabolic rate (BMR), the daily energy expenditure for DIT increases with an increase in physical activity and lean body mass. The question as to whether the rise in DIT accompanies the growth of lean body mass has not been fully resolved yet; i.e., does dietary-induced thermogenesis represent a fixed proportion of BMR, or may it vary according to body size and composition?
It appears that fat-free mass and total daily energy expenditure (including both SDA and DIT) are associated with each other. E.g., among obese women, those with higher values of FFM had higher daily energy expenditure than those who were similarly obese but had lower FFM .
This association between fat-free mass and daily energy expenditure is attributed to the contribution of lean tissues to the maintenance of basal metabolic rate. In addition, following weight loss in obese women, DIT was not changed while SDA was substantially reduced.
Whether a reduction in FFM could explain this finding during weight loss has been questioned and may suggest that compensatory changes in DIT take place and offset the decrease in SDA associated with weight loss.