Thermic Effect of Food

[Guest guest]

It is (was) my understanding that the thermic effect of digestion of

the various macronutrients is essentially similar with perhaps

slightly more necessary to digest protein. However, I came across this

while reading The National Academies Press, Dietary Reference Intakes

for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol,

Protein, and Amino Acids (Macronutrients) (2005).

They claim the " energy expenditure during digestion above baseline

rates " for protein is up to THREE TIMES more than for carb or fat due

to the amino acids. They give references; the text in question is

below. Does a gram of protein require up to 3X more calories to digest

than for instance a gram of carb? Appreciate any clarification of this.

" It has long been known that food consumption elicits an increase in

energy expenditure (Kleiber, 1975). Originally referred to as the

Specific Dynamic Action (SDA) of food, this phenomenon is now more

commonly referred to as the thermic effect of food (TEF). The

intensity and duration of meal-induced TEF is determined primarily by

the amount and composition of the foods consumed, mainly due to the

metabolic costs incurred in handling and storing ingested nutrients

(Flatt, 1978). Activation of the sympathetic nervous system elicited

by dietary carbohydrate and by sensory stimulation causes an

additional, but modest, increase in energy expenditure (Acheson et

al., 1983). The increments in energy expenditure during digestion

above baseline rates, divided by the energy content of the food

consumed, vary from 5 to 10 percent for carbohydrate, 0 to 5 percent

for fat, and 20 to 30 percent for protein. The high TEF for protein

reflects the relatively high metabolic cost involved in processing the

amino acids yielded by absorption of dietary protein, for protein

synthesis, or for the synthesis of urea and glucose (Flatt, 1978; Nair

et al., 1983). "

http://www.nap.edu/books/0309085373/html/114.html