Re^2: Poster 623 answer!?
Dr. Riddle: Thanx for the detailed response. The fact that the energy required for the absorption process is so small compared to overall expenditure would make it meaningless to measure it. What about the energy efficiency?
On Tue Dec 8, mike riddell wrote
>On Sat Dec 5, grover wrote
>>Dr. Riddle: Fascinating results. Hope you are having fun at the meeting. I was wondering whether your energy calculations take into consideration that glucose absorption itself requires energy and whether the efficiency of energy release from the two pathways are identical.
>Dear Dr. Grover,
>Thank you for your interest in the study. You asked a very thought provoking question that I must admit I had not yet considered. Our estimation of energy expenditure (indirect calorimetry techniques) during exercise would not be able to detect the small increase in energy expenditure from the assimilation of the glucose. A few points are worth mentioning, however;
>1) The thermic effect of a mixed meal of carbohydrate, fat and protein is about 10-15% above the resting energy expenditure and includes obligatory thermogeneses (absorption, breakdown, and storage of nutrients) and facultative thermogeneses (activation of the sympathetic nervous systems). During exercise, the percent increase above the metabolic rate would be substantially less, and again, probably not measurable with our techniques.
>2) In addition, for glucose provided in a solution, as in this experiment, the increase in energy expenditure would be much lower than a mixed meal because of its simple composition (less digestive processes, facilitated glucose absorption, etc.). Further, It is estimated that if the glucose is oxidized (i.e. during exercise) and not stored as glycogen, then only about 7% of the total available energy from glucose is lost to thermogeneses (Flatt JP, 1987, Am J Clin Nutr, 45:296-306).
>3) To determine the thermic effect of feeding glucose vs water in our study, we could make VO2 comparisons in the resting state with both water and glucose intake trials over a 1-2 hour collection period. We may be able to detect a difference in VO2. I’m not sure if this would be a valid correction for our study, however, since exercise would have a different SNS stimuli and the destination of the glucose would be much different, thereby, possibly affecting the energy cost.
>Thanks again for the question,
>Any thoughts on this discussion, or other points related to our study are appreciated!
Tue Dec 8