Dr. Rosedale Responds To Stephan Guyenet
ertaining to insulin's primary purpose: Again, we must distinguish between controlling blood sugar and lowering blood sugar in a "normal" individual. Yes, I am well aware as are most people, that insulin can lower blood sugar. It does not mean, however, that insulin is controlling it. It is lowering the glucose levels as a side effect secondary to storing it as glycogen (little) and fat (lots), not to control the serum levels as we were typically taught in med school. The immediate regulation of blood glucose is left to epinephrine, norepinephrine, cortisone, glucagon, hGH, all of which control it in an upward direction primarily to make sure there is an anaerobic fuel available for emergencies. Just as we would not send a man to the moon with just one mechanism to deliver O2, we have many mechanisms to increase glucose, not lower it. This may be a very good clue of our evolutionary priorities.
Furthermore, as far as glucose levels are concerned, a major role that insulin plays is to inhibit gluconeogenesis that would otherwise raise glucose by default, as seen in type-1 diabetes, as well as type-2, i.e. why they wake up with high BS even after fasting 10 hours. This may even be more to preserve lean mass than concern about high glucose levels in a normal, non type-1 diabetes individual. Also, I doubt there were enough type-1s in our evolutionary history for nature to give a whit about. Granted, however, that extremely high Blood Sugar leading to spillover in the urine and dehydration as typically seen only in an uncontrolled type-1 diabetes along with severe acidosis would be selected against with relevance determined by the number of these individuals.
Pertaining to all others with elevated glucose; type-2 diabetes, impaired glucose tolerant individuals, anyone shortly after eating a typical breakfast of cereal and orange juice, etc; the chronic diseases associated with this (all the chronic diseases of ageing) including Coronary Artery Disease and cancer afflict most people after having reached reproductive maturity. Even relevant parenting (especially in our ancestral history when reproduction was likely at an earlier age) lies beyond evolutionary selective pressure. Thus elevated glucose would not have had great pressure to be selected against and may even have conferred advantages. type-2 diabetes may therefore be an example of "antagonistic pleiotropy". "Insulin's primary, evolutionary role was established billions of years ago" long before glucose was a significant part of our diet. Insulin is found in virtually all animal life, "down" to worms and yeast (where it also takes on IGF functions). It was certainly not used to lower blood glucose levels. I am also aware of leptin and its role in centrally regulating glucose, insulin, and most of the hypothalamic functions... I have written a book on this.
Pertaining to maintenance and repair: The energy required for basal metabolic rate should almost entirely go to "maintenance and repair" such as the maintenance of body temperature, the maintenance of heart rate, etc. Also, you mention moving muscles. Whenever that is accomplished, it damages the muscle and there must be repair of that muscle. I will quote from the recent article published in the journal Nature out of Linda Partridge's lab that you mentioned: It [calorie restriction] is widely assumed to induce adaptive reallocation of nutrients from reproduction to somatic maintenance, aiding survival of food shortages. -From: "Amino-acid imbalance explains extension of lifespan by dietary restriction in Drosophila", Nature, Dec 2, 2009. That was my assertion...that it is a popular and widely accepted (even "assumed") theory. Reproduction vs. maintenance and repair derives from Tom Kirkwood's very popular "disposable soma" theory... I think that the major point is being missed. I am talking about care and repair of the genome vs. its reproduction. The soma (body) is to take care of the genome until it can be reproduced and until it is environmentally/nutritionally advantageous to do so.
Therefore all energy that goes into maintenance of the soma, whether that be for individual cells (outside of the nucleus) or the body of cells, until the genome can/should be reproduced, is energy for maintenance and repair. This allocation was apparently established during oceanic single celled life billions of years ago. Even so, the fact that M&R and reproduction are linked does not imply that it must be... the fact that it may be possible to unlink them does not mean that they were not linked or are not naturally linked. As far as Kitivans are concerned, one can debate all one wants about what ancient man ate or current societies eat... and it gets you no closer to determining the optimal diet (excepting that they may indicate what not to do). Diets evolved for reproductive success, not long, healthy, post reproductive life... for that we have no footsteps to follow.