I finally got an e-mail answer back (at least on the subject of ATP, but not regarding insulin)... here is the e-mail I received:
Q: I am a bit confused about the distinction between the ATP that can be produced from a gram of stored body fat versus the ATP that can be produced from a gram of stored carbohydrate. You have written that a gram of fat produces 3 x the ATP that can be produced from a gram of carbohydrate. I researched the issue in some biochemistry textbooks and discovered that a Mole of glycogen produces 0.20 Moles of ATP, and a Mole of stored body fat produces 0.49 Moles of ATP. The ratio between these two (~2.5) is almost identical to the ratio between the calories contained in a gram of carbohydrate versus a gram of fat (when using that actual amount of calories contained in each and not the approximation of 4 and 9 that we actually use). So, unless I am missing something, aren't calories derived from carbs and fats in our food an almost exact approximation of how much ATP can be generated from them?
A: The conversion of dietary calories into ATP is complex and never 100 percent of the theoretical conversion of dietary calories into an equivalent amount of chemical energy. Under ideal conditions, one molecule of glucose can make 36 molecules of ATP. Under less than ideal conditions, it can drop to as low as 2 molecules of ATP. One molecule of fat can make 108 molecules of ATP. This is because most of the ATP conversion takes place in the mitochondria and is dependent on the number of two-carbon fragments that previously entered into the Krebs cycle. Since a fatty acid has 9 two-carbon fragments versus 3 two-carbon fragments in the glucose, you can make a lot more ATP from fats versus carbohydrates under even the most ideal conditions. Even when you take into account the differences in calories, a calorie of fat will make 33 percent more ATP than a gram of carbohydrate.
This is basically what was written by Dr. Sears. Of course, this appears to be slightly in error, since a gram of carbohydrate is actually less than 4 Calories and a gram of fat is actually more than 9 calories. But, if this response is accurate, that means that the ATP production from stored body fat is approximately 20% higher than the ATP production from stored carbohydrate under the same conditions.
As I mentioned above, this may mean a slight reduction in the calories required on a daily basis from the various calculators out there is one is filling in missing calories from fat instead of carbohydrates, but it still means that extra calories have to come from somewhere.
For example, most calculators out there put my daily caloric requirements at 3,200 calories. Assuming for the sake of argument that this number is arrived at based on carbohydrates entirely (which I am not entirely convinced it is), that would mean I would get the equivalent amount of ATP from fat by consuming slightly less than 2,700 calories worth of fat.
But, to complicate matters more, no one is eating a 100% fat or 100% carb diet. Even under the basic Zone diet (no 40-30-30), a full 70% of my daily calories are coming from non-fat sources. Protein is a very inefficient source of ATP, and carbs apparently produce about 20% less ATP than fat. So this lead me to believe my actual maintenance caloric needs are still higher than 2,700 calories per day. Under a 40-30-30 approach, consuming 1g of protein per lb of LBM, I end up eating just under 2,000 calories per day. But my short-fall is still greater than 700 calories per day because 70% of those calories are from proteins and carbohydrates (which are less efficient energy sources). I am no mathematician, but it seems pretty clear to me, that I will still need to fill those extra energy requirements. I don't have figures on the ATP that can be produced from protein (and frankly, protein is only used as a source of energy when there aren't enough fats or carbohydrates to meet energy requirements), but, even assuming we use the 1.2:1 number that means the 2,700 caloric requirement number has to be adjusted back up to account for the fact that 1,400 of my calories are from non-fat sources. These 1,400 non-fat calories would (adjusting for ATP) would leave me with about a 200 calorie shortfall. So that means that my caloric requirements would need to be adjusted back up again to about 2,900 calories. And when you factor in that protein is a far less efficient source of energy than either carbs or fat, obviously, the numbers would have to be adjusted upwards again.
Under a traditional model of calculating my caloric needs (i.e., using the calculators), I would need an additional 1,200 calories. Assuming the ATP production of fat to carbohydrate is 1.2:1 (which is more accurate than the 1.33:1 number given above accounting for the actual calories contained in carbs versus fat, not their approximate numbers) and assuming that the caloric requirement calculators are based on carbohydrates (an assumption I am not sure is valid), also assuming that protein isn't being used for energy requirements, but rather all my energy requirement are being met by carbohydrate and fat sources, if I want to fill my additional caloric requirements with fat only, that would mean eating an additional 1,000 calories of fat per day (1,200/1.2), meaning a total daily caloric consumption of 3,000 calories. This would break down to about 600 calories from protein, 800 calories from carbohydrate, and 1,600 calories from fat. The percentage would be p20% c26.7% f53.3%.
Given the number of scientific studies out there showing that carbohydrate consumption that low negatively impacts the performance of athletes, I have to question, even if the ATP figures are correct, whether there are other factors that are coming into play outside of ATP that are more important. Now, my actual strategy is to consume 1.5g of protein and 2.0g carbs per lb. Admittedly, I do this more by the eye-ball method, but this equates more along the lines of 900-1,000 calories from protein and 1,200-1,400 calories from carbohydrate. The remaining caloric requirements end up being filled by fat. Interestingly, this approach get me back to approximately 40:30:30.
Perhaps I eat more calories doing it this way than I would need if I were eating the additional energy in the form of fat, but I am fairly convinced that I benefit from the higher amount of protein and carbohydrates in my diet.
Anyway, I am still waiting to hear back about my questions regarding exercise nutrition and insulin.