----- [log in to unmask] wrote: 
> I was reading Dr. Eades' excellent blog entry today on Taubes' new 
> book 
> (http://www.proteinpower.com/drmike/low-carb-library/why-we-get-fat/) 
> and even he claims that the body is a closed system with respect to 
> calories. Two reasons why this may not be so: 
> 
> 1) Calories are measured with a bomb calorimeter. The body may not 
> "burn" food the same way this instrument does. 
> 
> 2) The calories in, calories out formula never takes into 
> consideration calories *excreted." 

Gary Taubes's new book is worth reading, by the way. 

The body is not a bomb calorimeter, but the "burning" of fuels does much the same thing, which is to release the energy stored in chemical bonds. Our bodies are indeed very good at this. Of course, total caloric content of a food includes indigestible fiber, which has to be subtracted to get the "available" energy. 

I don't think we excrete a lot of calories. For good reasons, our bodies don't tend to throw fuel overboard. There is no doubt that we excrete some, however. Fecal fat is sometimes measured to test whether the intestines, liver, pancreas, etc. are working properly. Normal fecal fat is 7 g/day. 

In ketosis, various kinds of ketones are produced. One of them, acetaldehyde, is toxic and must be excreted, so it is typically dumped into the urine or sweat. In so-called "deep" ketosis, ketones are produced in large enough quantities that even usable ones are excreted in the same way. They are volatile, so if blood ketone levels are increased, they simply spill out of the body. That's one part of the so-called Atkins "metabolic advantage." It's not a lot of calories, though. 

Our bodies aren't designed to throw fuel overboard because in an evolutionary context there should be no need to do so. What would be the point? This is what appetite regulation is for. If fuel is not needed, the simplest thing is to stop eating. When everything is working as it should, appetite, eating behavior, body composition, metabolic rate, and activity levels are all seamlessly linked. 

For those of us who struggle with weight problems, perhaps the most maddening thing is to feel nagging hunger when it's obvious that we have all the fuel we need right there where we can see it. Why do we feel hungry? As Taubes carefully points out, obesity is a sign of disordered fat cell metabolism. The fat is there in the fat cells, but the cells that need it for energy aren't getting it. Their "hunger" becomes our hunger. Why aren't they getting it? Because the fat cells aren't releasing it, or at least not at the rate at which the cells are demanding it. In most cases some fat is getting out, but it's happening very slowly, so we get hungier and hungrier. As we all know, the reason why the fat isn't getting out is that insulin, which controls the rate at which fat enters and leaves fat cells, is too high. It's a bit more complicated than that, since lipoprotein lipase and hormone-sensitive lipase are directly involved in the gatekeeping, but insulin controls them. 

What happens if you eat less fuel than your cells need? In a healthy person, the fat cells will readily release stored fuel. You will lose some body fat, and at some point hunger will begin to increase. Your activity levels and metabolic rate will be only slightly affected, for a good while anyway. If your insulin is elevated, due to insulin resistance, the fat cells won't release nearly as much fuel as is needed, so your hunger will be much sharper, much sooner. Your body will begin to try to compensate for the reduction by reducing demand. This involves lowering metabolic rate, so your body temperature will start to drop. Your activity level will drop; you'll become lethargic. You will lose some fat, but because not enough can be released, you'll cannibalize lean tissue as well, so you'll get weaker. 

If a healthy person eats more than what the cells need, the body will perceive this as an opportunity to be active and to promote growth. At certain times of year, for certain periods of time, it will store some as fat, too. But in general, under these circumstances appetite diminishes and the tendency to eat more than what is needed is extinguished. There is no need to excrete fuel. 

The point is that the amount of energy consumed does have an effect on fat storage. The entire apparatus of fat storage would make no sense if it didn't. It just doesn't have the intended/expected effect in people with chronically elevated insulin. 

The trouble with the "simple caloric calculus" isn't that it doesn't take excreted calories into consideration, or that the laws of thermodynamics don't apply. It's that "calories in" and "calories out" are, as Taubes emphasize, dependent variables . This makes the relation between the two non-linear, but still intelligible. 

Todd