Thank you for your thoughtful response, DJ Delorie. I appreciate your views.
I've added a few more of mine for your consideration.

"DJ Delorie" wrote in message
...

"John" writes:
The more food energy wasted as heat,

In general, though, that part is the misleading part. The body
regulates waste heat too, to maintain body temperature. So, waste
heat is fairly constant, and thus is not a factor of concern when
trying to figure out what makes a diet work or fail.

Respectfully, I disagree. Waste heat will vary depending on the level of
physical activity and caloric demand by the body. Our body regulates these
fluxuations in wasted heat through perspiration and vascular/capillary
dialation. Exercise not only uses more calories in our muscle tissue but
also more in wasted heat energy due to the increase in overall caloric
demand to fulfill the exercise energy requirement.

My thought is the energy lost in going from carb calories to ATP is
less than the energy lost going from fat calories to ATP.

I don't think this is true. In general, the wasting steps in
metabolism are in the digestion of food, not the burning of it.
Protein, for example, is 5 cal/g in a calorimeter, but only counts as
4 cal/g in food because it costs 1 cal/g to digest it. Google on
"thermic effect of food". Note that fat has the lowest losses here.

Respectfully I disagree. The body is very efficient at storing fat
in adipose tissue, not burning it.

Proof? I say the body can efficiently do either, but whether it
*chooses* to do one or the other varies from person to person in
response to hormonal influences.

I will try and find the articles about efficient fat storing. I believe it's
in this URL: http://www.sportsci.org/encyc/adipose/adipose.html
I agree some individuals do have bodies that prefer fats but I think they're
not the majority. None the less, if we restrict carbs, the body has no
choice and it's forced to use fat. If you accept the premise that as a
result of limited carb intake, "most" bodies will use fat for fuel, our
discussion becomes one of fat to ATP conversion efficiency. In my favor I'd
submit the caloric density of fat would lead one to think an ingested gram
of fat would be more than enough for the body compared to 1 gram of
ingested carbs. If the chemical transformation process for fats to ATP were
as efficient as carbs to ATP, wouldn't we get fatter since our body is
getting twice the available calories? I am assuming we eat to "feel" full
which is a bulk/mass subjective determination that I'm not sure how to
quantify. Do 4 grams of olive oil satisfy one's hunger more or less than an
4 grams of dry rice (subsequently cooked and eaten)? Maybe the amount of fat
in terms of grams ingested is less that the grams of carbohydrates ingested
for the same "feeling" of being full.



My evidence is skinny people. When I was a teen, I could eat
thousands of calories a day and never gained weight (heck, I was
*trying* to gain muscle at least, no luck). If my body were very
efficient at storing fat then, I'd have been fat then. I was burning
fat like crazy. These days it's different. Have the laws of physics
changed? Or just my hormones?

My thought would be that your activity level not only used every carb
ingested but also all the ingested fat. Why one body has a higher "rest"
energy requirement is another discussion. But I would say you had a very
high rest energy requirement and then added physical activity too it. My
guess is when we're young our hormones are doing many crazy things with
weird results.

Are you suggesting the calories listed on food labels are not the
gross caloric content of that food item? I thought food was "burned"
in a test lab to determine it's caloric value.

Yes, I'm saying that. Protein, for example, is 5 cal/g in the lab,
but 4 cal/g on the label. Fat is the same in both because it requires
so little energy to digest and metabolize.

The problems we've seen here is that some people have ABNORMAL
metabolisms - their "thriftiness" is so asymmetrical that the type
of calories they ingest determines whether they're stored or
burned, and how difficult it is to release stored calories later.
For "normal" metabolisms, it doesn't matter what kind of calories
you eat.

If that were true, then the low carb diets would not be working as
well. Fats would come to the rescue in as much as a gram of fat has
about twice the caloric content as a gram of carbohydrate.

Ah, but that's exactly why LC diets DO work well. They address the
problems of the abnormalities, in such a way to work around the
problems and let the body function normally.

And the "gram of fat" part is irrelevent. The body doesn't really
store carbs (just a tiny bit as glycogen), but it readily stores fat.
To compare the two in a diet, it's only the calorie content that
counts, not the mass. Yes, a gram of fat has more calories than a
gram of carbs, but 100 kcals worth of carbs and 100 kcals worth of fat
are the same diet-wise.

However if the body has been calorie-satiated with carbohydrates then the
fat isn't burned at all but stored. Therefore the mass is important until
that fat mass parked in the adipose tissue (in a slightly modified form) is
required for cell fuel.