kcal may still be a kcal when verified in a bomb calorimeter - I believe for food they do it the same way everyone else does it: Put it in pure oxygen atmosphere, and light that baby on fire, measure the increase in temperature in a controlled environment, and the 'heat' produced is expressed in kcal.

now, my body does not have an active flame, and I don't have a combustion engine in my stomach. I use a (mysterious to me) metabolic process to convert what I eat into energy that my body can use.

For me, an individuals metabolic rate may be roughly proportional to kcal intake, but it is not the same thing, and it is different for different food types, combinations, and for different people.

I liked the article - even though I am not a dietician, I do think there is something wrong about the Adkins diet.. not healthy.

You are right that you have to adjust for metabolic rate; and while the content of your diet will have an effect on that rate (meaning getting an entirely accurate assessment of your expenditure is near impossible) the kcal value maintains;

I suppose it's my mentality that you adjust your eating habits based on your diet contents and its effect on metabolism, to match the kcal values, rather than viewing the kcal as an inconstant value.

Thank you, by the way. I enjoyed the opportunity to think though this

This dialog reminded me of a rumor I heard awhile ago about trying to measuring efficiency of Lance Armstrong (competitive cyclist). A brief search gave me [1], but I'm sure there are better articles out there. My big take away is that even with modern technology and understanding there is just so much we still don't fully understand - especially about the human body and processes.

[1] http://www.sportsscientists.com/2008/09/coyle-and-armstrong-...

Actually, no. Here's an article that explains why this is not the case:

http://garytaubes.com/2010/12/inanity-of-overeating/

While an interesting read, it feels like I just read some long winded analogy describing metabolism?

In the parent comment, I'm including bodily factors like metabolic reactions within "expend". The degree to which this makes a difference in overall expenditure is the un-quantifiable part; but adjusting your diet further to counter this lack of expenditure will still have the same effect. It still is a numbers game in my mind.

I see this reaction all the time:

"A calorie is a calorie is a calorie. If you want to lose weight, you just need to eat less."

"Well, no, your body can react differently to different types of calories. If some calories tend to induce hunger and others don't, then it matters quite a lot which calories you consume."

"Well, yeah, sure, everybody knows that."

Well, no, everybody may "know" it, but when you're not looking, they'll slip "a calorie is a calorie" right back in.

This matters. Either eating certain foods induces more calories to be consumed, in which case the key to dieting is to eat certain foods and not eat others and decades of consensus and advice are irredeemably, irretrievably wrong, or a calorie is a calorie and these sorts of studies are irredeemably, irretrievably wrong (as this is hardly the first one to suggest lower carb or lower GI diets are superior). Some people seem very comfortable just sort of sliding into the "sure, calorie type matters" whenever it is argued, but somehow not being willing to follow the logic that if calorie type matters, then certain further research and conclusions are called for that are sharply at odds with conventional wisdom, which has been very, very much that a calorie is a calorie is a calorie when it comes to weight gain.

Conventional wisdom and decades of dieting advice have been deeply, profoundly, foundationally based on a calorie being a calorie being a calorie, and if that is not true, the conventional wisdom is deeply, profoundly, foundationally if you like, flawed. There's no two ways around this.

(Though I absolutely, positively guarantee that if it does turn out that calorie type matters that this move will be used to slowly but surely rewrite the last 50 years of dietary history such that the conventional wisdom was always right and never said anything about calorie types not mattering. But it won't be true.)

The trouble is that your digestive process isn't necessarily time-independent, so the same piece of food could represent different energy fluxes into your body if eaten at different times, and the calorie expenditure of your body isn't necessarily time-independent, so the same exercise (including just sitting around) could represent different energy fluxes out of your body if performed at different times.

Without actually measuring energy fluxes, "a kcal is a kcal" is meaningless.

The point of the original study was: 1) For weight loss, how many calories you eat (or don't eat) matters more than any other factor. 2) Once the weight loss period has ended, the type of diet (i.e., the balance of calorie types consumed) matters more for maintaining the new weight and overall health.