being confused is good... it means you're at least searching for understanding in a sea of information.
Keep in mind that the whole debate over "a calorie is a calorie" depends on how you want to frame this statement:
- biochemically, this rule holds: because it simply states the first law of thermodynamics. it cannot be violated. (a calorie is a calorie) equations on paper will always work out... This was the beef Buchholz had with Fine and Feinman, their theory is quite solid... but
- empirically, the rule "fails": because of the second law of thermodynamics says that entropy will parasitize the system; and it does. ( 1 calorie in = 0.8 calorie out or worse). protein is more thermogenic than fat and glucose for well-known reasons. also, hormonal variations will affect mechanical and chemical extraction efficiencies so that some folks will make better use of their intake (those tending towards weight gain) and others will not (skinny folks). Those tending towards weight gain are Priuses (45 mpg) and those who remain skinny are like Mack Trucks (5 mpg)...see the chart I made (there's a link at the bottom of this post) for an estimate.
Entropy is not the only reason for the difference, though. There is an even greater factor that Buchholz did not address:
humans are not JUST biochemical machines 
.
if we were, the question of dieting would not exist.
Humans gain weight mostly due to intake and secondarily due to indolence.
let me repeat: humans gain weight
mostly due to intake and secondarily due to
indolence.
But the folks who only look at biochemistry already know that. the problem is they keep their thinking on a biochemical level and simply assume that "putting the fork down" or "moving your behind" is the solution. If we were machines (like your car), it would be.
Sadly, we are powerfully attracted to
sweet,
fatty,
salty, and
soft foods because these foods are more likely to be energy dense and easy to eat, and this feeds a need that has been hard-wired into our evolved bodies over hundreds of millions of years! for 99.99999% of our evolutionary history (way back to the first tetrapods), sweet, fatty, salty, and soft foods were rare so that nature limited our access to them... as such, we developed a "bloodhound nose" for anything that might have these traits: I can smell baking bread a mile away! Today such foods are plentiful and cheap, but our hormones are still wired to assume such occurrences are rare and so when we come across them, we gorge ourselves.
our hormones are well adapted to detecting such foods, but poorly adapted to regulating our intake:
if for 99.99999% of our evolutionary history nature limited our intake of such foods, why would our bodies need to evolve regulatory mechanisms to limit our intake of such foods? (ok, we need some, but not much). This also explains why humans lost the ability to synthesize ascorbic acid while other mammals can: because primates ate plenty of fruits such that the loss of gulonolactone oxidase (the final Vitamin C synthesis enzyme) was not a problem; we got more than enough vitamin C from nature. the moral: why make enzymes to regulate something when nature provides the regulation for you (positive or negative)?
This explains why for many of us, food is more than just a fuel... it's a love affair.
- It's an addiction: many people who give up carbohydrates will go into withdrawal symptoms vaguely resembling alcohol and opiate withdrawal. When I gave them up for the first time, I couldn't get out of bed for 2 days!
- It's a constant temptation: those who don't have it, can't understand how the refrigerator "calls" you at 2 am in the morning, especially when you have sweet, salty, soft, and fatty things in it!
- It's a social tool: few folks take their girl to eat salads, we take her to eat burritos, big steaks, funnel cakes, nachos, and other sinful foods. So many social occasions center around foods, and we never give a thought to healthiness... it's all about tastiness baby!
- It's medication: girls aren't the only ones who eat food when sad, we do it too. we also eat when bored, tired, and happy. and it treats our emotions to some extent.
With so many emotional reasons and the ubiquity of food and sources of it, calorie maintenance becomes, NOT a matter of calories in, calories out, but of
understanding its impact on your behavior (e.g., you're not a robot):
The positive (negative) feedback loop: This poor regulation of food first leads to weight gain and
that weight gain results in hormone imbalances that are even
more conducive to weight gain: getting fat makes it easier for you to get fatter for two reasons:
- The food's drug-like addiction: most sweet and processed foods have opiate-like qualities. giving them up will affect your brain's chemistry in the same way so that you will hate life until you either get over sweet food long enough, or give in and gorge on your addiction again.
- The hormonal imbalance favors food storage & energy efficiency: your growing fat cells, in the presence of sweet foods will grow and actually increase insulin resistance and reduce satiety signals. this dysregulation will mean more of the food you eat goes to your fat cells (adipocytes) and less of it feeds your body (muscles and organs). your body is starving, so it keeps you hungry, but sadly, you never quite feed it since most food (thanks to your poor hormones) is getting shunted to your adipocytes. your body is more efficient than ever and you're hungrier than ever...
In such an imbalanced environment, is it any wonder that dieting is such a Sisyphean task, almost always doomed to fail?
Not convinced? go look up the failure rates for dieters and compare them to the failure rates for alcoholics and opiate addicts. hint: they're all more or less the same!
This human behavioral aspect is conveniently overlooked in most diets and studies on diets, yet it more than accounts for the difference in diet effectiveness for a few reasons:
- People lie on studies: the more regulated they are, the less likely this is to happen, but even in metabolic chambers, people sneak snacks in many ways. Just ask anyone sent to a fat camp if cheating occurred...
- People lie during diets: addiction is such a terrible mistress... we lie for our addiction, we cheat for it, and we steal for it if necessary. it may not be as bad as heroin, but we know from studies that the same mechanisms are at work, it's just a matter of degree.
- Your body lies to you: the fact your muscles are starving while your adipocytes are growing throws off your sense of reality so you feel hungrier, you're getting fatter, but some part of you is really getting smaller (your muscles and organs). your world is topsy turvy and even if you're 100% honest to others, your perception of reality will lead you to eat the wrong amounts of food and to report less than what you ate because you honestly only saw a tiny plate of food and not a heaping mountain of it!
in short, the behavioral effects of certain foods, particularly sweet and soft foods (junk foods) affects more than our biochemistry. studies that try to control for this may only report the biochemical effects of food, but food is not gasoline... it's tasty, delicious, and we'd do so much for it!
And there IS a biochemical advantage to low carbohydrate diets, we know this from theory and from empirical research (see the 2012 JAMA article in a previous post, 2004 Buchholz, 2004 Volek, 2007 Gardner below and pay close attention to the results in their tables). It's just that this effect is often overwhelmed by our behavioral effects, both in the short term (cheating, lying) and in the long term (hormonal dysregulation, insulin resistance).
Finally, to be fair, human variation dictates that some of us will have adequate regulation, either due to tight biochemical or hormonal control, poor access to junk food, or being too busy to indulge. These are the folks we love to hate because they are naturally skinny for many such reasons that we wish we had.sources:
- https://docs.google.com/open?id=0B05o7uyVl6paNkxzdF9OUTZOM00 (read my notes on this paper) also, read the studies in Table 1, her own journal recognizes that low carb diets burn more calories, just not at the massive levels some would like.
- 2004 ACJN Letters to the Editor the discussion over the 2004 Buchholz paper that bohm2 refers to
- https://docs.google.com/open?id=0B05o7uyVl6paQ0pnYThQcmk0eDA An early paper that also showed the clear metabolic advantage
- https://docs.google.com/open?id=0B05o7uyVl6paUkJEdEgwMm5mMG8 This paper stirred up a hornets nest among dietitians, but has stood the test of time.
- 2008 Avena: Evidence for sugar addiction behavior
- https://docs.google.com/open?id=0B05o7uyVl6paVVExOUx2eFdjT1k
- https://docs.google.com/open?id=0B05o7uyVl6pab09jRWczNXFqeG8