The Facts about Fat: Finally an Explanation That's Not Just "Calories Count."
The facts about fat that we've all been taught by our public health authorities presuppose that overeating and/or lack of physical activity cause weight gain. As obvious as this idea sounds, it has numerous flaws. Indeed, this entire site is dedicated to eviscerating that idea, which is technically known as the Caloric Balance Hypothesis.
The alterative hypothesis about why we get fat, the Lipophilia Hypothesis, resolves many of the paradoxes that befuddle modern obesity research.
For instance, Lipophilia explains why we accumulate fat in the places we do. Why men get beer bellies and women get fat thighs. Why people get chunky cheeks, double chins, and flabby arms, but they don't accumulate fat on their ears, tongues, or kneecaps, except perhaps under very unusual circumstances.
For an exhaustive discussion of the facts about fat -- how calories 'turn into' adipose tissue -- read chapters 20 to 23 in Good Calories, Bad Calories. As the author, Gary Taubes, points out, one highly important regulator of fat is an enzyme called lipoprotein lipase (often abbreviated as "LPL"). This enzyme, which is controlled by insulin (among other hormones), essentially attacks and blows up proteins carrying triglycerides. The fats freed by this biochemical explosion get sucked into nearby fat tissue, causing fat to accumulate there.
On the subject of the facts about fat and LPL, Taubes writes that men have higher LPL activity in the abdomen (which would explain why men get beer bellies) and women have higher LPL activity in their thighs and butts (which would explain why women tend to gain weight in those areas). Furthermore, when women go through menopause, their LPL activity increases in the abdomen, which would explain why post-menopausal women gain belly fat.
So the alternative hypothesis tells us that when we eat too many carbohydrates or otherwise mess up our insulin levels, we in turn increase LPL activity in certain areas (e.g. the thighs for pre-menopausal women, the belly for men), and thus this can explain why we fatten in some areas but not others.
Once again, we have a situation in which the Caloric Balance and Lipophilia Hypotheses make two radically different predictions about the facts about fat. Caloric Balance gives us no information whatsoever about how calories become fat. It simply tells us that when we overeat or under exercise, we will "get" fat.
Lipophilia, on the other hand, tells us that enzymatic and hormonal activity (such as what we just discussed about LPL) determines how, when, and where we fatten, and may also give us clues about why certain people are predisposed to fatten in certain areas.