This was particularly interesting:
While it is true for all of us that weight control is overwhelmingly, if not entirely, about calories in versus calories out, it is equally true that the number of calories required for weight loss, weight maintenance and weight gain vary drastically among us. And we even know why, for the most part.
There are, once we are done growing up, three ways we burn calories: physical activity, the generation of heat and just existing. There are technical terms for the second and third: thermogenesis, and resting energy expenditure (sometimes referred to as basal metabolic rate). What should be noteworthy right away is that you are not in charge of two out of the three!
You can choose how much exercise to do. But you don't get to choose how thermogenic you tend to be, and that can matter quite a lot. Like exercise, thermogenesis accounts for roughly 15 percent of total energy expenditure on average, but there is lots of variation on the theme of average. People who generate more heat from calories have fewer available with which to make fat. They tend to be people who can eat a bit more, and stay thin anyway.
But that's a drop in the bucket compared to resting energy expenditure. Roughly 65 percent of calories are burned to support the fundamental workings of cells and organs that keep us alive. The number of calories burned at rest, and the actual percentage of total calories burned this way, also vary substantially around the average. People with a high resting energy expenditure are, in our modern world of epidemic obesity, the fortunate few most people love to hate: the folks who cannot seem to get enough to eat, and can't put weight on when they try.
If you don't control your thermogenic tendencies, nor your resting energy expenditure -- who does? The idiosyncrasies of the genetic hand you were dealt, which are not necessarily idiosyncratic at all.
Take the case of the Pima Indians, for instance.
When the Pimas live a traditional lifestyle and eat traditional Pima foods -- mesquite and tepary beans, for example -- they have unremarkable health. When they live and eat like everyone else in America, they develop almost universal, severe obesity and diabetes. For a time, the Pimas had the highest rates of obesity and diabetes on the planet, and they are still, alas, contenders for those laurels.
The dire plight of the Pimas resulted in intensive study of them, and it led to both revelations, and the obvious. The Pimas have, uniformly, a very low resting energy expenditure. They are, in other words, highly fuel efficient -- even for a fuel efficient species -- and it makes perfect sense. The Pimas lived for generations in a harsh desert climate where food was unusually scarce, and physical activity demands unusually high. Pimas who were not highly fuel efficient simply didn't survive long enough to pass on their disadvantage to any future generation of Pimas. (People who don't live to make babies make very poor ancestors.)
Presumably, the variations in metabolic efficiency to which we are all subject can also be traced to variations in the experiences of our ancestors. But for most of us, the magnitude of genetic mixing that has gone on makes those pathways impossible to follow.
Sigh, if only I had better genes!!