Set points, settling points and some alternative models: theoretical options to understand how genes and environments combine to regulate body adiposity

Set points, settling points and some alternative models: theoretical options to understand how genes and environments combine to regulate body adiposity.

This is a paper I’ve linked before, and for good reason. It’s refreshing to see what the fields of nutrition and obesity research are actually doing, as contrasted with the caricatures and kooky pseudoscience passed around the internet (i.e. “starvation mode”). It’s also a neat illustration of how biology and environment interact to regulate body weight, which is a factor often left out of the deterministic causal-chains-of-biomolecules thought process.

In a larger scope, it also illustrates why we should be very careful of saying that any given thing “causes” or “explains” any particular outcome in a tightly-knit network such as regulation of body weight. Neat and tidy stories about molecules appeal to human brains but don’t always reflect the reality in any meaningful way.

A Calorie Isn’t a Calorie(?)

Ever since Nicholas Clement defined the calorie as a unit of heat back in the 19th century, we’ve used it as a measure for the energy available to our bodies in the food we eat. The so-called “kilogram calorie” (or kilocalorie), which you see on nutritional labels, equates to the energy needed to raise the temperature of one kilogram of water by one degree Celsius.

These capital-C Calories serve as an approximation for the amount of energy we take in from our food, as well as the amount of energy we expend over the course of our day, through a combination of essential life-processes and any additional physical or mental activity we add on top of the baseline.

Later on in the 19th century, chemist Wilbur Atwater used oxidation reactions to test the energy content of various nutrients, inclusive of corrections for rates of digestion and the production of urea. Atwater’s values, roughly 4 calories per gram for protein and carbs and 9 kcals/gram for fats, remain in use today.

Lately, however, there’s been a trend towards rejecting this model. Not only are calories thought to be insufficient — or outright irrelevant — in explaining the continuing rise in obesity, but the deeper reason is that “a calorie isn’t a calorie”.
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