It is just CICO, whether you won the genetic lottery that makes the calculation simpler or not doesn't mean it's any less of a cop out than saying that it would be simpler for me to be a great basketball player if I were 6 foot 8 instead of 5 foot 5.

Something can be both true and used in a misleading manner.

To use your same metaphor, there are people going around speaking as if height and total hours of training are the only things that matter for basketball skill.

Understand that there are necessary and sufficient conditions. A sufficient condition for obesity is too high chronic caloric intake. A necessary condition is retention of this surplus. Some people will feel correctly full when they overeat high calorie foods, others only if volume is too big, yet others have the distended stomach where even that does not work. Some have hormonal deficit that makes them retain more (e.g. hypothyroidism) or counters satiety signaling. Others have very wasteful metabolism or digestion where less is retained. Some really do highly strenuous activities that just demand more energy.

Ultimately you set a caloric target with a carefully constructed diet and watch the long term weight slope over months. That's the science of it. Even high fat ad lib diets ultimately resulted in caloric input restriction, stronger than other diets they tried. (see Cambridge study)

> Ultimately you set a caloric target with a carefully constructed diet and watch the long term weight slope over months. That's the science of it. Even high fat ad lib diets ultimately resulted in caloric input restriction, stronger than other diets they tried. (see Cambridge study)

Agreed, but I'd characterize all that as focusing on the "Calories In" part. That's complicated enough itself, and avoids implying that the entire situation is some trivial function.

> Calories in is relatively simple.

There are at least two categories of issues that make calories in not so simple: eating disorders and malabsorption disorders.