The calories-in calories-out model is attractive, but it doesn't appear to be all that accurate, or at least it's incomplete. The body responds differently to different foods. They might have different effects on various hormones (e.g. the ones that regulate hunger), and they might be broken down and redistributed in different ways. In one study (Kekwick and Pawan), three groups of people were put on 1,000 calorie diets of 90% fat resp. 90% protein resp. 90% carbs. The first group lost 0.9 lbs / day, the second group lost 0.6 lbs / day, and the third group gained 0.24 lbs / day. (I don't know to what extent the study controlled for exercise but I think it's safe to assume that the difference in the amount of exercise that each group did wasn't large enough to explain these results.) As Tim Ferriss puts it in The 4-Hour Body:
The creator of the "calorie" as we know it, 19th-century chemist Wilbur Olin Atwater, did not have the technology that we have today. He incinerated foods. Incineration does not equal human digestion; eating a fireplace log will not store the same number of calories as burning one will produce. Tummies have trouble with bark, as they do with many things.
In the context of solving the specific problem of fat loss, one goal is not to lose muscle, and what you're eating should affect how easy it is to target fat and retain muscle as well.
And, of course, diets don't work if they can't be maintained. The fact that different foods affect the hormones that regulate hunger differently (some foods even make you hungrier!) means that different diets, even with the same number of calories, require different amounts of willpower to maintain.
1,000 calorie diets ... third group gained 0.24 lbs / day
I noticed I was confused. This doesn't seem consistent with the results of the Minnesota Starvation/Semistarvation Study. I went to Wikipedia.
...Kekwick and Pawan, 1956 conducted a study of subjects consuming 1000-calorie diets, some 90% protein, some 90% fat, and some 90% carbohydrates. Those on the high fat diet lost the most, the high protein dieters lost somewhat less, and the high carbohydrate dieters actually gained weight on average. Kekwick and Pawan noted irregularities in their study (pat
Follow-up to: Boring Advice Repository
Many practical problems in instrumental rationality appear to be wide open. Two I've been annoyed by recently are "what should I eat?" and "how should I exercise?" However, some appear to be more or less solved. For example, various mnemonic techniques like memory palaces, along with spaced repetition, seem to more or less solve the problem of memorization.
I would like people to use this thread to post other examples of solved problems in instrumental rationality. I'm pretty sure you all collectively know good examples; there's a comment I can't find from a user who said something like "taking a flattering photograph of yourself is a solved problem," and it's likely that there are other useful examples like this that aren't common knowledge. Err on the side of posting solutions which may not be universal but are still likely to be helpful to many people.
(This thread is allowed to not be boring! Go wild!)