[sn9]

That's more a problem with how difficult and expensive it is to design and implement good studies.

Studies that rely on self-reporting eating history skew the results to ambiguity, but studies in which the experimenters have full and unambiguous knowledge of calories and macronutrients consumed by subjects reveal that the difference in calories digested and the calories burned explains pretty much all changes in weight. It gets only slightly more complicated when talking about body composition (basically, eat enough protein to support your lean body mass and any athletic activity), and even more complicated when talking about long term health (e.g., micronutrient levels that support long-term physiological maintenance mechanisms which are neglected in the sub-clinical nutrient deficient states most people find themselves in).

Fairly simple linear relationships can be used to freely manipulate one's weight, as shown by pretty much any bodybuilder or athlete competing in a sport with weight classes.

Studies aside, it's obvious that relationship between calories digested compared to calories burned is the main determinant of weight as starving populations around the world can tell you. You can't create or maintain mass without the required energy to support cellular metabolism. The physiology and biochemistry is understood well enough for this not to be an issue. The problems professed by the media reporting on studies are mainly ones of measurement (as people don't usually know how to accurately measure their caloric intake, which is why self-reporting studies are basically worthless) and commitment to lifestyles in which they don't chronically overeat relative to their activity level.

[JamesBarney]

It's true if you eat fewer calories you will be thinner, but every study done on diets over the long term(3+ years) shows success rates that hover around 5%(for people who have already succeeded in losing significant weight)

Imagine we gave the startup advice "make lots of money, spend very little money". It is advice that every successful company since the beginning of time has followed. And every failed company has failed to do so. However this advice is exactly as valuable as the advice "eat less calories, burn more".

[sn9]

This is 100% because they fail to adhere to a caloric intake that is at or below their TDEE. That's about behavior, not physiology. They aren't violating the first law of thermodynamics and creating new mass and energy out of nothing. They're eating too much. They aren't tracking their weight and modifying their behavior when they see it going in a direction they and their physicians don't want.

It's no different than the fact that you must spend less than you make to avoid going into debt, and that you must save a certain percentage of your income to save up enough for retirement so that you can continue your standard of living once you retire. And yet we find huge portions of the US population in debt with little to no savings. This doesn't mean the advice is bad or invaluable.

This doesn't mean they're mentally incapable of saving up. That's a behavioral issue, too. And behaviors can be modified. There's research about how to successfully do that, too. Entire industries revolve around modifying behaviors to extract profit from people.

That the studies that you are personally aware of show that people have trouble maintaining a healthy weight suggests, not that it's impossible, but that the subjects don't know how to form and maintain habits.

That people can't implement advice doesn't mean it isn't valuable. At most, it just means they need more advice or counsel. But not different, mutually exclusive, advice.