I've been debating mentioning this, but I'll throw it out there; maybe it's useful, maybe it's not. There are two big schools of thought regarding managing body composition. One is focused on calories, one is focused on the hormonal response to food (and yes, that is an oversimplification). Just so my biases are clear, I'm pretty firmly in the hormonal camp. I think the "calories in:calories out" idea is an accurate description of thermodynamic fact, but it's almost useless when it comes to explaining
why our bodies do what they do. Here's an example of what, in my understanding, happens when long term weight loss is pursued
purely through caloric restriction:
Bob is overweight, and decides to do something about it. Bob knows that 3,500 calories=1 pound of fat, so he decides to figure out how many calories he's consuming, and cut 500 cal per day in order to lose a pound a week. He's currently eating 3,000 cal/day, so he drops it to 2,500. He enjoys stable weight loss for a while (maybe 1-3 months), but then he stops losing the weight.
----TIME OUT---What's happened is Bob's body is experiencing mild, chronic malnutrition. It has responded by gradually reducing his metabolic output until it matches his food input. His body has ensured that calories in=calories, in order to help him "survive." If he continues consuming 3,000 cal/day, his body will drop his metabolic rate a little bit more, until calories in>calories out, allowing his body to get back to his previous "safe" weight.---TIME IN---
Bob refuses to rebound to his previous weight, so he proactively cuts his calories down to 2,000/day, and his weight loss journey continues. That is, for while, until it starts to slow down again. He drops to 1,800, then 1,600, and finally ends up at a strict 1,400 cal/day diet. He is tired, moody, often cold, mentally dull, and having difficulty sleeping (and sleeping isn't the only bedroom related activity where there's issues).
---TIME OUT---Bob's body has gradually dropped his metabolic rate to match his food intake. In the process, it has down regulated all sorts of systems in order to save energy (and save Bob from the perceived impending starvation), and left Bob with the metabolic capabilities of a child. As he has continued to reduce his caloric intake, his stress levels have gradually risen, resulting in consistently high levels of systemic cortisol, and decreased insulin sensitivity.---TIME IN---
I won't finish Bob's story, but if we were to use statistics as our guide, Bob's stressed out mind would eventually run out of willpower, he would end his diet, and within a year he would be back at his original weight (plus a few pounds, just in case he starts to starve again). This is what happens when calories are the
only consideration in a diet. If we start managing hormones, like insulin, cortisol, and growth hormone, we can actually change the weight that the body
wants to be, along with changing what the body does with the calories it gets. Appetite is reduced, calories are reduced, metabolism is adjusted based on metabolic demands (as opposed to metabolic limitations), and the body can gradually shed weight in a way that is comfortable and sustainable. Not to mention that it still satisfies the gods of thermodynamics, providing weight loss by indirectly ensuring that calories in<calories out.
God bless you if you read that all