Read this amazing book!

I'd say it boils down to one main thing: HORMONES. All of them play a part, the most important one usually being insulin, but of course also the thyroid and estrogen and others.

Food = the way different food and amounts affect hormones, particularly insulin.
Exercise = the way it affects hormones.

There is even a rare disorder that exemplifies this -- a person can be starving and emaciated on parts of their bodies, let's say the upper body, and be very obese on another part, for example the buttocks and upper legs. How? Why? Hormones.

I recommend you read a book that rocked my viewpoint, and I've been a health fanatic 15+ years now: "Good Calories, Bad Calories". I think the author's name is Gary Taubes, but you can find the book with just the title. I HIGHLY recommend reading it. The author started out looking at existing research, and was himself very surprised with the conclusions the results indicate. It goes into so much detail, and the last 100 pages are just lists of the many, many studies referenced!

Hormones control what happens in regards to the body's fat stores, and trying to fight that with simply calorie control and/or exercise can be effective (partially because of the way they affect hormones) but sometimes that only works to a degree and can be a losing battle. Move past the old "calories in, calories out" ideology that isn't entirely accurate. More important is purposely addressing the hormone levels and their effect on metabolism.

The answer is still found in the types and amounts of foods eaten, exercise, and perhaps supplements, but as seen through a different perspective.

EDIT: The author's name is Gary Taubes, not Weintraub as I previously stated. Tweet