I can't speak for anyone else but in my case, an excess of calories usually results in me being an awful lot hotter as my body burns off the extra energy. I'm not a biologist but I was under the impression that a release of insulin was required to store excess energy as fat? That would suggest it's more related to blood sugar spikes than actual energy consumed.
There are absolutely different ways bodies can handle excess calories, and it's pretty clearly documented.
For some people, their body will try to burn the extra calories - this in part may be due to the amount of brown fat, which is one of the mechanisms the body uses to generate heat. For others, their body will store as much energy as possible as fat, and they need to increase their activity level to compensate.
In addition, your body can become more efficient, using less energy based on the calories you consume. This is one reason that it can be very hard to keep weight off after you lose it.
Metabolism is an incredibly complex process, and while we understand a lot of the pieces, we do not yet have a full understanding of how those pieces fit together, and how to use that information to help people change their metabolism beyond more than very general advice (build muscle, be more active), and some things were sort of taken for granted - such as how it used to be thought that lactic acid was responsible for muscle soreness in the days after workouts, when more recent research has shown this isn't the case: http://www.nytimes.com/2006/05/16/health/nutrition/16run.htm....
Maybe in another 50 years we'll have people who can really understand this stuff.
