There seem to exist non-negligible differences in individual RMR.

And, though it is my understanding that the '3500 kcals = 1lb of body fat' is a less-than-precise rule of thumb that fails to account for many variables in regard to weight loss, it stills stand to reason that a couple hundred kcals per day would add up to something substantial over the course of, say, even a few years.

So, it seems you could have persons A and B—each eating and exercising at exactly the same level—end up tens of pounds apart from one another in body weight over a relatively short span of years. Over decades, you could see one person end up fit, and the other very obese.

I've noticed two broad opposing views on body weight.

• View 1: Metabolism differences aren't that big a deal. Diet and exercise will make up the differences with relative ease. (Seems to be the tone of the Examine.com article linked above.)

• View 2: Metabolism differences are significant and account for most of the differences in regard to individual body weight.

So, which is it?

It seems to me metabolic differences between individuals are very significant. If person A uses an average of 200 kcal per day less than person B due to differences in RMR, that means person A must expend millions and millions more calories during their lifetime in order to maintain the same body weight. Person A would need to devote an immense amount of combined time towards exercise and/or will power towards eating healthy just in order to "keep up".