(the less you weigh, the less your metabolism rate, basic physics)
Assuming a similar level of physical activity, if you have two guys, one who weighs 180 pounds with only 10% body fat and another guy who weighs 200 pounds with 40% body fat, I'm fairly confident that the leaner, more muscular guy who weighs less will have the higher metabolic rate.Just reviewed my lectures on this subject...and i was right first time, the less you weigh, the less your metabolic rate. A decrease in total mass (does not matter whether fat or fat free mass) leads to your basal metabolic rate decreasing. Also the amount of energy expended doing exercise also decreases. All basic physics.