Look, "he/she has a slow metabolism" or " I have a fast metabolism" is usually in reference to how hard it is for someone to lose weight or gain or about how much food they can consume. But first you guys need to even define what "metabolism" is but SIMPLY put, your metabolic rate is the total energy expenditure of the body. Everything that the body does...breathing, heart beat, organ function, etc all require some amount of energy. The rate differs from person to person, you and someone else can have the same activity level, diet and weight but still gain or lose at different rates based on differences in metabolism.
Combining food with oxygen releases the energy needed to function. Every activity that happens requires some form of energy. The total of all of these actions is measured in calories (unit of heat). This is your metabolic rate (metabolism), the rate on which your body consumes energy.
60-70% is the largest and falls in your RMR (resting metabolic rate). Long story short (and I can go on ALL DAY). Three things have to come into play.....Resting metabolic rate (RMR - the sum of BMR + basic living), diet induced thermo (DIT) and energy of activity.
60-70% RMR
20-30% Activity induced
10% dietary
Quick example of TEF.....Fat has a low TEF of about 3-5% while protein is A LOT higher at about 30-35% (for those that understand TEF)
BTW, Disgusted has it right with the lower carbs.