That's a load of bullshit and one of the sorry excuses that fat people have invented to absolve themselves of the responsibility for their own predicament.
Fat is nothing more than stored energy and if you understand the laws of thermodynamics, you'll know that energy cannot be produced from nothing. It can only be converted from one form to another.
Anyone who consumes more energy than they burn will end up putting on weight while those who burn more than they consume will lose weight. Show me someone who can defy this equation and you'll have a solution to all the world's energy problems.
When it comes to finding the right balance between input and output, metabolic rate variations from one person to another come into play. Those with high metabolic rates can enjoy the luxury of eating lots without getting fat. Those with extremely slow rates put on weight very easily.
However, ones metabolic rate isn't fixed. It can be raised by leading an active lifestyle while sedentary habits slow it down. Crash course diets also cause a drastic lowering of the metabolic rate because the body responds to starvation by burning less calories in preparation for what the body perceives to be an impending famine. That's why dieting alone never works long term.
When I was in school, there was an average of only one fatty per cohort and he was usually the son of a millionaire who didn't have to lift a finger to do anything. The rest of us were thin because we walked or cycled to school, played hantam bola during recess and soccer after classes.
For more info read
http://www.nhlbi.nih.gov/health/health-topics/topics/obe/causes.html