The fact is if you're fat, you've conditioned yourself to eat too many calories, and eating a normal amount of calories will likely leave you feeling hungrier while you adjust.
http://www.amjmed.com/article/S0002-9343(96)00456-1/abstract
"In the adult US population the prevalence of overweight rose from 25.4% from 1976 to 1980 to 33.3% from 1988 to 1991, a 31% increase. During the same period, average fat intake, adjusted for total calories, dropped from 41.0% to 36.6%, an 11% decrease. Average total daily calorie intake also tended to decrease, from 1,854 kcal to 1,785 kcal (−4%). Men and women had similar trends. Concurrently, there was a dramatic rise in the percentage of the US population consuming low-calorie products, from 19% of the population in 1978 to 76% in 1991. From 1986 to 1991 the prevalence of sedentary lifestyle represented almost 60% of the US population, with no change over time."
On a global scale countries low on the obesity scale (Japan, Singapore, Korea, France) are not teeming with starving under-nourished citizens, and countries high on the obesity scale (Mexico, US) are not lacking gyms, exercise equipment, or opportunities for simple nature walks.