The Common Delusion About Corpulence
From 'A Study Of Our Decline' by P Atkinson (January 2003)

People commonly believe that corpulence is nearly always the result of eating too much, that is consuming too many calories, so fat people can reduce their weight by:

This is wrong — it is not the quantity, but the kind, of food eaten, that causes people to become fat. Eating carbohydrates, sometimes even in small quantities, fattens people. And fat is not a carbohydrate but an essential nutrient that not only gives food flavour but also helps to prevent the accumulation of body fat. (See "Eat Fat And Grow Slim")

And it should be noted that vigorous exercise is a health hazard that has little impact upon weight loss.