Um, they're wrong.

You should challenge them to a diet of 1000 calories of pure sugar and wheat products vs. 1600 calories of meat and oil.

But seriously, that is just untrue. A calories is NOT just a calorie. There have been NUMEROUS studies to prove this, where people on a low fat, low calorie diet lost less weight than people on a low carb, adequate calorie diet.

Just math, my a$$.