Why do slim people who eat a lot never seem to put on weight?

A new documentary on SBS - The Truth About Slim People - investigates whether slim people who eat whatever they want but never gain weight just have a fast metabolism or if there are other factors at play.

“An awful lot of people who are overweight have a perfectly normal or even quite a high metabolic rate,” says Prof Brewer says on The Truth About Slim People. Source: iStockphoto/Getty Images