We all have one. The skinny friend who never says "no" to dessert. Why can they have a huge slice of cake when we gain weight just looking at it? Well, it turns out that some people are naturally fat-proof. Here are the details: During a study done for the BBC's Horizon documentary series, researchers had volunteers DOUBLE their usual food intake. For most of the participants, that meant eating anywhere from two to three thousand calories a meal! They also had to stop exercising. After a month, the researchers got a good look at the different ways our bodies handle excess calories: Most people did what you'd expect - gained a lot of weight. On average, their body fat increased by more than 10%. However, when the experiment ended, they quickly returned to their original weight without making any special effort. Then there was the 'skinny friend' group. They ate all their calories like the other group, but their weight didn't change.* One of the volunteers gained almost 15 pounds, but his percentage of body fat went down! He's one of the few who has a metabolism that turns extra calories into muscle instead of fat. What's this mean to you? Well, some people are born lucky. Then there are the rest of us. Dr. Rudy Leibel, a professor of medicine at Columbia University, believes we all have an "adult weight" that's programmed at birth. When our weight varies from that set point, our bodies compensate to get us back to it. Now, if you want to drop a few pounds, this doesn't mean it's hopeless. While the set point makes it almost impossible for naturally skinny people to gain weight, Dr. Leibel says it's only responsible for about 50% of the trouble people have losing it. So, the rest is up to you. Making better food choices and getting more exercise will make a difference, and if you do that consistently, you can re-program your body. When you hang out with your 'eat anything' friends, do it someplace besides a restaurant.