Fat is always on our minds. We waste many productive hours thinking about the fat that’s on our plate, our bodies, other people’s bodies, and (for purely scientific reasons) the bodies of scantily clad celebrities on the Internet. Other body parts don’t come close to getting this much attention, which is probably why fat is the subject of a messy collection of mistakes, myths, and misinformation. Here are some fat factoids you might have encountered:
• Muscle turns to fat. Muscle and fat are different types of tissue, and the body can’t convert one to the other any more than you can transform a pear into a chocolate truffle. However, your fat sits on top of your muscles, which means that a small weight gain can quickly mask those six-pack abs.
• A calorie is a calorie. There are a dizzying range of factors that can influence how well your body transforms food into energy and (ultimately) fat, from the quality of the bacteria in your digestive tract to the combination of nutrients in the food you eat. So-called experts that miss this subtlety warn that a single extra glass of juice a day can add up to dozens of pounds of weight gain over a year, which is clearly nonsense. Other than paranoid dieters, no one eats with such maniacal precision. The truth is that the body is miraculously successful at preserving its preferred weight.
• Thin people have faster metabolisms. This is partly true, in the sense that naturally thin people often expend more energy in small, natural ways (for example, with constant fidgeting). However, people of all body types appear to burn calories in roughly the same proportion to their weight, which means that obese people actually need faster metabolisms to maintain their extra poundage. However, there’s one huge exception: If you start an extreme diet, your metabolism will fight you, slowing itself down to a calorie-conserving crawl. Similarly, pig out in an effort to put on pounds, and your metabolism will speed up to keep you at your current weight.
Source of Information : Oreilly - Your Body Missing Manual (08-2009)