8 things you always wanted to know about dieting (but never knew who to ask)
Does caffeine kick-start your metabolism? Will grapefruit help you burn fat? We debunk the myths and provide the skinny on your most pressing weight-loss questions:

Q: Can coffee really rev up my metabolism?
A: It’s true: Java can stoke your calorie-burning furnace — provided you drink it black. A study in the journal Metabolism found that the caffeine in two cups of coffee may cause a 145-pound woman to expend up to 50 extra calories over the next four hours. But stirring in milk, cream, or sugar can cause your insulin levels to rise, which diminishes that metabolic effect.

Also, as caffeine is a diuretic, it can cause you to lose water. A cup of coffee a day can cause your body to lose as much as four cups of water. In the long run, you may end up becoming dehydrated and dependent on coffee for an energy boost.

Text: Liz Plosser & Long Li Yann

Read this article in the August issue of Shape. Out now at newsstands.