You already: Cook for your family (76 calories for 20 minutes).
You should also: Bake goodies for them, or for your neighbors or coworkers. Ever wonder how the pastry chefs you see on TV stay so slim? It may have to do with the fact that they burn about 95 calories during 30 minutes of baking (it also helps that it's really hard to bake while sitting down). The trick, of course, is resisting the urge to lick the buttercream from the spoon, or to sample the cookies when they come out of the oven.
Bonus tip: The recipe for this rustic tart, which is bursting with antioxidant-rich fruit, involves lots of energetic mixing and rolling. If you pick the berries yourself, you'll burn an extra 76 calories (for 20 minutes).