A friend forwarded me an post about whether or not a person should eat more on the days that they exercise. It said that most of us don't exercise enough to justify extra calories. But, here is the general guideline: Multiply your weight by 13. The total is how many calories you should eat daily, whether you are not exercising at all or if you are working out moderately for an hour or less. On days that you exercise more than an hour, add 100 to 200 calories per additional hour. So, if you took a two hour hike, add 150 calories to a snack or meal that day. If your energy level is flagging during a particularly active week, try adding more protein to breakfast (a scoop of cottage cheese or an egg) and snacks (a handful of almonds, string cheese).