Before you get started in any diet and fitness plan you will want to know what your daily caloric requirements are. A few simple mathematic calculations will give you the information you need to get started. Many skip this step because they don’t feel like figuring it out. It’s really simple and only takes 2 minutes.
-First calculate your resting metabolic rate (RMR)
Body weight x 10 = RMR (in calories)
165lbs x 10 = 1650 calories
According to the calculation, I need 1650 calories to do basic life functions (breath, grow hair, pump blood…) and maintain weight.
-Next calculate daily activity burn
RMR x 20% = Daily activity burn
1650 x 20% = 330 calories
Daily burn accounts for calories required for daily movement aside from exercise (work, shopping, going to the mailbox, everyday tasks…). This is a ball park figure, everyone will be different (Obviously a package delivery man will burn more calories than a computer programmer).
-Now add your RMR and Daily activity burn and the extra calories required for exercise (P90x is about 600)
1650 + 330 + 600 = 2580
According to the calculation I need about 2580 calories in order to maintain my body weight while doing P90X.
This amount, is the energy amount that would be used to select your nutrition level in the P90X Nutrition Guide. I fall into Level II.
If you are performing other exercises, such as running, you will want to account for that as well by adding more calories (about 600 for every 45-60mins of high intensity exercise)
If you want to lose weight, you need to burn more calories than you consume.
If you want to gain weight, you need to consume more than you burn.
Exercise + Nutrition + Support = Success