The digestion and absorption of food takes about 10 percent, and the energy you use during physical activity and recovery takes approximately 15-30 percent.

To estimate how much daily energy you spend, multiply your weight in pounds by the amount of given below for one of three lifestyles. For example, for a sedentary 140 pound woman: 140 x 12.5 = 1,750 calories per day.

• Sedentary lifestyle: You don’t move around much, and tend to take an elevator instead of the stairs. Men multiply by 14-15; woman 12-13.
• Moderately active: You exercise for one hour 2-3 times per week, or walk about 2 miles each day. Men, multiply by 16-17; women 14-15.
• Very active: You run, swim, or do high-energy exercise every day. Men, multiply by 18; women 16.

Source:  American Institute for Cancer Research Newsletter. Winter 2007.