Figuring your energy needs

Sometimes you can eat your cake and have it, too

Food is fuel. When your body breaks it down, it creates the energy that your body uses to walk to the fridge for a snack, run a marathon, or hold this book in your hands.

Calories are what nutritionists use to measure how much energy is stored in that food in your fridge. To be exact, 1 calorie equals the amount of energy it would take to raise the temperature of 1 kilogram (2.2 pounds) of water 1 degree Celsius (1.8 degrees Fahrenheit). Fats yield 9 calories per gram, for instance, and carbohydrates provide about 4.

Why, you may wonder, are we told to stay away from fatty food? Couldn't we all use a little more pep? Unfortunately, it doesn't quite work that way. If you are a moderately active person, you probably require about 15 calories for every pound you weigh to give you all the energy you need to get through your daily routine. Your body, marvel of efficiency that it is, will store any caloric intake above that amount for a rainy day.

The problem is, your body stores those calories in the form of fat - a lumpy but efficient sort of battery system. To make matters worse, a major new study has shown that when you do lose weight, your metabolism adjusts by burning calories more slowly, making it even harder not to regain that lost weight.

The bottom line: If you store an extra 3,500 calories of energy somewhere, that somewhere is going to gain about a pound of body fat.

Who Needs What Calories?

The energy you expend regulates how much energy you should take in. Light activity like housecleaning, carpentry, restaurant work, or golfing requires fewer calories than moderate activity like weeding, tennis, and dancing, or heavy activity like manual digging and football.

Category Age Calories Per Day
Light Activity Moderate Activity Heavy Activity
Children 4-6 . 1,800 .
. 7-10 . 2,000 .
Males 11-14 . 2,500 .
.15-18 . 3,000 .
. 19-24 2,700 3,000 3,600
. 25-50 3,000 3,200 4,000
. 51+ . 2,300 (2) .
Females (1) 11-18 . 2,200 .
. 19-24 2,000 2,100 2,600
. 25-50 2,200 2,300 2,800
.51+ . 1,900 (2) .

1. Pregnant women in second or third trimesters should add 300 calories; nursing mothers, 500.
2. Based on light to moderate activity.
Source: National Academy of Sciences.


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