When we talk about how many calories equal a pound, we’re essentially dealing with two concepts. The first is how many net calories, in terms of caloric intake vs. caloric expenditure, it takes to add a pound of weight and, conversely, how many net calories it takes to lose a pound (2) of weight. In either case, the answer is the same. One pound is equal to approximately 3500 calories (3). That means that in order to lose a pound of weight per week, your body needs to expend an additional 3500 calories each week. Similarly, gaining a pound of weight requires adding 3500 net calories. So, when we talk about adding or putting on weight and losing weight, just what are we adding to and subtracting from?
Your Basal Metabolic Rate (BMR) is the amount of energy your body expends when it is completely at rest. That is to say, if you were to do absolutely nothing all day, your body still needs a specific amount of energy (5) to maintain its vital functioning. That energy amount is called the BMR (4). Your BMR is based upon your age, gender, weight and height. So, the BMR for a 30-year-old, 5’10” man who weighs 180 pounds is higher (at 1784 calories) than the BMR for a 30-year-old 5’4” woman who weighs 140 pounds (1341 calories). In these examples, the hypothetical male would need to consume 1784 calories to maintain his daily functioning and his current weight and the hypothetical female would need to consume 1341 calories to maintain her daily functioning and present weight. Of course, few of us live completely sedentary lives. Physical activity increases your BMR and the more physically active you are the higher your caloric needs. When adding physical activity to the equation, BMR needs to be recalculated in order to find out your total energy needs. To use one of the examples above, the 5’10” male, his BMR calculated using the Harris-Benedict or Mifflin-St. Jeor equation (6), which is considered to be the most reliable, is:
Male: BMR = 10 x weight (in kilograms) + 6.25 x height (in centimeters) -5 x age + 5
(For your reference the Female BMR equation is as follows: 10 x weight (in kilograms) + 6.25 x height (in centimeters) -5 x age – 161)
So, 10 x 81.8 + 6.25 x 177.8 – 5 x 30 + 5 = 818 + 1111.25 – 150 + 5 = 1784 calories. But, if you consider physical activity, that BMR changes. To account for physical activity, your basic BMR equation must be multiplied by another factor based on your activity level. The following are the basic activity factors used to calculate BMR based on activity level:
- 1.200 = sedentary (little or no exercise)
- 1.375 = lightly active (light exercise/sports 1-3 days/week, approx. 590 Cal/day)
- 1.550 = moderately active (moderate exercise/sports 3-5 days/week, approx. 870 Cal/day)
- 1.725 = very active (hard exercise/sports 6-7 days a week, approx. 1150 Cal/day)
- 1.900 = extra active (very hard exercise/sports and physical job, approx. 1580 Cal/day)
So, again, using the example above, if the hypothetical male is moderately active his BMR of 1784 needs to be multiplied by 1.55. That would make his daily caloric needs 2765 – almost 1000 calories greater than his BMR. If he wanted to figure out how many calories equal a pound of weight loss each week, he would need to reduce his caloric intake by 500 calories per day (500 calories x 7 days = 3500 calories, which equals a pound of weight). Adding 500 calories each day or, and this is important, reducing his energy expenditure (physical activity level) by 500 calories each day would lead to a weight gain of one pound per week. Whether we are looking to lose weight or simply maintain a healthy weight, it is important to be aware of the fact that not only do changes in diet impact your caloric needs but so do changes in activity levels.