Discovering how many calories your body uses in a day otherwise known as your “Daily Energy Expenditure” unlocks the mystery behind weight loss. Imagine finally being able to pinpoint how many calories you should eat in a day to maintain your weight, or to safely and effectively lose weight. Calculating your Daily Energy Expenditure is just about as easy as balancing your checkbook – or for some – maybe even easier once you know the math inside your body!
To determine how many calories approximately you should eat in a day to either maintain, lose or gain weight you need to first calculate your Basal Metabolic Rate (BMR) using the Harris Benedict Equation for BMR:
For Men: (13.75 x weight in kg) + (5 x height in cm) – (6.76 x age) + 66 = BMR
For Women: (9.56 x weight in kg) + (1.85 x height in cm) – (4.68 x age) + 655 = BMR
For a 46 year old woman that weighs 155 pounds and is “lightly active” she will have an estimated BMR according to the Harris Benedict Calculation of – 1,431 Calories.
BMR = 1,431 Calories in a 24 hour day
9.56 x 70.30 = 672.06 + (319.53 – 215.28) + 655 = BMR
672.06 + 104.25 + 655 = 1,431 BMR
Now that you have calculated the “Basal Metabolic Rate” you now need to add in an approximation of how many calories this woman will use in a day doing all of her daily activity. To most accurately determine how many calories used in a 24 hour day, you will combine the “Basal” or “Resting” energy expenditure (the amount of calories used while sleeping at night and that are used while at rest (sitting, and/or lying down) throughout the day. This total number of calories called the BMR will then be added to the calories estimated that are used in daily activities while moving around, not staying in a seated or supine position throughout a 24 hour day. The combination of the BMR along with the estimated total number of calories that are used in a day in movement activities results in a number called the Daily Energy Expenditure (DEE). The DEE simply is an estimation of how many calories you use in a full 24 hour day – at the estimated activity level you selected when completing the calculation, that also includes calories used while at a “basal” or “resting” state.
How To Calculate Your Daily Energy Expenditure (DEE)
The Harris Benedict Equation is a formula that uses BMR and then applies an activity factor to determine the total daily energy expenditure (calories). The only factor omitted by the Harris Benedict Equation is lean body mass. Remember, leaner bodies need more calories than less leaner ones. Therefore, this equation will be very accurate in all but the very muscular (will under-estimate calorie needs) and the very fat (will over-estimate calorie needs).
To determine total daily calorie needs, multiply the BMR from the equation listed above by the appropriate activity factor listed below:
- For a sedentary lifestyle (little or no exercise) : Calorie-Calculation = BMR x 1.2
- For a lightly active lifestyle (light exercise/sports 1-3 days/week) : Calorie-Calculation = BMR x 1.375
- For a moderately active lifestyle (moderate exercise/sports 3-5 days/week) : Calorie-Calculation = BMR x 1.55
- For a very active lifestyle (hard exercise/sports 6-7 days a week) : Calorie-Calculation = BMR x 1.725
- For an extra active lifestyle (very hard exercise/sports & physical job or 2x training) : Calorie-Calculation = BMR x 1.9
Calculated DEE for the 46 year old, slightly active woman in the example above:
DEE = BMR x 1.375 (lightly active daily lifestyle)= 1431(BMR) x 1.375 (Activity Factor) = 1967 Estimated Total Calories Needed For A 24 Hour Day to maintain the current weight of 155 pounds. If this women would like to lose 1 pound of her body weight, she would have to create a calorie deficit to utilize or “burn”1 pound of weight on her body.
Applying Your DEE Knowledge To Lose Body Fat!
There are approximately 3500 calories in a pound of stored body fat. So, if you create a 3500-calorie deficit through diet, exercise or a combination of both, you will lose one pound of body weight. (On average 75% of this is fat, 25% lean tissue) If you create a 7000 calorie deficit you will lose two pounds and so on. The calorie deficit can be achieved either by calorie-restriction alone, or by a combination of fewer calories in (diet) and more calories out (exercise). This combination of diet and exercise is best for lasting weight loss. Indeed, sustained weight loss is difficult or impossible without increased regular exercise.
If you want to lose fat, a useful guideline for lowering your calorie intake is to reduce your calories by at least 500, but not more than 1000 below your maintenance level. For people with only a small amount of weight to lose, 1000 calories will be too much of a deficit. As a guide to minimum calorie intake, the American College of Sports Medicine (ACSM) recommends that calorie levels never drop below 1200 calories per day for women or 1800 calories per day for men. Even these calorie levels are quite low. An alternative way of calculating a safe minimum calorie-intake level is by reference to your body weight or current body weight. Reducing calories by 15-20% below your daily calorie maintenance needs is a useful start. You may increase this depending on your weight loss goals.