Food is essential to our survival as human beings. The food we consume each day provides us with the fuel, nutrients, and water required for good health and well being. Most things that we eat and drink have calories in them (the basic unit of energy). Some foods have more calories than others. If we want to maintain a healthy weight we need to understand how to effectively balance the energy we consume with the energy we use to rest, work and play each day.
Our bodies require that we take in calories to run effectively. If we sit for most of the day and aren’t physically active then we require less energy. The body isn’t doing much work to survive so it requires less energy. If we are very active and engage in exercise and vigorous activity then we require more energy. The body is using up more energy stores to perform more work and burns through calories much quicker. The “gas tank” needs to be full in order to work effectively during exercise and for a quick recovery.
To effectively determine the amount of calories you need to consume each day there are several factors to consider:
- Body composition (lean body mass, body fat)
- Physical activity and exercise
The Harris-Benedict equation is a formula that can be used to calculate the number of calories required to essentially keep our bodies running when it is at rest (basal metabolic rate or BMR). Your BMR is then used, in conjunction with your activity level, to calculate the amount of calories needed to maintain your current body weight. By understanding the number of calories we need at our current body weight we can then effectively determine a strategy to reach a goal weight in an effective manner (i.e. weight loss or weight gain).
Harris-Benedict Equation for Women
Due to gender differences the calculations for men and women are not the same. Women tend to have less lean body mass and a higher body fat percentage than men.
Step One: Determine your basal metabolic rate (BMR) using the equation below.
BMR = 655 + (4.35 x weight in pounds) + (4.7 x height in inches) – (4.7 x age in years)
Step Two: Apply the Activity Multiplier that best describes your level of activity to calculate your total daily energy expenditure (TDEE) using one of the equations below.
- Sedentary (very little or no exercise): TDEE = BMR x 1.2
- Lightly Active (light exercise or sports 1-3 days/week): TDEE = BMR x 1.375
- Moderately Active (moderate exercise or sports 3-5 days/week): TDEE = BMR x 1.55
- Very Active (hard exercise or sports 6-7 days/week): TDEE = BMR x 1.725
- Extremely Active (very hard exercise or sports 6-7 days/week): TDEE = BMR x 1.9
Once you’ve determined the calories your body requires to maintain your current body weight you can then determine the calories you need to achieve your goal weight. Let’s look an example of a woman who is looking to effectively lose weight.
- Weight: 155 pounds
- Height: 64 inches (5 feet, 4 inches)
- Age: 39 years
- Activity Multiplier: Lightly Active
- BMR = 655 + (4.35 x 155) + (4.7 x 64) – (4.7 x 39)
- BMR = 655 + 674.3 + 300.8 – 183.3
- BMR = 1446.8 kCal
- TDEE = BMR x 1.375
- TDEE = 1446.8 x 1.375
- TDEE = 1989.35 kCal
This person requires 1989.35 calories per day to maintain her weight at 155 pounds. In order to effectively decrease her weight she must decrease her daily caloric intake by an amount that doesn’t upset the body’s comfort level. If you decrease the caloric intake by too much or the body’s metabolism may slow down significantly, causing weight gain rather than weight loss. A decrease of 15 to 20 percent of your daily caloric intake, in addition to increasing activity levels, is an appropriate strategy for positive results.
- Daily Calories for Weight Loss = TDEE – (TDEE x 0.20)
- Daily Calories for Weight Loss = 1989.35 – (1989.35 x 0.20
- Daily Calories for Weight Loss = 1989.35 – 397.87
- Daily Calories for Weight Loss = 1591.48 kCal
With a decrease of 397.87 calories per day, and an increase in physical activity, this woman can expect to lose a pound of fat every nine days. If her goal is to lose 10 pounds she can accomplish that goal, and maintain that goal weight, in less than 3 months.