Do you wonder, “What should my daily intake of calories be?” Learn how to calculate how many calories you should eat (your daily calorie requirements) to maintain your weight and avoid weight gain or weight loss.
Energy is measured in calories. While not a nutrient, calories are required for sustaining life, for sustaining metabolic processes, physiological functions, muscular activity, growth and development. Main sources of energy (in calories) are carbohydrates, proteins and fats.
What is a calorie?
By definition, a calorie is the amount of energy needed to raise the temperature of one kilogram of water one degree Celsius. The amount of calories you need every day depends upon factors such as gender, age and activity level as well as whether you wish to maintain, gain or lose weight.
How many calories should I eat a day to maintain weight (in general)?
The Estimated Energy Requirement (for Maintenance) or EERM is the daily caloric intake predicted to maintain energy balance, and thus weight, in healthy individuals of a certain age, gender and average height and weight. These averages do not take into account exact body size, level of physical activity, genetics, ethnicity and other possible contributing factors. According to the Institute of Medicine Dietary Reference Intakes (2004), adult males of normal weight, or with a Body Mass Index (BMI) of 22.5, of an average height (5’10”), between the ages of 19 and 50, require approximately 2,500 to 3,000 calories per day for weight maintenance. Women in the same age bracket, of a normal weight, or a BMI of 21.5, of an average height (5’4”), require 1,800 to 2,300 calories daily for weight maintenance. Beyond age 50 for either group the Estimated Energy Requirement will be on the lower end of the spectrum.
Are there specific calculations that take into account my height, weight, gender, age and activity level?
There are two accurate, reliable and expert-recommended mathematical equations for calculating your calorie needs. They are the Harris-Benedict Equation and the Mifflin-St. Jeor formulas and differ for men and women. These equations involve calculating a Basal Metabolic Rate (BMR), or the amount of calories needed daily for basic bodily functions. BMR takes into account height, weight and age. This number should then be multiplied by another number, known as an activity factor, which varies depending upon your level of physical activity. Both equations incorporate the activity factor component.
Men = 66 + (6.3 x weight in lbs) + (12.9 x height in inches) – (6.8 x age in years) = BMR
Women = 655 + (4.35 x weight in lbs) + (4.7 x height in inches) – (6.8 x age in years) = BMR
Mifflin-St. Jeor Equation
Men = 10 x (weight in kg) + (6.25 x height in centimeters) – (5 x age in years) + 5 = BMR
Women = 10 x (weight in kg) + (6.25 x height in centimeters) – (5 x age in years) – 161 = BMR
To calculate your total calorie needs, multiply BMR by the appropriate physical activity factor:
Sedentary = BMR x 1.2
Light activity = BMR x 1.375
Moderately active = BMR x 1.55
Very active = BMR x 1.725
Extremely active/Athletic = BMR x 1.9 or more
For details, see Physical Activity Level (PAL) Guidelines.
Using the Harris-Benedict Equation, the BMR for a 38 year-old woman, 5’4” and 142 lbs = 1,349 calories
Using the Mifflin St-Jeor formula, the BMR for the same woman = 1,310 calories
An activity factor must be added to this number. If you exercise four times per week and are somewhat active throughout the day, you may be ‘moderately active’ (note that activity factors are somewhat subjective). Using the Harris-Benedict Equation, an activity factor of 1.55 equates to 2,091 calories daily for weight maintenance and using the Mifflin-St Jeor formula, total daily calories are 2,030. A compromise between the two calculations is 2,050 calories, noting that two days are rarely the same unless you consume exactly the same foods.
- Food and Nutrition Board: Institute of Medicine. Dietary Reference Intakes for energy, carbohydrates, fiber, fat, fatty acids, cholesterol, protein and amino acids. The National Academy Press, 2002.
- A Report of the Panel on Macronutrients… Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. The National Academies Press, 2005.
- Cornell University. Basal Energy Expenditure: Harris-Benedict Equation.
- MD Mifflin, ST Jeor, et al. A new predictive equation for resting energy expenditure in healthy individuals. J Am Diet Assoc, 2005.