How Many Calories Do I Require Each Day?
Question: “How can I determine how many calories are required daily to maintain my present weight?”
Calories are units of energy obtained from the proteins, fats and carbohydrates that we eat and drink. Maintenance calorie requirements can vary widely from one individual to the next due to a variety of factors that include age, gender, body weight, amount of muscle mass and activity levels. A person’s total energy expenditure (TEE), the total number of calories the body requires daily, is determined by three primary components.
1. Energy required to fuel basal (resting) metabolic rate (BMR)
BMR represents the energy needed to maintain the body when at rest. These calories are used to support vital body functions such as breathing, pumping blood, growing hair, and making new blood cells. For most people, BMR accounts for 60 to 75 percent of calories burned each day.
Your BMR is in large part determined by genetic factors, although you can increase it to some extent. One way to do so is to add muscle to your frame through strength training. Muscle is a metabolically active tissue that requires energy (calories) simply to maintain it, so when you add muscle mass, you automatically increase basal metabolism. In general, the larger and more muscular you are, the higher your BMR. An increased BMR enables you to burn extra calories 60 minutes an hour, 24 hours a day, just by being alive.
2. Energy required for digestion and absorption of food
Our body also uses energy to digest and absorb the food that we eat. This is commonly referred to as the thermic effect of digestion and accounts for approximately 10 to 15 percent of our TEE each day. Increase the number of calories burned due to the thermic effect of digestion, at least to a limited extent, by consuming smaller but more frequent meals or by increasing the protein content of meals.
3. Energy required to fuel physical activity and exercise
This calorie-burning component accounts for the energy required daily for physical activity and is the most variable of the three major components. It can be as low as 10 percent of daily calorie expenditure for sedentary individuals or as high as 80 percent for competitive athletes who train for several hours each day. In short, the more physically active you are, the more calories you will burn.
Estimating calorie needs
There are several ways to obtain a reasonable estimate of how many calories are required daily to meet energy needs. If body weight has remained stable for the past few weeks, you can safely assume that you are consuming roughly as many calories daily as you are expending.
To get a more specific idea of how many calories that entails, record the approximate calorie content of everything you eat and drink for the next week, then divide the total by seven. The resulting number should approximate the daily calorie intake required to maintain your present weight.
However, if you are one of those people who do not enjoy keeping a calorie log of everything you consume, there are predictive formulas that can estimate daily energy requirements. The following method, adapted from the American College of Sports Medicine (ACSM) manual “Complete Guide to Fitness & Health,” is based on two factors: present body weight and estimated level of physical activity.
Each of four possible activity levels (sedentary, moderately active, very active and competitive athlete) is linked with a “calories required for each pound of body weight” for that level of physical activity. ACSM estimates that a sedentary person (office job, little exercise, most Americans) requires 14 calories per pound of body weight per day. A moderately active person (weekend exerciser) requires 15 calories per pound. A very active person (3 or more sessions of vigorous physical activity per week) burns 16 calories per pound. A competitive athlete (vigorous daily training) requires 17 or more calories per pound.
Since this method requires you to “guesstimate” activity level, there is an inherent margin of error associated with the calculations. I suggest being cautiously conservative when selecting your activity level, as I feel most people overestimate how physically active they actually are.
To obtain an estimate of your daily calorie requirement, simply multiply your body weight (in pounds) by the number of calories required per pound associated with your activity level. Using myself as an example: I weigh about 170 pounds and consider myself a very active person. To determine my calorie needs, I multiply 170 pounds by 16 calories per pound to obtain a TEE of approximately 2700 calories per day. Based on past experiences, I am confident that is a reasonably accurate estimate of my daily caloric requirement.
Using the ACSM formula to calculate energy needs can provide a general idea, a starting point, for managing calorie intake. Keep in mind that the calculation is an estimate only; it is not an exact science! I would suggest that over the span of a few weeks, limit daily intake of calories to the calculated estimate, and at the end of that period, note any changes in body weight. If your weight has remained relatively stable, then you can assume the TEE estimate was fairly accurate. If not, adjust calorie intake accordingly depending upon whether you gained or lost weight.