How Many Calories Do You Really Need?

How Many Calories Do You Really Need?One of the most common questions personal trainers are asked is: “How many calories should I be eating?”  While it seems self-explanatory to some, there is a science behind energy consumption.  Some individuals have different goals, activity levels, and every individual body is different.  This means plugging your height, weight, and activity level into an online calculator to “calculate” your energy needs could be inaccurate due to many variables.  This article is your complete guide to energy consumption, also known as eating calories.  In addition, some of the science involved in energy balance in the body will be discussed.


It is common to forget that a calorie is not something which just simply comes in and out and is control.  A calorie is a form of energy, or heat, which is generally referred to as the amount of energy required to raise one gram of water by one degree C.  While this is generally something you learn chemistry 101, the calorie with which Americans are most concerned is the kilocalorie, which has a different value.  The Calorie in food, which is denoted by a capital C rather than lower case, is similarly defined as the amount of energy required to raise one kilogram of water by one degree C.  Based from that definition, it should be noted that the form of calorie we eat is a kcal.  Once this food is consumed however, what happens inside the body?


Following a meal or snack, the body temperature raises by a varying amount.  Following a very large meal, you may know what it feels like to have the “food sweats”.  This is your body taking in energy and distributing it in the body.  Similar to the “food sweats”, when you exercise at a moderate intensity, you sweat.  Sweating during exercise is not your body’s way of disposing of excess water rather it is a way to cool the body because of the amount of energy being used (the amount of calories being “burned”) is raising the body temperature higher than normal.  Knowing this basic energy information, how does it help in your body weight management?  How many calories should you eat?  How many calories do you use in a typical day with activity?

How Many Calories Should I Eat?

Almost 100 years ago, metabolism equations for predicting energy consumption were developed.  The Harris-Benedict equation for the prediction of energy consumption was developed originally in 1918 and is used in many energy estimation calculators today [1].  What makes this equation the best predictor of metabolic needs is it uses body weight, height, and age.  In addition, it is premised that the basal metabolism (the energy needs for the body to sustain vital processes) is dependent upon age, weight, and height.  While this equation has been around for almost a century, there is one downside: it does not consider daily activity levels.  Fortunately, researchers updated the equation to consider daily activity approximately 30 years ago, making the Harris-Benedict equation the best source for the prediction of caloric needs.  Using the equations below, calculate your metabolism.

Men BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)
Women BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)


Taking in consideration that individuals vary on activity levels and the maintenance of basal metabolism is dependent on how active or not active one is, the Harris-Benedict equation was updated to include a factor to adjust the caloric needs.  Using a very objective look on your physical activity levels, the following section should give you your factor for your basal metabolism given your specific activity level [2].  Multiply your energy needs from the Harris-Benedict equation above by the factor adjustment below to get your daily requirements.

No Exercise Metabolism x 1.2
Light Exercise (1-3 days/week) Metabolism x 1.375
Moderate Exercise (3-5 days/week) Metabolism x 1.55
Heavy Exercise (6-7 days/week) Metabolism x 1.725
Athletes and Extreme Exercise Metabolism x 1.9


Now that you can do the equations by hand and you have a better understanding of energy balance, consider looking online for Harris-Benedict equations.  If you are interested in a more accurate measurement rather than a prediction, consider discussing a metabolic test with a trainer at your gym.  Metabolic tests often include breathing for about 20 minutes in a tube at a resting state to determine your caloric needs.  These tests vary in price and are very accurate.  If weight loss is in your near future, it is highly recommended to receive a metabolic test to determine your metabolism to better support your weight loss journey.




About the Author

, Celebrity Personal Trainer and Fitness & Nutrition Expert headquartered in Scottsdale, AZ. He specializes in helping men and women achieve weight loss, muscle building, toning and other customized fitness & nutrition programs to create a Healthy Lifestyle. James offers private luxury personal training, 12-week custom workout plans, and personalized nutrition meal plans. Follow on Google+.

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