What Determines How Many Calories You Need a Day?

When you're trying to lose or gain weight, or even begin a healthier lifestyle, it is important to know how many calories your body needs to burn per day. Then you can decide how to increase or decrease the number of calories you consume and what exercises you perform.

Basal Metabolic Rate

• Your Basal Metabolic Rate, or BMR, is the amount of calories or energy your body needs to keep the basic function of your body working properly. This includes pumping the heart, breathing and other organ functions.

How to Calculate Your BMR

• BMR is based on your age, gender and weight and can be determined by the following formulas:

  Males
  Age 10-17: 17.5 x (body weight in kg) + 651
  Age 18-29: 15.3 x (body weight in kg) + 679
  Age 30-59: 11.6 x (body weight in kg) + 879
  Age >60: 13.5 x (body weight in kg) + 487

  Females
  Age 10-17: 12.2 x (body weight in kg) + 746
  Age 18-29: 14.7 x (body weight in kg) + 496
  Age 30-59: 8.7 x (body weight in kg) + 829
  Age >60: 10.5 x (body weight in kg) + 596

  For example if you are a 24-year-old male who weighs 79.3kg, your BMR would be approximately 1,892 calories per day. You should note that this is only the amount of calories burned to have your body function; this does not include physical activities such as walking, eating, working out, etc.

Exercise

• A person who is more physically active than another will burn more calories during the day. Added to your BMR should be the amount of calories that you burn while dong physical activities throughout the day.

  There is a simple formula to determine approximately how many calories extra you may burn a day, based on your activities throughout the day.

  If you are very inactive, multiply your BMR by 1.4. You may ask, why are we adding calories if someone is so inactive. Well, even if you are not necessarily exercising you are moving around during the day which does expend calories, even if it doesn't seem as if you are.

  If you live a sedentary lifestyle, multiple your BMR by 1.5.

  If you are moderately active at work, or participate in a moderately active activity throughout the day, add 0.1 to your multiplication for each activity. For example, if you move boxes around at work, and you walk around the block a few times in the evening, you would multiply your BMR by 1.7 (1.5 + 0.1 + 0.1).

  Doing very strenuous activities? Add 0.2 for each activity.

Thermic Effect of Food

• Thermic Effect of Food, or TEF, is defined as an increase in metabolism during the digestion of food, according to the Clinical Nutrition Research Unit at Vanderbilt University. While your body is digesting it is expending more calories, causing your BMR to shift. Of course, some foods are harder to digest than others. Dietary fat is the easiest to digest, while carbohydrates and protein are the hardest.

  If you are adding calories every time you eat food, however, a 100-calorie snack may really increase your calorie intake by only 70 calories, because of the calories used to digest the food.

Illness

• Being sick is another thing that can effect the number of calories you need in a day. To help fight bacteria and viruses in your body, you will burn more energy, or calories, than you would on normal days. This is why so many people lose weight when they are sick: they are expending more calories, and they most likely are not eating enough to cover the extra calories being burned.