Calories and Losing Weight

As a general rule, if you consume less calories that your body needs, you will lose weight. Your body will take what it needs from its stored fat and convert it to energy. In practice, it’s not that simple.

A Calorie (food calorie or kcal) is defined as the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. To determine the number of calories that are in a food item, you can burn the food in a closed container surrounded by water, and see how many degrees that water temperature rises. Or, more simply, you can look at the nutritional label on your processed food. For  information about how calories are calculated today, see this Scientific American article.

In this article in the Getting Healthy Series, you will complete the following tasks:

Every person burns calories at a different rate based on sex, height, weight, and age. Other factors can also affect your daily calorie burn, including the amount of activity in which you engage on a daily basis, and any health issues that affect your metabolism (especially thyroid issues). Before you can determine how many calories that you need to consume in order to lose weight, you need to know your Basil Metabolic Rate (BMR). The BMR is the rate at which you burn calories if you did absolutely nothing in a day.

Calculating Your BMR

There are two ways to calculate your BMR. You can estimate it using a formula, or you can visit a registered dietitian or your local fitness center obtain a measurement. To measure your BMR with accuracy, the dietitian or fitness center will have you sit quietly in a chair, doing nothing but breathing for an hour or so, while they measure the amount of oxygen that you breathe in and the amount of carbon dioxide that you expel. This can be expensive and time-consuming, and is not necessary for most people. You should test the proven Mifflin St. Jeor equation before taking further action.

To calculate (estimate) your BMR, collect the following information:

  • Your weight in pounds or kilograms
  • Your height in inches or centimeters
  • Your age in years

Use one of the following equations, based on whether you are taking your measurements in metric or imperial units:

Mifflin St. Jeor Equation (Metric)
BMR (men) = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) + 5
BMR (women) = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161

“A new predictive equation for resting energy expenditure in healthy individuals.” US National Library of Medicine National Institutes of Health. Accessed January 1, 2016.

Mifflin St. Jeor Equation (Imperial)
BMR (men) = (4.55 x weight in pounds) + (15.88 x height in inches) – (5 x age in years) + 5
BMR (women) = (4.55 x weight in pounds) + (15.88 x height in inches) – (5 x age in years) – 161

Calculated using 1kg = 2.2 lb, and 1 inch = 2.54 cm

For example, if you are a 35 year old 5’9″ woman that weighs 200 lb, your BMR is 1670:

BMR = (4.55 x 200) + (15.88 x 69) – (5 x 35) – 161 = 1670

Factoring Your Activity Level

Your BMR is the number of calories that you burn when sitting still and breathing. Realistically, you do more than that in a day. To determine the number of calories that you burn on an average day, multiply your calculate BMR by the appropriate factor for your lifestyle in the table below:

If you Your Activity Level is
Use the Activity Factor
Have a desk job or sit for most of the day Sedentary BMR x 1.1
Are on your feet and walking around for at least half the day
(Stay-at-home parents, salespeople, and doctors fall into this category.)
Light activity BMR x 1.2
Are on the move pretty much all day, with a few limited periods of being sedentary
(People in this category include gardeners, carpenters, and mail carriers.)
Moderate activity BMR x 1.3
Are constantly on the move with significant amounts of manual labor
(Construction workers, farm workers, and movers are among those who land in this category.)
High activity BMR x 1.4
“Do You Know Your Active Metabolic Rate?” Jillian Michaels. Accessed January 1, 2016.

Using the example BMR calculation from above for a 35 year old 5’9″ woman that weighs 200 lb and has a desk job, the active metabolic rate is 1670 x 1.1 = 1837. She can eat 1837 Calories per day to maintain her weight.

Adjusting Your Calories to Lose Weight

To lose one pound per week, you must have a Calorie deficiency of 3500 Calories per week, or 500 Calories per day.

Using the example active metabolic rate for a 35 year old 5’9″ woman that weighs 200 lb and has a desk job, she would have to restrict her diet to 1337 Calories to lose a pound per week.

IMPORTANT: You should never restrict your diet to less than 1200 Calories. Always consult a doctor or registered dietitian before making changes to your diet or exercise levels.

Considering the Type of Calories

You could technically lose weight by consuming the correct number of empty calories every day. But your body needs more than calories. You need to balance your meals with protein, fat, and carbohydrates. You need vitamins and minerals. You need to maintain your blood sugar levels by eating at the proper intervals throughout the day. Getting healthy is not just about losing weight. You must give your body the proper nutrients.

For more information about getting healthy, see the Getting Healthy Series.

(Unmodified Image: Old-School Kitchen Scales, CC license by Marcus Jeffrey)

Author: Steph

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