If you consume more calories than you burn off, you’ll gain weight, but if you burn off more calories than you consume you’ll lose weight. Sounds pretty basic, doesn’t it? Of course, some experts believe that the quality of calories you take in plays an important role in weight control as well. No doubt, it does! We know that 300 calories of nutrient-dense vegetables have a very different impact on hormones that control your body weight compared to a 300-calorie doughnut.
But, it’s helpful to know how many calories you burn, on average, each day, so you can adjust your daily calorie intake or the quantity of food you take in along with upgrading the quality of your diet. How many calories you expend over a 24-hour period at baseline will vary with your genetic make-up, age, body weight, how much muscle versus fat you carry on your frame, etc.
When considering how many calories you need for weight maintenance, you also have to take into account how active you are on a given day. Obviously, a couch potato with a sedentary job needs fewer calories for weight maintenance than an individual who works as a delivery driver and carries around packages all day and then goes home and exercises. So, how do you know how many calories YOU need to maintain your weight?
There is a useful equation called the Schofield equation that will help you estimate your basal metabolic rate, the calories you burn when your body is completely at rest and you haven’t just eaten a meal or exercised. This is the baseline energy your body needs just to stay alive. It takes a certain amount of energy to support breathing, keep your heart beating, maintain your body temperature, and do other basic physiological processes that keep you alive and kicking. For most people, basal metabolic rate accounts for 60 to 75% of the calories burned each day.
The Schofield equation estimates these basic requirements. In fact, it’s used by the World Health Organization and the U.S. Academy of Nutrition and Dietetics to get an idea of a person’s basal metabolic rate. Once you know how many calories you need everyday baseline, you can multiply an activity factor to roughly estimate how many calories you burn on a given day.
You can use the Schofield equation to estimate your own basal metabolic rate. To calculate your approximate resting metabolic rate, you only need to know your weight in kilograms and use the appropriate formula for your age. Here are the age-adjusted equations:
Age: Formula: (for females)
18-29 14.818W + 486.6
30-60 8.126W + 845.6
>60 9.082W + 658.5
W = weight in kilograms
Of course, your activity level also affects the number of calories you expend in a day too. So, you multiply the value you get above by a factor that approximates how active you are on most days.
Activity Level: (for females): Multiply By:
Very sedentary 1.3
Sedentary 1.4
Light activity 1.5
Moderate 1.6
Heavy 1.9
Very Heavy 2.2
Keep in mind, these equations are for females and there are different ones for males.
Here’s an example. A 40-year-old female who weighs 60 kilograms and is moderately active:
8.126 (60 kilograms) + 487.56 + 845.6 = 1333.16 kilocalories per day
Multiply by 1.7 for activity level:
1333.16 X 1.6 = 2133 calories
The final value 2133 is the number of calories you need to theoretically take in each day to maintain your current weight. Of course, you need to consume less if you’re trying to lose weight.
If you don’t want to calculate the values yourself, there are Schofield equation calculators online, like this one, that will tabulate the results for you.
Estimating Your Activity Level
So, how do you know which activity multiplier to use?
If you have a desk job and don’t do any form of structured exercise before or after work, you fall into the sedentary or light activity category and should use a 1.3 or 1.4 multiplier.
If your job requires that you walk or lift throughout the day and you also do some form of moderate, structured exercise at least three times weekly, you fall into the moderate activity category. In this case, you would use the 1.6 multiplier.
Finally, if you have a very physically demanding job, such as construction work, and do some form of structured exercise outside of work most days, you’re in the heavy activity category. You also fall into this category if you do intense workouts that last an hour or more daily. In this case, use the 1.9 multiplier.
The very heavy activity category would be reserved for a professional athlete or someone who does intense activity several hours per day. This only applies to an elite group of people.
Keep in mind that most people overestimate how physically active they are, so be conservative when you choose how active you are in a given day.
How Accurate is the Schofield Equation For Determining Calories?
The Schofield equation is reasonably accurate for predicting basal or resting energy expenditure in healthy people near ideal body weight. However, studies show that it’s not as accurate for morbidly obese individuals and for people who live in tropical climates Yet, it can give you a rough approximation of how many calories you need daily for weight maintenance if you don’t fall into one of these categories.
Consider Diet Quality Too
Calories are one issue, but if you only consider calories, you could end up harming your health by choosing the wrong stuff. Especially if you’re reducing your calorie intake, the calorie sources you choose should be as nutrient dense as possible. And you can pack lots of nutrients into a meal without adding lots of calories by adding more non-starchy vegetables and lean sources of protein to your plate.
The Bottom Line
The Schofield equation provides an estimate of basal metabolic rate and may not be as accurate in for people in tropical climates and for people who are obese. The most accurate measurement would be indirect calorimetry, measuring how much oxygen you take in and carbon dioxide you exhale as a measure of metabolic rate. But, that’s not always practical. So, the Schofield equation can give you an estimate. Plus, it’s quick and easy to calculate. Try it yourself!
References:
Ann R Coll Surg Engl. 2012 Mar; 94(2): 129–132.
GlobalRph.com. “Determination of the Basal Metabolic Rate (BMR) – Schofield equation”
Hum Nutr Clin Nutr. 1985;39 Suppl 1:5-41.
Eur J Clin Nutr 1991;45:177-85.
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