Thursday, March 17, 2011

How many calories do you burn every day?

Everybody who's been through 7th grade health class knows that weight loss or weight gain is all about calories in and calories out. If you consume more calories than you burn, you'll gain weight, and if you consume less than you burn, you'll lose weight. Measuring the amount of calories that you take in is easy enough, but how many calories do you burn on a daily basis?

There are a couple ways to measure how many calories you burn every day. The first way to do this is by counting how many calories you consume over the course of a week, then dividing that amount by 7. For example, If I ate 20,000 calories last week, I can divide that number by 7 to estimate my average daily energy expenditure of 2857 calories:

20,000 kcal (weekly calorie intake) ÷ 7 (days in a week) = 2857 kcal daily

Of course, this only works if your weight isn't changing. It also takes a lot of discipline to write down everything (and I mean everything) you eat on a daily basis. However, there is an easier way.

To get a more immediate estimation, it is possible to estimate your average daily energy expenditure by making a few calculations based on your age, gender, weight, and activity level. First, you have to calculate you're resting energy expenditure. This is the amount of calories that you burn every day from bodily functions not related to physical activity, like breathing, food metabolism, and keeping your blood pumping. In order to do that, use one of the following six formulas:

Male, 18-30 years  -  (15.3*weight in kg) + 679
Male, 30-60 years  -  (11.6*weight in kg) + 879
Male, >60 years  -  (13.5*weight in kg) + 487

Female, 18-30 years  -  (14.7*weight in kg) + 496
Female, 30-60 years  -  (8.7*weight in kg) + 829
Female, >60 years  -  (10.5*weight in kg) + 596
(adapted from National Research Council 1989) 

After you've estimated you're resting energy expenditure, you need to use an activity multiplier to account for you're activity level:

very light (almost completely sedentary)  -  1.3*REE
light  -  1.5 - 1.6*REE
moderate (average active person)  -  1.6 - 1.7*REE
heavy  -  1.9 - 2.1*REE
exceptional (lumberjack, roughneck on an oilrig)  -  2.2-2.4*REE
(adapted from National Research Council 1989)

So lets give this a shot. I'm a 25 year old male and I weigh 168 lbs. there are 2.2 lbs in a kg, so 168/2.2=72.37 kg. Next, I have to calculate my resting energy expenditure:

(15.3*72.37) + 679 = 1786 kcal

Now that I have my REE, I have to use one of the activity multipliers to account for my activity level. Right now I'm a student, so I don't get too much physical activity when I'm not exercising (I account for exercise separately). Since I have a light activity level, I'll multiply my REE by 1.6:

1.6*1786 = 2858 kcal

This is my estimated average daily energy expenditure. It's the amount of calories that I'd have to consume every day if I wanted to maintain my current weight. If I wanted to gain weight, I'd have to eat more, and if I wanted to lose weight, I'd have to eat less. These formulas only give a rough estimate of average daily energy expenditure, so it might take a few weeks to hone in on a more accurate estimation.

Lets say I wanted to lose 8 pounds in 8 weeks. How many calories do I need to consume every day? One pound equals 3500 calories, so if I wanted to lose one pound every week, I'd have to create a 3500 calorie deficit ever week. That means I'd have to create a deficit of 500 calories every day.

2858 (estimated daily expenditure) - 500 = 2358 kcal needed to lose approximately one pound every week.

If I wanted to gain weight, I'd just do the opposite by adding 500 calories.

Counting calories works, but just trust me when I say that it is really really hard. If you ask me, counting calories is no way to live. It will help you in the short term, but the only thing that will keep the weight off is to make a few simple lifestyle changes. Just one little change can make a huge difference in your weight, and more importantly your health. For example, you could cut pop out of your diet or start biking to work instead of driving.

Another thing to keep in mind is that not all calories are created equal. Calories come in three different forms: carbohydrates, proteins, and fats. I'd like to take a break from nutrition for a while, but in a couple weeks I'd like to break down the subjects of carbohydrates, proteins, and fats individually. I've been thinking about how and when I'm going to post blogs. I'll try to post a new blog every Saturday morning. Stay tuned!!

1 comment:

  1. Nice article about calorie burn. I was unaware about the regular calorie intake. I was obese for quite a while and cut the carbs from my diet. Instead my weight increased. So, to shed the calories, I tried chi machine. I feel more balanced in my body these days.