BMI, BMR, Be My Mathematician Please?

Lately, I’ve pursued the frightening task of figuring out my BMR (Basal Metabolic Rate) and what it means to my daily calorie burn and calorie intake. With the help of a friend who is a nutrition major graduate and bariatric nurse in training, I think I’ve figured it out. So, here goes.

What is a BMR?

Your Basal Metabolic Rate, or resting metabolic rate, is the number of calories you need each day to basically sustain life. It’s the number of calories you need to keep up your physiological state. Calculating your BMR (with the help of some formulas) helps you determine the number of calories you need for this upkeep and the number of calories your body burns at rest.

What’s the difference between BMI and BMR?

Your BMI, or Body Mass Index, simply uses your height and weight to determine your body fat. This indicator helps determine if you’re under or overweight, or if you are in the healthy weight range and simply need to maintain your weight. From everything I’ve read, BMI is a good indicator of your body fat percentage and health conditions you may be at risk of due to your BMI, but it’s not a perfect science. Its limitations include the potential to overestimate body fat in people who have a muscular build, and underestimate body fat in those who are older or have lost muscle mass.

Here is my BMI, based on my height and approximate weight, as well as BMI categories (this tool is available at the National Institutes of Health website):

My BMI results

My BMI results

As you can see, I am Overweight – though not by much. A loss of 10 pounds would land me right at 24.9, in the Normal Weight range. Another 10-pound loss would land me safely at a BMI of 23, though I’d prefer to land closer to a BMI of 20.

As stated above, the BMR gets specific about calorie burn and calorie intake, and also takes factors like gender and age into account.

How to Calculate Your BMR

Free BMR formulas and calculators are available for free here.

I used the site’s simple BMR Calculator to determine the following (my BMR is circled in red):

My BMR

My BMR

According to this calculator, I’d burn 1413.7 calories just laying in bed all day. So, what does all this mean when I’m planning my exercise and food intake to lose weight?

First, I need to calculate my daily calorie needs by using the Harris-Benedict equation, which accounts for your BMR and activity level. Here’s the equations:

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Because I am moderately active, I multiplied my BMR of 1413.7 by a factor of 1.55 and got 2191.235. This is the number of calories I can take in to maintain my current weight. Since I want to lose weight, I need to calculate how many calories I need to restrict each day through exercise and calorie reduction.

How many calories to cut and/or burn based on your BMR

To lose one pound a week, I’d need a deficit of 3,500 calories during that week, either through calorie reduction or calorie burn through exercise. That’s 500 calories a day. For a two-pound-a-week weight loss, I’d need a calorie deficit of 1,000 a day.

Sounds like a lot, right? Well, not really, considering that women should take in at least 1,200 calories a day (it’s dangerous to go below this; men need to take in at least 1,800), and deducting 1,000 calories from my Harris-Benedict equation results would land me at roughly 1,200 calories a day. Perfect, considering a 1,000-calorie deficit is as far as most people should go – more than that can be dangerous, especially for people with only a small amount to lose.

Now I just need to make the time to burn off at least 500 calories a day through exercise, and hold fast at the 1,200-calorie-a-day intake. If I do both those things, I should see a 10-pound weight loss in five weeks. Pretty cool, right? These numbers are critical for me to know exactly what needs to be done for a set weight loss goal of at least 20 pounds in 10 weeks.

Resources and Tools:

BMR Calculator

BMI Calculator – from NIH

Calculate BMR with Weight Loss per Week – Livestrong

How to Calculate BMR – Livestrong

Determine Caloric Intake for Weight Loss – Livestrong

Five Things You Need to Know About BMR – Livestrong

MyFitnessPal – track calories burned and calories eaten

Note: The numbers in this post are accurate to the best of my knowledge, and the information contained in this post is explained to the best of my understanding. Depending on the formula/calculations you use, your results may be different. For the most accurate determination of your BMI, BMR, and caloric needs, visit your general physician.

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3 thoughts on “BMI, BMR, Be My Mathematician Please?

  1. Excellent information…BMR is what physicians use to calculate appropriate dosage for chemotherapy in cancer patients. This is information everyone should know about to keep up with activity level and caloric intake, as you are doing….

  2. Interestingly enough – My BMR says I am very overweight and I would have to lose 50 lbs, if I want to be in the “normal” range. That would mean I would have to weigh 100 lbs! I used to weigh between 85 and 95 lbs., when I was in my 20’s and had not had any children. This does not seem healthy or likely at my age of over 40 something! Not sure what to make (or do with) this . . .

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