The Math of Weight Loss

And why it sometimes doesn’t work…

Physical fitness has mattered to me for one reason or another for the better part of forty years.  Ever since I was in high school running track, playing soccer, wrestling… I needed to be in shape. When I enlisted in the Army fitness was mandate and part of the promotion process. On the police department fitness may well have meant the difference between life and death in a fight for your life. It more often meant the difference between whether or not you could catch the suspect running away from you. What does all that have to do with the Math of Weight Loss?  Hang with me, I’m getting to that.

For too many people, “being fit” simply means “not being overweight.” There is a difference, but weight definitely plays a significant role in your overall fitness level. If you’re grossly overweight or dangerously underweight, your body cannot function properly. There are common ailments that seem to accompany either extreme and they should be avoided. As you read the following, please understand that it is a general guideline and does not strictly apply under all circumstances. Every individual’s fitness program and journey is, or should be, as unique as they are.

That all said, weight loss or gain can be viewed as a simple math equation. To understand the equation, we have to know a few things first. The first and probably most important thing we each need to know is our own Basal Metabolic Rate or BMR. This is often misstated as “Basic” Metabolic Rate. It doesn’t really matter how you say it as long as you understand it. YOUR BMR is how many calories it takes for your body to maintain its current weight if the only activity you undertake is involuntary muscle function, eating, voiding waste and sleeping. There is a formula for figuring out what your BMR is, as described below.


W= Weight in Pounds     H= Height in inches     A= Age


655 + (4.364 x W) + (4.25 x H) – (4.7 x A) = BMR


66 + (6.227 x W) + (10.5 x H) – (6.8 x 54) = BMR

Those formulas – one for men and one for women – give you an unadjusted BMR. The adjustment you need to make is for your daily activity. Most of us have a way of overestimating our actual activity while, if your goal is weight management or loss, your goal should be to under estimate your activity (if anything).  To adjust your BMR for activity, use the following.


BMR x DA = TOTAL CALORIES (per day with no weight loss or gain)


Very light- x1.3         (No exercise, sitting, standing, watching TV)

Light- x1.5                 (Walking, yoga, light exercise)

Moderate- x1.75       (Daily exercise, weight training, running)

Heavy- x2                  (Athletes, training/working out more than 2 hours a day)


66 + (6.227 x 205) + (10.5 x 70) – (6.8 x 54) = BMR

66+ 1,277 + 735 – 367.2 = 1,710.8

I “run” for a minimum of 30 minutes per day on my elliptical but spend a lot of the rest of my time sitting at my desk. My primary occupation is performed on a computer so I consider myself at the “Very Light” end of Daily Activity.  Multiplying my BMR by my DA is… 1,710.8 x 1.3 = 2,224. That is my ADJUSTED BMR.

That 2,224 is the number of calories per day to maintain my current weight of 205.  That’s the first part of the math we need to understand. Here is the rest of it.

One pound equals 3,500 calories. So if you want to gain a pound you need to take in 3,500 calories MORE than your adjusted BMR. If you want to lose a pound you need to take in 3,500 calories less than your adjusted BMR.  VERY few people take in that many calories in a day, so it’s easier to think about it over the period of a week… seven days. If you want to gain a pound per week, eat an extra 500 calories per day. If you want to lose a pound per week, eat 500 calories less per day than your adjusted BMR.

But the math also has to include exercise because that burns calories. So if your adjusted BMR is 2,224 like mine, but you want to lose weight – say one pound per week – you have to have a NET intake of 1,724 calories per day; 500 less than your adjusted BMR. To accomplish that I can either eat 500 calories less OR I can eat the 2,224 and exercise off 500 calories each day. Another option would include eating 3,000 calories per day but then exercising off almost 1,300 calories to get me back to a daily net caloric intake of 1,700.

In my case I do a mix of limiting intake and exercising off calories. I aim for a reduced calorie intake of approximately 1,720 calories per day. Additionally I exercise on my elliptical for 30 minutes which I take a calorie credit for of 10 calories per minute or a total of 300 calories. So, theoretically I could eat 2,020 calories per day, exercise off 300 and still have a NET calorie intake of 1,720. That’s 500 calories under my adjusted BMR so in a week I should have a deficit of 3,500 calories… or one pound.

Now… if the math is that simple, how come some people short their intake in big ways, exercise a ton and then don’t lose the weight they think they should be?  There can be a couple reasons.

One of the most common is a higher than average sodium (salt) intake in spite of the overall food intake reduction. Salt helps your body hold water and water weighs 8 pounds per gallon. So if your body holds just one extra PINT of water, that’s an extra pound of weight.

Another is that if your body starts to perceive starvation… common if you have a net calorie intake under 1,200 calories per day, it tries to store every calorie it can as a fat calorie. This is most easily done if you don’t eat breakfast, don’t eat lunch and then eat a small dinner. Every calorie you take in at dinner your body is trying to hold onto and it’s NOT building any muscle mass; it’s holding those calories as fat everywhere it can. This is NOT a healthy way to try to lose weight.

The last most common reason why you might have a calorie deficit OR be breaking even but seeing weight GAIN is this: muscle weighs more than fat. If you’re eating a clean and healthy diet while exercising, your body sheds fat and increases muscle mass (if your exercise regimen includes strength training of any kind). So while you might lose inches of fat, you gain weight in muscle. This is the perfect example of why weight loss or gain should not be the sole indicator of your overall health increase or decrease.

Weight management, whether gain, loss or simple maintenance, is only one indicator of health. Some performance measurements you should consider include strength, endurance and flexibility. Physiological health indicators you should stay aware of and maintain through proper nutrition combined with exercise are blood pressure, resting pulse rate, blood sugar levels and respiratory rate. Look for more about those in the future!

As a final note on BMR, as you can see from the image used in spite of the calculations described, there are several formulas from various authorities to calculate BMR and Adjusted BMR. Each authority claims that theirs is the most accurate. Pick whichever one you choose and stay with it, adjusting your nutritional intake and exercise levels as necessary to get the results you’re looking for.


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