Before I share ways to calculate your basal metabolic rate (BMR), I think it’s important to highlight reasons why having one blanket number for all women — and, in a sense, differentiating between the genders – is so wrong.
Our body’s caloric needs are dependent upon countless factors – everything from your height to your weight to your age to your muscle mass, all of these numbers matter. They matter because…
1) As you age, your ability to burn calories decreases because, quite frankly, you’re no longer in your teens or early twenties. You’re not “growing” any more. Your body isn’t shutting down, so to speak, but it is coming down off the need to continuously fuel growth.
2) As you build muscle, your caloric need increases. Let’s put it this way. In order for your body to be able to thrive and function, it has to have energy to burn. Carrying different parts of the body requires different amounts of energy. Your body will burn through more calories carrying a pound of muscle than it will in carrying a pound of fat, which is what makes building muscle so necessary for someone coming down from a higher weight who is used to eating more.
3) A 28 woman who is 5’0″, 100lbs needs maybe 1,300 calories total to maintain their weight. A woman who is 6’0″, 180lbs needs approximately 1,600… and that’s not even accounting for muscle mass or activity levels** yet. A sedentary** person who is 5’0″ and 100lbs has no business aspiring to 2,000 calories. That’d put them at a weight gaining rate of almost 2lbs a week. Different sized bodies require different values of calories to maintain their current weight. Part of this is why it’s so laughable to me when people push second and third helpings on their thinner friends, telling them “Go on, eat, eat! You always eat so little!” as if to compare the thinner friend’s plate to their own. Well, no, they don’t require as many calories as you think they might to get by throughout the day. Stop trying to shovel food onto folks. Also, stop comparing your plate to folks who are smaller than you in either height or weight. Your plates shouldn’t look the same… your bodies aren’t the same and don’t have the same needs for maintaining their size.
4) If you are, in fact, that 5’0″ 100lb person and think all women should aspire to 2,000 calories? Chances are, you think simply cutting 500 from that total 2,000 is what you need to do to create your caloric deficit. However, if your basal metabolic rate is only maaaaaaaaybe 1,300 calories, you’re still going to gain weight because you’re not working with the deficit you expected.
The existence of a “recommended daily caloric intake,” for me, is laughable and always has been. It has always felt like a scam – similar to the way the sugar industry tried to get the World health Organization to say that sugar could safely be the source of 20% of one’s calories for the day (which is what it says in the US of A) instead of the 10% it says now – and a way for the food industry to manipulate our perceptions of what our bodies need… which, in turn, results in us NOT reducing our intake… which results in them reducing their profits. There’s a very long blog post in there somewhere, but the reality is that giving off any make-believe foolishness that all of our bodies could firmly maintain that glorified under-200lb ideal that we keep hearing about is nuts.
But, if we know that height, weight, and age all affect how many calories our bodies can burn, then how do we find a formula that accounts for all of those values?
Grab your calculator.
The method that I use goes as follows: 655 + (4.3 x B) + (4.7 x D) – (4.7 x F)*
In that equation, B is the stand in for “your weight in pounds;” D is the stand-in for “your height in inches;” and “F” is the stand-in for “your age.”
So, let’s take the average American woman, 5’4″ and 154lbs. Let’s make her 33. The math would look like this:
655 + (4.3 x 154) + (4.7 x 64) – (4.7 x 33) = ____
Do the math in the parentheses, and you get:
655 + (662) + (300) – (155) = ___
Do a little more math, and you get:
(655+662+300) – 155 = _____
…
1,617 – 155 = 1,462
Your BMR is, then, 1,462.
So…see how different that is from what’s “recommended?” See why any “recommendation” that doesn’t take your specifics into account is harmful?
You also need to factor in your activity levels, as well, though. You have to take into account the intensity of your workouts and how active you are throughout the day:
If you are sedentary every single day (meaning, stay at a desk all day, walk to and from the vending machine or cafeteria or your car, come home sit on the couch), multiply your BMR by 1.2, which would give you 1,754 as your maintenance rate, which means that in order to stay at 155lbs, you’d need to eat somewhere around 1,754 calories.
If you are lightly active, multiply by 1.3. That’d give you 1,900.
Moderately active that day? 1.4 is your magic number, which would give you 2,046 (now we finally break 2,000!) calories.
If you have intense exercise planned that day, then you multiply your BMR by 1.5. This gives you 2,193.
If you’re to the point where you’re training with Pinky and the Brain to take over the world, you’re looking at 1.6, which puts you at 2,339 calories.
How do you cut calories at 1,400 calories, though? You certainly don’t cut a full 500, leaving yourself with only 900 calories to eat each day. This is where exercise becomes so important.
In order to lose 1lb each week, a person simply has to maintain a 500 calorie deficit each day, whereas after seven days the requisite 3,500 calories would’ve been burned. If you cut only 200 – 250 calories and burn the other 250 in moderate exercise, and add lots of veggies in place of some other items to make up for the volume of food you might be missing on your plate, that’s a sustainable rate.
This is also a big part of why, the smaller you become, the harder you have to work if your goal is weight loss. Because the smaller your BMR becomes, the harder it is to sensibly cut calories. At some point, you can’t do it anymore without the exercise. This is also a big part of where weight loss plateaus originate… not checking your BMR as your weight decreases by grand amounts. As your body changes, so do these numbers.
Did I miss anything?
*I know this formula doesn’t account for body fat percentage, but because it’s so hard to get an accurate measure of that without hydrostatic testing, it’d only fudge the numbers more. You can also get a calorimetry test done to determine your real basal metabolic rate. You can also acquire one of those awesome band-y things that’s supposed to measure your calories burned for you… I’ve never used one, but if you’ve got suggestions, let’s hear ’em.
**Added for clarity.