Monday, March 16, 2009

BMR 101!

I've gotten quite a few emails from people who are still confused on how to calculate their BMR and figure out how many calories to burn and eat.
We'll use really simple examples...

One pound equals 3500 calories. No matter if you weight 500 lbs. or 150 lbs, 3500 calories burned will always be 1 lb.

Let's pretend my BMR is 1500. So to lose 1 lb. per week, I need to burn 500 calories per day over my BMR, so I want my net calories to be 1000 (Net is calories in (eaten) less calories out (exercise)).

To burn one pound, you can eat your daily 1500 calories and then use exercise to burn 3500 per week (500 calories per day).

Or you can eat fewer calories, like 1300 and burn 200 calories by exercise.

Or you can drop your calories to 1000 and not exercise (NOT RECOMMENDED! this will kill your metabolism unless you have a lot of extra weight.)

Here is the math for eat your BMR and use exercise to lose:
1500 calories eaten
- 500 calories burned by running

= 1000 calories net consumed daily, your body burns 1500, so your net loss is -500
-500 per day times 7 days per week = 3500, which is a pound!

Here is the math for eat less than BMR, and exercise:
1300 calories eaten
- 300 calories from running

= 1000 net calories consumed daily. Body burns 1500, so your net loss is also -500

Say you want to lose 1.5 lbs per week, you need to burn 5250 calories per week over BMR, which is 750 per day. Here's the math for that.

1300 calories consumed
-550 calories burned by exercise

= 750 net calories consumed daily, your body burns 1500, so you're at a net -750 calories lost.
750 daily x 7 days per week = 5250, or 1.5 lbs.

I know I'll confuse some people here, but you can, and should, switch up your days. You don't want to ALWAYS eat 1500 calories and ALWAYS burn 500 calories. Some days you can eat 1300 and burn 300, some days you can eat 1800 and burn 800... as long as you keep your net calories lost each week to 3500, you should lose weight.

Again, that's the math of it all. Your metabolism plays a factor, as does where your calories come from, how much water you drink, how much sodium you consume, and so on... that's why sometimes when you work really hard, you don't see a big loss on the scale. Depending on how active you are, you need to multiply your BMR by 1.1, 1.2, 1.3 or 1.4 depending on your activity. I would consider myself a 1.15, I don't sit ALL day, but I do sit at a desk often. I like to leave out the extra .15 in my BRM as wiggle room for calories over what I think or approximate, and assume that I'll come out even in the end.
But, in the end, if you're doing this the right way (which you are if you're in this challenge), you'll see a loss!


  1. Great explanation!

    I sent you an email earlier today, hoping to join your 20/20 challenge. I hope it's not too late! Please let me know if you didn't get it, my emails tend to get sent to spam.

  2. Thanks for the explanation, very helpful. I'm excited to do this! I know I will be grateful for the accountability. :) I also sent you an email (vintageplum) about joining in. Happy Monday!

  3. could you recommend a good bmr calculator? thanks!

  4. Just curious...isn't it unsafe to eat/burn below 1200 calories a day? I thought that was the bare minimum needed to function.

  5. Thanks for the calculator! I was bummed to find out I should only be eating 1334 calories a day though. It's a good thing I work out most days because I'm pretty darn sure I eat a lot more than that.

  6. OK, I've found my BMR (1480), but most of the calculators I've seen say to also calculate your activity level and then cut calories from that number. Is that what you are doing, too, or do you just use the BMR by itself? Thanks!

  7. susan- a BSc Nutrition graduateApril 15, 2009 at 12:12 AM

    here's the thing:

    BMR is your BASAL metabolic rate, what you need if you do nothing all day. your total energy needs are BMR+TEF+NEAT

    TEF- thermic effect of food (energy used to digest and absorb food) and NEAT- non exercise activity thermogenesis- this is your daily activity including walking places, fidgeting, getting up from a chair etc.

    So, really, you need more calories than just your BMR to maintain weight.

    For example, even if you are sedentary, you need about BMR x 1.2 to maintain weight. The more active you are, the more calories you need.

    I know the goal is to lose weight but BMR is not a good place to start because it is already below what you need to maintain weight daily...going a lot below this could send your body into starvation mode.

  8. Ash,

    Thank you for such clear information! One q you might be able to BMR is 1389 (I weigh 132 lbs.). Should my net be 900, then?

    Thanks! And, great blog!