Basal Metabolic Rate - Help?

McKayMachina
McKayMachina Posts: 2,670 Member
edited September 25 in Health and Weight Loss
I've been researching and trying to understand all the fitness formulas (which is tough because math and I are not pals). But one thing that has always had me totally stumped is Basal Metabolic Rate!

I was reading this very interesting article at http://www.shapefit.com/basal-metabolic-rate.html which defines Basal Metabolic Rate (BMR). It states:

"Your basal metabolic rate, or BMR, is the minimum calorific requirement needed to sustain life in a resting individual. It can be looked at as being the amount of energy (measured in calories) expended by the body to remain in bed asleep all day!"

This is how I've always read/heard it described. Now, depending on which reputable site I visit, my BMR works out to anywhere from 1400 to 2000 calories per day. Some outrageous outliers put it as high as 2500! Let's go with the popular median, 1700, for now:

So my BMR comes out to just over 1700 calories. I've been eating 1700, burning off 500, netting 1200 per day (per MFP).

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What I don't understand is that 1200 calories per day is 500 below my BMR. In other words, I'm netting 29% fewer calories than my "minimum calorific requirement needed to sustain life". How is that possible?! This makes me think BMR is some bullsh*t number that I really don't even need to worry about because, at 3 months in, I'm functioning quite well.

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I've lost 26 lbs., am eating, sleeping and exercising normally and don't feel tired. Hungry? Yes. But keep in mind I ate whatever I wanted in unlimited portions for the last decade. I will likely feel "hungry" for a long while, maybe years, before I adjust to the new habits. (I seem psychologically resistant to change.)

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So, if someone can help me understand a few things, I would GREATLY appreciate it!

1. Is my BMR something I can ACTUALLY find using a formula?
2. If so, which formula should I use? And why?
3. If I eat fewer calories than my BMR will I become ill/weak or die?

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My specifics, in case anyone needs them to help further:

- Current weight: 209
- Goal weight: 135
- Age: 26
- Height: 5' 2"
- Lifestyle: Sedentary - I work long hours at a desk. (does not include bursts of exercise which are logged separately for calories burned)

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Is it that my body is burning fat for fuel and getting the rest of its BMR needs from there? Is that how this (weight loss) works?

THANK YOU FOR ANY HELP!!!

Replies

  • LYNNPETTY93
    LYNNPETTY93 Posts: 61
    Here is your formula
    English BMR Formula
    Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) - ( 4.7 x age in years )
  • jms023
    jms023 Posts: 37 Member
    Well, to answer one of your concerns, the BMR is the minimum amount of calories needed for you to survive. Your calorie deficit of 500 calories does not mean that you are not getting those calories. It means you are not ingesting them. The calories to fill in the deficit are coming from fat. That is how you are losing weight--the body is not getting the calories it needs to survive from outside sources (food) and is thus using its energy stores (fat) to get the remaining calories it needs. Hope that clears it up a little!
  • McKayMachina
    McKayMachina Posts: 2,670 Member
    Here is your formula
    English BMR Formula
    Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) - ( 4.7 x age in years )

    Yes, thank you. That puts me right at 1700. I'm still confused on the other points.
  • McKayMachina
    McKayMachina Posts: 2,670 Member
    Well, to answer one of your concerns, the BMR is the minimum amount of calories needed for you to survive. Your calorie deficit of 500 calories does not mean that you are not getting those calories. It means you are not ingesting them. The calories to fill in the deficit are coming from fat. That is how you are losing weight--the body is not getting the calories it needs to survive from outside sources (food) and is thus using its energy stores (fat) to get the remaining calories it needs. Hope that clears it up a little!

    It does! Thx! This has been my thinking, as well. :)

    Now, if only I knew which BMR formula was correct!
  • LYNNPETTY93
    LYNNPETTY93 Posts: 61
    Here is your formula
    English BMR Formula
    Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) - ( 4.7 x age in years )

    Yes, thank you. That puts me right at 1700. I'm still confused on the other points.

    Some people drop them, and some round them up. I drop mines and go to the next number.
    Mines is 1577 but that's some bull if you ask me.
    I wear a HRM and my burn for 10 hours of wear is now 2860 so it has to be BS and only burned 525 with workouts today..
    It's good to know where you stand, but I would not put to much thought into this. You know you are eating more than a 1000 calories.. So why worry.. 1200 is good enough to maintain day to day task...
  • georgiajuly
    georgiajuly Posts: 126
    1. No. It can only be estimated, outside a lab where the pertinent variables can be measured.
    2. Sorry, I don't have time right now to track that down. Perhaps an expert can help on that.
    3. Not necessarily. The definition you cite is flawed. The Wikipedia definition is "the amount of daily energy expended by animals while at rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans). " How long the animal can survive on stored calories (for example, a hibernating bear) depends on a number of other factors, one of which is how many stored calories there are.
    4. Moreover, I don't recall MFP referring to BMR in goal setting. They refer to "calories burned from normal daily activity", which assumes that some of us actually get out of bed every day, even if we don't do much once we get there. My estimate is 1760, which would be higher than my BMR.

    Hope this helps.
  • LYNNPETTY93
    LYNNPETTY93 Posts: 61
    I think you have every right to be concern about your BMR. Keep up the good work.
  • toodleton
    toodleton Posts: 82
    The whole point to knowing your BMR is to create a deficit either by reducing caloric intake with food or exercise,,,,,the only way to lose weight is to create a deficit. If you -500 a day then after 7 days=3,500....1 pound consists of 3,500 calories
  • LarryPGH
    LarryPGH Posts: 349 Member
    Here's the problem, though...

    You're *not* maintaining a 500 calorie a day deficit... see, your body doesn't burn 1700 calories a day. You identified that you have a sedentary lifestyle, which means that your body burns 25% more than just lying in bed all day. In other words, your body burns 2125 calories a day, plus whatever you add in exercise.

    So, you're at a 925 calorie-a-day deficit! That means that you're shooting for nearly two pounds a week weight loss! That's not terribly unhealthy, if you're up around a 32 BMI or greater -- but if you're in the 30 BMI range, that's waaaaay too fast!

    Edited to add: and, if you're doing 500 calories of exercise a day, you're really talking about a 3 pound per week weight loss goal -- unless you're way up there on the BMI scale, that's not a healthy or sustainable approach, even in the short term!
  • McKayMachina
    McKayMachina Posts: 2,670 Member
    Thank you, everyone, for the great info. I feel like I have a more complete understanding now. :)
  • AlaskaAngel
    AlaskaAngel Posts: 1
    Can somebody help me out here by explaining it using the terms that MFP uses?

    These are the numbers for me:

    Totals 1202
    Your Daily Goal 1676 (What does this number mean? Does it mean that to lose 2 pounds a week I must eat at least this much?
    The more I exercise, the higher this number gets. So why would my goal be to eat as much as I'm exercising?
    Remaining 474

    Thanks for any help.
  • bcdg24
    bcdg24 Posts: 35 Member
    Thanks for posting this topic, McKayMachina! I have been wondering the exact same thing and am so glad someone posted so i didn't have to!

    I will make a bold statement and say MFP's calculations are just too calorie conservative. Using the formula that LYNNPETTY93 posted, my BMR is 112.15 calories higher than what MFP has calculated.

    I also have a desk job, so I said i have a sedentary lifestyle. I really appreciate the knowledge that a Sedentary Lifestyle is 25% more calories burned/higher activity than the BMR; MFP calculates my daily calories burned currently at 1880/day; but if I use the BMR calculated with the formula posted earlier x 1.25, my daily calories burned would be 2016. If I'm only eating 1200 calories per day, that is a weight loss goal of 1.6 lbs per week, when i have set my goal for 1.5 lbs per week.

    Further compounding the issue, I dont only sit at a desk all day; I have two very young children, so i am chasing them around the house, lifting them, and carrying them intermittently for at least 4.5 hours each day Mon - Thur and most of Friday afternoon, and all day Saturday and Sunday. At work, I get up frequently to refill my water and go the bathroom, and at least twice a day to talk to coworkers in other departments, at the other end of the building. Should I then say I have a lightly active lifestyle, even though I have a desk job?

    I am wondering about all this because instead of losing 1.5 lbs per week, I have lost an average of 4 lbs in my first three weeks. So maybe I, too, need to readjust my goals...
  • baisleac
    baisleac Posts: 2,019 Member
    http://www.myfitnesspal.com/topics/show/217700-confused-about-bmr-tdee-and-deficit-how-many-calories-you
  • Atlantique
    Atlantique Posts: 2,484 Member
    Can somebody help me out here by explaining it using the terms that MFP uses?

    These are the numbers for me:

    Totals 1202
    Your Daily Goal 1676 (What does this number mean? Does it mean that to lose 2 pounds a week I must eat at least this much?
    The more I exercise, the higher this number gets. So why would my goal be to eat as much as I'm exercising?
    Remaining 474

    Thanks for any help.

    I assume you set your goal at a 2lb per week rate of loss?

    Your daily goal is calculated this way:

    (BMR calories + Activity Level calories) - 500 calories per day = Your Daily Calorie Goal.

    MFP is calculating a consistent calorie deficit for you even if you never exercise.

    On days that you log exercise, MFP calculates your goal this way:

    (BMR calories + Activity Level calories + Exercise Calories) - 500 calories per day = Your Daily Calorie Goal.

    MFP expects you to eat your exercise calories back because they've already built a calorie deficit into your daily goal. eating your exercise calories keeps that goal consistent.

    Exercise is meant to preserve lean muscle mass, reshape your body and improve overall strength and fitness. It's not really used as a way to create calorie deficits on MFP.

    *Note* that on MFP, "Activity Level" only represents your 8 hr workday. It does NOT include purposeful exercise, which is why you log your exercise as you perform it.
  • Leigh_D
    Leigh_D Posts: 356 Member
    * BUMP *

    Here is my $.02 that is basically agreeing with everyone:
    I attended a seminar on nutrition where Basal Metabolic Rate was all spelled out. I had never heard of it before! It's been magic for me. Since following this, I've lost about 45 pounds and counting! Let's take the calculation and figure it out, long-hand for a woman 5'3", 29 years old, currently 200 pounds:

    655 + (4.35 x weight in pounds) + (4.7 x height in inches) - (4.7 x age in years)

    655 + (4.35 x 220) + (4.7 x 63) - (4.7 x 29)

    655 + 957 - 136.3

    1476
    (I'm rounding to whole numbers now.) This is Basal Metabolic Rate -- the amount of calories (energy) you need just to run your body, like your heart and brain and breathing.

    Now, it doesn't end there! There are a couple of modifiers! That is the BASAL rate, which means "base" or "basic" like fundamental. But you move around in the day, and that takes energy too. So we need the modifier called "Harris Benedict Formula". For most of us we take that BMR number and multiply it by 1.2 (an increase of 20%). MFP does this when you sign up and you choose the little button for daily average activity level.

    1476 x 1.2 = 1771

    NOW we have not just the "base" number, but the daily calorie needs to maintain. But we don't want to maintain our current weight! We want to tap into the stored energy in our body and reduce the extra pounds. So now we want to run a modest deficit off that number. The calories (energy) in one pound of fat is 3500. To lose one pound a week, divide 3500 calories by 7 days a week = 500 calorie per day deficit.

    1771 - 500 = 1271

    So, this woman's daily calorie budget to lose one pound a week is 1270.

    When you exercise, do your best to get an accurate calorie count (because it also varies on age/weight/height) and you get to eat that many "extra" calories that day! The reason is you are already running a deficit off the calorie needs for your body. When you burn calories in exercise, that takes away from the energy available to your body for the rest of its functions and they should be (mostly) replaced.

    So don't be "afraid" to eat! Food and calories are not the enemy! Just most of us have to learn all over again how to eat for FUELING our bodies, not stuffing. I know I have!

    Again, I am not some kind of genius! I learned all of this in a nutrition seminar from a registered dietician. I am happy that MFP follows the same formula.
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