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Eating below BMR - lack of fuel, huh?

candiceh3
candiceh3 Posts: 379 Member
edited February 5 in Food and Nutrition
So I am trying to work this out.

From what I read, your body can metabolise fat at a rate of approximately 30 calories per pound of body fat per day (correct me if I am wrong?). I thought this was a maximum, but let's use it for the moment.

Let's say your BMR is about 1500 and your TDEE is about 2100.

If you eat below BMR (1200), you have a deficit of 900. However (and this is what really bugs me) your body is getting more than 1200 calories in fuel. Your body is getting 1200 PLUS the fat it can metabolise. So a 170 lb woman with 35% body fat has about 60 lbs of body fat, providing up to 1800 calories a day from fat if required.

So isn't the net fuel used by my body going to be equal to my TDEE? It is not as if eating below BMR equates to your body not getting the fuel it needs. I am literally lugging that extra fuel around with me.

Replies

  • candiceh3
    candiceh3 Posts: 379 Member
    bump ... anyone?
  • LeanneGoingThin
    LeanneGoingThin Posts: 215 Member
    BMR is kind of arbitrary. If you're sedentary, you can usually eat below BMR without much problem.


    I think the main problem is that on a certain amount of calories, you won't get enough micronutrients as they are not in fat. But there are some studies in obese people that do a water fast and take supplements. They wouldn't starve, they wouldn't stop losing weight, but it can be tricky to start eating normally again.
  • nas061
    nas061 Posts: 256 Member
    So isn't the net fuel used by my body going to be equal to my TDEE?

    Yes. But part of that fuel will come from metabolised fat reserves so you will lose weight.

    There's nothing "magical" about your BMR - it is simply your TDEE when activity is zero. People will say "don't eat below your BMR", as if it will not have enough energy to survive. As soon as your calorie intake from food drops below your TDEE your body by definition does not have enough energy for its requirements and therefore it starts to use stored glycogen/fat, and you lose weight.
  • candiceh3
    candiceh3 Posts: 379 Member
    So isn't the net fuel used by my body going to be equal to my TDEE?

    Yes. But part of that fuel will come from metabolised fat reserves so you will lose weight.

    There's nothing "magical" about your BMR - it is simply your TDEE when activity is zero. People will say "don't eat below your BMR", as if it will not have enough energy to survive. As soon as your calorie intake from food drops below your TDEE your body by definition does not have enough energy for its requirements and therefore it starts to use stored glycogen/fat, and you lose weight.

    Yep.

    Those people are annoying!
  • yarwell
    yarwell Posts: 10,477 Member
    So isn't the net fuel used by my body going to be equal to my TDEE? It is not as if eating below BMR equates to your body not getting the fuel it needs. I am literally lugging that extra fuel around with me.

    You are correct. That's why a very fat man could eat nothing for a year and it takes months for hunger strikers to die.

    The whole "eating below your BMR" thing is a piece of MFP nonsense not found elsewhere.
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