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Energy from carbs and fats - interchangeable?

yirarayirara Member Posts: 6,698 Member Member Posts: 6,698 Member
This is something I've been wondering. I'm sure there's an explanation but I can't find it.

When you go on a tempo run and most, if not all of your energy comes from glycogen. Back home you have a tea, then go to bed. Do you lose bodyfat or did you only deplete your glycogen stores until the next morning? I'd think it doesn't matter much: you also burn energy when sleeping, and this will be mostly from fat and protein sources. Though the amount is likely a lot less than from the run. What I'm aiming at is how interchangeable energy sources are. If you do tempo runs for whatever reason every night to create a calorie deficit (I'm sure those crazy people are out there) would you lose bodyfat at the same rate as just having a calorie deficit of the same calorie amount?
edited June 2

Replies

  • xrj22xrj22 Member, Premium Posts: 66 Member Member, Premium Posts: 66 Member
    For weight loss, a calorie deficit is a calorie deficit. If you have a calorie deficit, you loose weight regardless of what form of calories you are eating or burning. There is a slight tweak to that concept if you are eating very low carb, and glycogen stores are depleted. Then your body burns a few more calories that what you would compute because converting fat to glucose uses energy (calories).
  • neanderthinneanderthin Member Posts: 7,775 Member Member Posts: 7,775 Member
    xrj22 wrote: »
    For weight loss, a calorie deficit is a calorie deficit. If you have a calorie deficit, you loose weight regardless of what form of calories you are eating or burning. There is a slight tweak to that concept if you are eating very low carb, and glycogen stores are depleted. Then your body burns a few more calories that what you would compute because converting fat to glucose uses energy (calories).

    Fat isn't converted to glucose but is used as the substrate for gluconeogenesis which uses glycerol, amino acids, lactate and a couple others, don't remember to produce glucose in the absence of glycogen or carbs between meals.
  • ninerbuffninerbuff Member, Greeter Posts: 45,623 Member Member, Greeter Posts: 45,623 Member
    Endurance athletes work on adapting their bodies to use fat as energy. However, the conversion is quite slow which is why when an endurance athlete totally deplete glycogen levels and hit "the wall", they can't move anymore. There isn't enough time for fat to get converted to energy in this scenario.

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  • janejellyrolljanejellyroll Member Posts: 25,871 Member Member Posts: 25,871 Member
    tsazani wrote: »
    "Beating the wall."

    Isn't that the reason endurance athletes use the MAF Method, 80/20, or other low intensity training methods?

    I'm going to try 8 weeks of exercising for 1 hr a day at 60-70% MHR. See what happens? I'd like to lose 2 inches on my waist.

    I may be missing the point, but an hour of activity isn't enough to really test any theories about glycogen depletion or utilizing fat as energy for endurance activities, is it?
  • heybalesheybales Member Posts: 19,174 Member Member Posts: 19,174 Member
    tsazani wrote: »
    "Beating the wall."

    Isn't that the reason endurance athletes use the MAF Method, 80/20, or other low intensity training methods?

    I'm going to try 8 weeks of exercising for 1 hr a day at 60-70% MHR. See what happens? I'd like to lose 2 inches on my waist.

    What will happen is your HR during the activity will likely lower as you improve your mitochondria and enhance fat usage, needing less oxygen for lessened glucose usage.

    Which means when you do a truly endurance activity where total usage of glucose could occur - you'll have more time before that wall is hit.
    Or in the same manner, go a tad faster before using up those stores in the same amount of time.

    Now - if just starting out exercising too and a tad unfit, you'd have a lowering of HR no matter how you did it.

    The MAF test really only works for a comparison if already fit, just training subsystem improvement. Which actually can be improved in just 60 min, but keep adjusting the pace to hit the HR desired - and hopefully be summer heat kicks in and requires increased HR merely for cooling effect.

    And the fat will be supplied from that existing in the blood flow and nearby or intra-muscular sources, not your waist unless you are doing endurance situps somehow.

    Your waist will be reduced from being either in a general calorie deficit, or eating at maintenance and progressive lifting.
    edited June 2
  • NorthCascadesNorthCascades Member Posts: 10,662 Member Member Posts: 10,662 Member
    tsazani wrote: »
    "Beating the wall."

    Isn't that the reason endurance athletes use the MAF Method, 80/20, or other low intensity training methods?

    I'm going to try 8 weeks of exercising for 1 hr a day at 60-70% MHR. See what happens? I'd like to lose 2 inches on my waist.

    Hitting the wall, or bonking. You don't beat it like shadow boxing, you run into it and crash.

    The reasons many enduros follow a regime where most of their training sessions happen at relatively low intensity are (1) it works, as evidenced by the fact that the fittest humans on earth train this way, and (2) to be recovered enough to be able to do the hard sessions while maintaining a high volume. But the key word is relative, what counts as "low intensity" for one person can be an unsustainable workload for another.

    % of what you think is your max heart rate doesn't mean very much.

    Calories in and out will affect your waist, bonking not so much. It'll just feel like a sudden and overwhelming sense of "*kitten* the world, I'm done here."

    🙂
  • naomi9271naomi9271 Member Posts: 127 Member Member Posts: 127 Member
    Bonking....that brings back memories. Done that once, very unpleasant experience, on a long-distance bike ride. Pedaled the last mile at around 4 mph, could not move more, felt like death. It’s not something you deliberately want to strive for.
  • yirarayirara Member Posts: 6,698 Member Member Posts: 6,698 Member
    naomi9271 wrote: »
    Bonking....that brings back memories. Done that once, very unpleasant experience, on a long-distance bike ride. Pedaled the last mile at around 4 mph, could not move more, felt like death. It’s not something you deliberately want to strive for.

    Oh, bonking is normal for me. Also happens when I sacrifice carbs for protein and fats. It’s nice when you’re on a 3 week vacation to a country where carbs are mostly reserved for locals (free/subsidized bread and rice, veggies from garden) and the handful of tourists get lots of meat and fatty stuff. No, I didn’t get used to it.
  • jjpptt2jjpptt2 Member Posts: 5,419 Member Member Posts: 5,419 Member
    tsazani wrote: »
    "Beating the wall."

    Isn't that the reason endurance athletes use the MAF Method, 80/20, or other low intensity training methods?

    I'm going to try 8 weeks of exercising for 1 hr a day at 60-70% MHR. See what happens? I'd like to lose 2 inches on my waist.

    I may be missing the point, but an hour of activity isn't enough to really test any theories about glycogen depletion or utilizing fat as energy for endurance activities, is it?

    That was my thought, too.
  • heybalesheybales Member Posts: 19,174 Member Member Posts: 19,174 Member
    An hour a day is actually enough time to cause changes.
    No, you won't be experiencing the wall, or pushing to the limit - neither of which is required to improve when depletion occurs. The improvement comes from burning more fat at same level of intensity, sparing the carbs.
    HR is an easy proxy for what intensity you are at.

    To make it even faster for improvements, make it 2 hrs a day, according to the next study (which comments on the 1 hr improvement too).

    While this study is more focused on the fact burning more fat during the exercise doesn't change the overall daily burn - it does highlight some of the responses being discussed for improving the endurance.
    And why it happens, and several other things mentioned.

    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2885974/

    Though - elite marathoners with their training are a different story than recreational I recall.
  • viajera99viajera99 Member Posts: 248 Member Member Posts: 248 Member
    cwolfman13 wrote: »
    My wife did a marathon in Lisbon a few years back with her sister. She bonked hard...she thinks about 15 miles in, but she's not entirely sure where she stopped. She doesn't remember a lot, but she sort of remembers vomiting a lot and somebody in a golf cart picking her up and dropping her off at her hotel where she collapsed in the lobby and woke up in the hospital.

    That sounds a lot worse than mere glycogen depletion. It sounds more like heat exhaustion or severe hyponatremia.

    Scary story and glad she's OK!
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