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I asked this recently in the comments section of another topic. I was hoping to get more feedback so here it is in official question form.

Many within the Paleo community recommend high fat/low carb in order to become a fat burner which is better for longevity. I can totally buy this.

BUT, many within the same circle recommend short duration but high intensity sugar burning exercise. Some claim that what you burn during exercise you burn the opposite at rest (JJ Virgin also Jade Teta from Metabolic Effect). I don't know if this is true.

WHY is burning fat good when it comes to diet, but burning sugar is good when it comes to exercise?

(I just want to add that what I am trying to figure out is what caused me to crash during my low carb high fat HIIT days).

EDIT: I realize that I did not word this well. By sugar burning exercise I mean intervals, sprinting, short duration high intensity stuff as opposed to fat burning exercise which is done at a more moderate level.

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I've been thinking along the exact same lines, and I admit that I'm mighty confused about this dichotomy. – smcdow Sep 1 2011 at 17:20

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My comment below assumes you are not training hard for a triathalon, or to build lots of muscle mass...

I thought the point was to occasionally-- once a week or so-- do some short-duration full-out exercise to ensure your body's native glucagon gets burned up, thereby forcing your body into gluconeogenesis wherein it uses stored body fat to replenish those glucagon stores in the liver and elsewhere.

The idea that if you're training intensely, and eating hardly any carbs at all, you may go into ketoacidosis, which is bad news. But if you're like me, and don't get enough exercise, forcing your body into gluconeogensis to burn extra fat is a good thing. Assuming, of course, that you're also like me and you have the adipose tissue to burn.

UPDATE: To Cliff, below (threaded comments not working)

It is true that gluconeogensis occurs using certain amino acids deriving from protein. It is also true that it uses glycerol, which comes from triglycerides and the fat in our tissues.

So we are both right.

I was under the impression, though, that the process you're talking about, Cliff, was more prevalent in ketoacidosis, which will only happen in extreme cases in those that aren't diabetic. The byproducts of that result include-- I hear-- one's breath smelling of nail polish. Which certainly sounds like something I would like to avoid.

Because of your observation, Cliff, we always should ensure we are eating enough protein. But if a person is on this board they almost certainly are eating enough protein.

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A small correction- it's glycogen, not glucagon. Glucagon is a hormone. Ketoacidosis is a metabolic state that healthy people don't have to worry about (it mainly occurs in Type 1 diabetics) although I have heard that VLC + intense training can cause elevated cortisol. – Olivia Aug 31 2011 at 2:48
Thanks for that correction. I always mixed those up in Nutrition class! – karlub Aug 31 2011 at 3:03
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gluconeogenesis burns protien not fat, fat can not be turned into glycogen – cliff Aug 31 2011 at 10:44
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your right about glycerol, totally slipped my mind. Glycerols are just the backbones of triglycerides though and are not fatty acids. If your gonna do glycogen depleting exercise you would be better off with extra carbs not protien imo – cliff Aug 31 2011 at 11:55
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Don't forget that beta oxidation (fat burning) can supply ATP up into fairly high heart rates if you are properly fat adapted. – Jeff Aug 31 2011 at 13:46
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I don't recommend glycolytic exercise for fat loss because it increases the glycogen repletion burden that has to either come from an increase in dietary carbohydrate (which will interfere with satiety and insulin levels) or from gluconeogenesis, which could be catabolic or at best create a lot of ammonia from protein breakdown. Cortisol levels would have to increase dramatically if one were doing LC + weight training and/or sprinting. I think it's bad advice to advocate either of these for fat loss, and terrible advice to recommend that they occur together.

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Is glycolytic exercise something like sprinting? – Cacktus Wayfinder Aug 31 2011 at 1:50
Thanks you. I appreciate this answer. This makes a lot of sense to me. I can't figure out why low carb is so often paired with this type of workout. @Chapa - yes I did mean sprinting, HIIT, all sorts of intervals. – none Aug 31 2011 at 2:12
So, this sounds like an either-or situation: Either you go for fat-burning and longevity via LC, or you go for HIIT performance by adding carbs. But, you can't do both at the same time? I won't argue the point, but this just doesn't feel correct to me. – smcdow Sep 1 2011 at 17:25

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