I read recently that, for someone who is keto-adapted, different forms of exercise rely of different bioenergetic systems. HIIT relies primarily on muscle glycogen/glucose, whereas less intense workouts(such as jogging) rely on ketones and fatty-acid oxidation. Is this a rule that the more intense the exercise, the higher proportion of energy comes from glycogen/glucose? Or does it also depend on the type of exercise?
In other words, what are the factors which decide whether the body uses fats(ketones/fatty acids) or sugars(glycogen/blood glucose) for energy(aside from keto-adaptation)?
asked byRoryD (623)
Get FREE instant access to our Paleo For Beginners Guide & 15 FREE Recipes!
on April 20, 2013
at 01:35 PM
The intensity determines whether or not you use fat or glucose for energy. When you are doing very high intensity exercise, your body cannot convert fat into energy quickly enough, so glucose is used. That is, by definition,what makes it glycolytic.
When you are doing lower instensity work, your body will burn the majority of its energy as fat, but fatty acids will be mobilized at a slower, more steady rate.
However, that does not mean low intensity work burns more fat overall. When you are doing HIIT, lactic acid builds up in your muscles and you must recover between bouts. During your bouts of recovery you are actually going to burning a combination of fat and glucose. Likewise, when you are doing low intensity work, you will again be burning a combination of the two, because glucose has other uses besides just fueling glyocolytic workouts. In the long run, you will definitely burn more fat doing glyocolytic workouts as opposed to low intensity workouts because a lot of glucose consumption will be diverted into glyocogen storage, and a lot of free fatty acids are quickly mobilized while doing HIIT, which will get gradually burned off in the hours after the completion of your workout. Your muscle cells will be more insulin sensitive and your fat cells less so you'll be one step closer to creating the ideal hormonal environment for fat loss and muscle gain.
This also seems to be where there is a bit of confusion. If you run very long distances (i.e. marathoner), then in reality it would make more sense to eat a diet high in fat and protein. Conversely, if you are doing glycolytic work (HIIT by defintion) in the form of weights and/or sprints and/or plyometrics, then it makes more sense to be eating a higher protein, moderate carb, moderate fat diet. Never a low carb diet (except for short durations if you are about to compete in a fitness modeling competition)
on April 20, 2013
at 01:28 PM
This is a great question Rory. Your basic premises in your first paragraph basically appear to be correct and the correct conclusion is that the more intense the exercise, the higher proportion of energy comes from glycogen/glucose/the anaerobic process of your cells.
Watch http://www.youtube.com/watch?v=2PdJFbjWHEU&feature=youtube_gdata_player from 1:02:40 onward and he will literally answer your exact question formally.