Metabolising carbohydrates when fat/keto adapted?

[LittleGreyCat]

I think this belongs here not in the exercise forum.

If you are low carb or keto, your main energy source is ketones.
Your body makes any glucose required by parts of your body, and maintains normal BG levels (we wish).

So what happens if you eat enough carbohydrates to exceed the basic metabolic requirement, but far too low to meet energy requirements?
You are still burning mainly ketones, but there are some spare carbohydrates floating around.

Anyone know the science of this?
Does it get burned slowly by the body (e.g. brain) and loaded into the tissues but not generally used for energy by the muscles?
Does it get used preferentially?

I started searching for information and came across carb cycling.
Then found a thread here.
https://www.diabetes.co.uk/forum/threads/carb-cycling-my-most-dangerous-diet-plan-attempt.183780/
There seems to a a premise that you can load up your muscles with glycogen before exercise without disturbing the main keto metabolism but providing that extra bit of boost during exercise.

https://www.dietdoctor.com/low-carb/carb-cycling
[Pretty good thread to read IMHO.]
says
"In an effort to prolong the time to muscle fatigue during competitive exercise, loading up with carbohydrates prior to the event is thought to replenish muscle glycogen stores, while not significantly changing the body’s adaptation to increased fat oxidation. Therefore, a fat-adapted athlete should be able to efficiently burn fat during exercise, tapping into muscle glycogen stores only when needed (likely during the most intense intervals of exercise)".

There seems to be very little strong evidence either way.
I do have a strong temptation to try some carbohydrates half way through my weekly group cycle ride as I have a good stock of Libre results where I just have coffee.
I have (probably very obviously) less energy on the second half of the ride and am wondering if a few carbs could provide a quick energy boost later in the ride.

One final confusing bit is that at the start of the ride my liver seems to dump lots of glucose into my bloodstream which isn't instantly used.
This suggests that either it is a lot of glucose or that I am not metabolising glucose in preference to ketones.

Anyway - cake!

 

[NicoleC1971]

From what I know the endurance athlete who is fat adapted burns fat in the absence of available glucose but for explosive power /sprint type exercise (don't know what your group cycle class is like but they can have power hills and fast sprint intervals so may qualify!) the athlete may benefit from having some 'rocket fuel' without incurring metabolic damage.
You don't need to carb load if you are fat adapted but if you are going to enjoy some carbs I'd recommend after the ride as the optimal time because this is when the body will see to replenish the glycogen (glucose in muscles) so hopefully your blood sugar/insulin would not spike excessively because the extra carb has a home to go to!
As for the liver dump at the start this is your stress hormones asking for extra fuel!
Tim Noakes or Steve Phinney and Jeff Volek have probably detailed the actual mechanics of this somewhere as this is the main topic of their research in the case of Phinney and Volek.

 

[Trevor vP]

I think this belongs here not in the exercise forum.

If you are low carb or keto, your main energy source is ketones.
Your body makes any glucose required by parts of your body, and maintains normal BG levels (we wish).

So what happens if you eat enough carbohydrates to exceed the basic metabolic requirement, but far too low to meet energy requirements?
You are still burning mainly ketones, but there are some spare carbohydrates floating around.

Anyone know the science of this?
Does it get burned slowly by the body (e.g. brain) and loaded into the tissues but not generally used for energy by the muscles?
Does it get used preferentially?

I started searching for information and came across carb cycling.
Then found a thread here.
https://www.diabetes.co.uk/forum/threads/carb-cycling-my-most-dangerous-diet-plan-attempt.183780/
There seems to a a premise that you can load up your muscles with glycogen before exercise without disturbing the main keto metabolism but providing that extra bit of boost during exercise.

https://www.dietdoctor.com/low-carb/carb-cycling
[Pretty good thread to read IMHO.]
says
"In an effort to prolong the time to muscle fatigue during competitive exercise, loading up with carbohydrates prior to the event is thought to replenish muscle glycogen stores, while not significantly changing the body’s adaptation to increased fat oxidation. Therefore, a fat-adapted athlete should be able to efficiently burn fat during exercise, tapping into muscle glycogen stores only when needed (likely during the most intense intervals of exercise)".

There seems to be very little strong evidence either way.
I do have a strong temptation to try some carbohydrates half way through my weekly group cycle ride as I have a good stock of Libre results where I just have coffee.
I have (probably very obviously) less energy on the second half of the ride and am wondering if a few carbs could provide a quick energy boost later in the ride.

One final confusing bit is that at the start of the ride my liver seems to dump lots of glucose into my bloodstream which isn't instantly used.
This suggests that either it is a lot of glucose or that I am not metabolising glucose in preference to ketones.

Anyway - cake!

For endurance athlete longer than 5 hours we teach our bodies to burn fat if we are fat adapted and want to try stay low carb.

That means lots and lots of training in what they call Z2 (low heart rate / low energy output)
very shorts amount in Z4 and higher (high heart rate / big energy output/need carbohydrates)
80% in Z2.

So that way I can be a type 1 on low carbs but be able to do endurance events and control my blood glucose.

The key is to compete the events with the same thinking keep yourself in Z2 as you do not want to start eating into those carbohydrates you will need for a big hill climb or sprint finish. I personally like to eat little but often on the bike and proper food.

Hope that helps answer a bit.