3 hours ago, UbonThani said:

4 weeks is for proper fat adaption as the major source without headaches and loss of energy. Start of keto is 2 to 4 days however. A serious keto runner would prepare months in advance however with diet planned out.

 

If you just want to lose weight then the weight will start dropping off after day 4 or 5 on a keto diet. The first 4 days loss will mainly be water loss.

 

 

Keto is like a key that unlocks the body's ability to utilize fat stores as energy.  As long as carbs are the main fuel source and you consume them throughout the day, your insulin levels will always be too high to allow the body to access fat stores; all that will be possible is to store fat, not burn it.  That is a fact.  Cut the carbs and Keto will kick in as soon as glycogen stores become depleted, and when keto bodies began to populate, you will begin to burn stored fat as fuel.  Simply really.  

HIT depletes glycogen in 90 mins to 2 hours also. Problem is HIT shortens your life and people with bad joints can't do it anyway.

On 2/7/2020 at 12:34 PM, WaveHunter said:

That is a little misleading.  For athletes who are interested in ketosis, it is because they want to become more "fat-adapted".  That means they want to alter their metabolism to burn fat as a primary fuel more effectively, and be less reliant on carbohydrates in order to avoid "bonking" without the need for sports gels or snacks while competing. 

 

THAT can takes weeks for the body to become fully adapted, but ketosis becomes highly beneficial as soon as glycogen is exhausted and in response to that, ketones bodies are providing sufficient fuel for the brain, and fatty acids are being mobilized due to lowered insulin response resulting from lowered carb intake.

 

The key is limitation of carbs.  If carbs are being consumed above around 50 grams a day, insulin response will be to high to allow ketosis to happen.

 

Ketosis indeed happens in as little as 48 hours if water-fasting, and 3-5 days if carbs are limited to around 50 grams per day.

Agreed with all that but if you equate 'fat burning' with 'ketosis' I differ. I don't think anyone will be efficiently fat burning throughout a marathon or even half marathon after only a few days, as can be witnessed by many questions from athletes on Reddit or Facebook pages.