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EventsDo you recommend going in and out of ketosis?
, medical content by Dr. Jason Fung, MD
in Dr. Jason Fung, Intermittent fasting, Keto, Ketosis, Low carb & high fat, Q&A 
What do I need to know about exercising while doing extended fasting? How much salt should I add to water when I’m fasting? And do you recommend going in and out of ketosis?
It’s time for this week’s Q&A about intermittent fasting and low carb with Dr. Jason Fung:
Exercising while fasting
Is there anything I should bear in mind regarding extended fasting and endurance training? I’m looking at starting some extended fasts of around 36 hours, but I will also be exercising quite heavily as I’m training for a marathon. Any advice would be really appreciated.
Chris
There is a period of adaptation, about 2-3 weeks to get your body used to exercising while fasted.
Dr. Jason Fung
Water fasts and staying hydrated
Hi Dr Fung,
Do you have a recipe for how much salt to add per one liter of water, for a person to drink while on a water fast to maintain hydration and electrolytes? Every person drinks a different amount of water each day so the question is if a person only drank this salted water and no other liquids.
Thanks,
Rachel
There is no single right answer. Some people don’t use salt at all. Others get dizzy if they do not take supplemental salt. The kidneys have an extraordinary ability to retain salt in the the event of sodium depletion. For shorter fasts (24-36 hours), it is likely not necessary to supplement.
Dr. Jason Fung
Going in and out of ketosis regularly?
Is it necessary or recommended that you switch out and into ketosis again on a regular basis? Online I read that some experts advise that, in order to maintain insulin sensitivity. For women I even read about a high-carb “week” during the menstrual cycle, altered with a ketogenic diet in the other 3 weeks. Or 5 days keto, 1 day fast and 1 day feast, with higher carbs.
I watched many videos on the dietdoctor website now (love it!) But have not come across any such advise yet.
Mirjam
I think it is beneficial to switch things up every few weeks, too, although most evidence is anecdotal. There is one small study MATADOR, that suggests this is true. In this study, alternating periods of calorie restriction with normal diets seemed to be better than continuous dieting. The same probably holds true for ketosis.
Dr. Jason Fung
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And ketogenic dieting is NOT a fad. Low-fat diet is a fad, vegetarian diet is a fad, eating 11 servings of grains and massive amounts of sugar and treating a calorie like any other calorie is a fad. They have all failed.
Some of us, myself included have lost lots of fat and been healthier than we have been in years. Personally i dropped 80 pounds, I am off all my HBP meds and my T2D is gone.
So please, spare the advice that everyone that suffers from obesity has heard a million times before. It’s amazingly disrespectful to think that they haven’t tried that old saw before.