I have been fasting intermittently and regularly for 24-72 hours with excellent results.
I ride 3-4 times a week for 2 hours in zone 2. Lately after reading and Youtube vids on endurance training - on ride days I don't fast as I use about 30g of carbs for the second hour.
Longer-term fasting has really good benefits for health. I follow dr. Mindy Pelz and its been instrumental for inflammation and general health. I fast 24 hours once a week and 48-72 hours once a month.
I highly recommend everyone to try it.
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If you have a steady supply of something, you can afford it and it's not interfering with your life, there's nothing wrong with being addicted. - Roland Griffiths