It also might be easier to tolerate if you do a ketogenic (very high fat, moderate protein, very low carb) diet for a week or two before. That way you transition to burning exclusively fat, but you can still eat.<p>The not eating thing is actually pretty tolerable if you are already ketotic. But the transition to ketosis can be rough, and it&#x27;s easier if you can eat while that happens.<p>One of the biggest things when you fast or do a ketogenic diet, you lose a lot of water (and with it, salt!), so maintaining electrolyte balance is huge. Your blood pressure  will go down, and you&#x27;ll feel awful if you don&#x27;t add in some salt.