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5/2 Diet, Back to Back Low Calorie Days?


Quick question. What is the downside of running your two, 800 calorie fast days back to back. Say I happen to train everyday except for Wednesday and Thursday. What’s the problem with fasting on those two days?


I did the 5/2 diet before I started my new job.

I loved it, for the first time in a very long time I felt the difference between eating because I was hungry, bored, or emotional.

The downside? For me the drop in blood sugar made it difficult for me to concentrate. My old job did not require extensive mental work, so I could get around this. My new job, however, requires me to be mentally alert most of the time, so the 5/2 diet was not doable.

Hence, I expect the effects of low calorie and low blood sugar to be more pronounced - worse fatigue, reduced ability to concentrate, zoning out, etc. There may be other effects - I am not a dietician so I don’t know.


800 calories is LOW, really low, they’re not meant to be back to back otherwise they’d probably be higher calorie. They’re meant to provide two dips spread out throughout the week. Putting them together, vs spreading them out more evenly, will not provide the same benefits of the diet in the long run, and two 800 calorie days in a row could start risking some LBM loss. Although minimal, I’d never do anything that would risk losing the precious muscle you work so hard for.