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Impact of fasting interval on blood sugar level

I do 18/6 to 20/4 intermittent fasting on a near daily basis. Occasionally, I can tend to overload on carbs/sugar in that feeding window. I had to get a “fasting” blood test done 8am yesterday. This was 8 hours after my feeding window. I had quite a heavy dinner/supper/dessert on Sunday night (more than usual) and then my glucose came back at 6.6 mmol/L.

Today afternoon I got a call saying I had suspected diabetics. They asked to get a HBA1C test. But I wanted to know my result immediately, so I went to get a blood sugar level reading using the glucose strip, the reading was 5.1 mmol/L today.

The difference?

  1. I had a “normal” eating window last night, as opposed to a “heavier/sweeter” than usual window on Sunday night
  2. And this time, I had fasted around 18 hours since my last food intake as opposed to 8 hours or so yesterday.

Any cause for concern? Did I “overfast” for that second 5.1mmol/L reading? Can what I ate the previous night have such a drastic impact on the glucose reading?

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Answer

The reason your doc wants to see your A1c is to get a better sense for your blood sugar levels over the past 2 months or so. The body should be able to clear a sugary meal in 8 hours, so it really shouldn’t matter if you had a sugar-rich meal the night before. But other factors can influence blood sugar levels — like stress, caffeine — so you might get some variations in glucose readings from day to day.

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