(This is the closes category I could find in the forums, but I'm not diabetic).

I've been on (practically) zero-carbs for about 9 weeks now. I have a glucose meter because I occasionally measured by BGL after meals, and I haven't seen spikes.

Due to my natural curiosity, I checked my fasting glucose level this morning and it was 66 mg/dl. The meter warned that this is low. However, I had just finished my morning bike rid (45min) and was feeling fine.

So I wonder if the ketogenic diet messes with how the Bayer glucose strips are calibrated, or if Glucose Blood Level still means anything when one is in ketosis.

Thanks.

Ketosis doesn't mess with the strips, your Bg is likely that low if doing zero carb and a bike ride and I assume an overnight fast. Energy is being provided by the ketones so BG can be low with no side effects.
Low BG and High Ketones is the goal for people wanting a therapuetic level of ketosis.... a 1:1 ratio per Dr Seyfried. Your 66 is about 3.6 in mmlol/L and your ketones may be that high as well. As long as you feel fine, shouldn't worry, though probably should eat if you haven't already

I've heard glucose meters get pretty unreliable at the lower end of the scale.