I think you would need to do a heck of a lot more testing than that.
All sorts of things happen to our blood glucose levels in the mornings. It is called Dawn Phenomenon, plus all the usual factors such as stress levels and activity levels for the morning routine. Then of course food factors in. And portion size. Even coffee, if you are one of the few whose blood glucose is affected.
So you would have to run a huge series of tests, over several weeks, using standardised conditions, such as weighed porridge and milk, exact timing, and carefully controlled activity levels.
My first reaction is - if you drank lemon water, what didn't you drink instead? And have you carefully tracked your usual morning blood glucose levels for weeks and months before this, for comparison?
Sorry - it is not my intention to squelch your idea. I would love it if my bg were controllable by such a beautifully simple solution. But these things have never, so far, worked for me, so I have become rather sceptical. Good luck with the testing though. And I will be interested to hear if the lemon water pans out over time.
