In the morning I ate healthy breakfast of as brown rice and miso soup along with some vegetables.
For lunch I had a bowl of corn flake cereal and mixed nuts.

One hour after lunch, I started suffering from a severe headache.
I checked my glucose level. It was surprisingly high; it was 277.
In order to lower my blood sugar level, I walked for 15 minutes on the treadmill and did a 10-minutes muscle training.
By the time when finished the short exercise, my headache was gone.
I checked my glucose level again. It was lowered to 94.
So, I guess either a corn flake cereal or mixed nuts is not good for my body.
***
PS: After I received the result of an allergy test on June 3rd, I learned I am allergic to a corn flake cereal and a cashew nut. I started avoiding consuming these foods since then. My small mystery was solved.
♬ Any feedback? (^^♪
