Blood sugar levels are not regulated by eating!
If you don't eat for 12 hours, blood sugar levels should remain in the normal range of 70 mg/dl to 110 mg/dl.
Blood sugar levels are regulated by insulin and glucagon. Blood sugar levels rise - the body produces insulin and blood sugar levels fall, blood sugar levels fall - the body produces glucagon and blood sugar levels rise.
If you eat the night before, blood sugar levels the following day should remain in the normal band and hypoglycaemia (low blood sugar) should not be a problem.
What CAN be a problem for some people is a feeling of fatigue mid morning WHEN they have eaten breakfast. This is due to a transitory hypoglycaemia when the insulin production produces a low blood sugar effect before switching off . This mid morning fatigue can be avoided by changing one's eating habits to either avoid, or substantially reduce, breakfast.
The old adage of breakfast is the most important meal of the day is an old wive's tale.
I suggest that a more important reason for one not to fly during Ramadan is that one cannot drink in the fasting period. Dehydration can have a devastating effect on mental ability.