I have battled "low" blood sugar or Hypoglycemia for most of my adult life.
That can turn into diabetes if not controlled through proper diet.
When I shot alot I found that by not eating a big breakfast and only eating
small amounts of healthy protein and fats an hour or so before shooting helped alot. I would eat a chicken thigh or some venison or sometimes nothing at all and never, never ate a big meal between events. If you eat a big meal your blood sugar goes up, and what goes up must come down (sleepy, groggy) or in the case of diabetes what goes up stays up!
Moderate exercise daily, ie, walking briskly, hiking etc..is proven to help stabilize blood sugar. A high protein and a high fat diet also does the same, but it has to be HEALTHY fats...coconut oil, olive oil, healthy animal fats...etc...
I also carried some apple juice with me while shooting in case I got "fuzzy".
After shooting was over I would eat a meal. Drink lots of water and stay hydrated, and eat only good quality protein in small amounts in one or two hour increments to stay "level".
Nuts are good and animal proteins too....carbs?, not so good.....