A diabetic should never go all day without eating something unless a doctor has approved the diabetic to do so such as in fasting for a test.
Diabetics should never skip any meals during the day for weight loss or anything else because the blood sugar levels could drop which could become life threatening if they don't seek medical attention right away.
Blood sugar for a diabetic can either go up or down without eating so never skip a meal unless advised by a doctor when you're diabetic.
My mother is a diabetic and she has had to fast before a test but she was advised only to do so before those tests and never without a doctors guidance.