I'm not a diabetic but my doctor sent me a letter stating i should follow a diabetic diet. why should i follow this kind of diet if im not diabetic?

Diet: Probably because you have mildly elevated glucose levels that will respond to diet.

I would suspect that your blood glucose is out of the normal range. Before reaching numbers that make the diagnosis of diabetes (fasting 126, A1C 6.5), is a condition called prediabetes. Glucose levels in this range may not be "diabetic" but they increase risk of damage to your heart, kidneys, eyes, etc. A better way of catching these early issues is to use a two hour after meal glucose check

Your doctor has more information about your blood glucose level and may be glucose intolerance or pre-diabetes. A diabetic diet would be helpful for your health even if you do not have glucose disorder. Wish you good health!