Calories In = Calories Out
What does that mean? It is important to know what you eat. It is important to know how much physical activity you do. The food you eat is "calories in". The physical activity you do is "calories out".
If calories in = calories out, you don't gain or lose weight. You stay in balance. Calories in will be greater than calories out if you eat a lot and do little activity. This leads to weight gain. Weight gain is a risk factor for diabetes. You can stay in a healthy balance if you pay attention to calories in and calories out.