hi welcome, if you are newly diagnosed then you may well see big swings (I know I did) took me a month or 2 of eating a better diet to settle down, but yes in deed your diet is all important, what you eat is what makes all the difference please go ahead and read some of the post regarding diet on this forum, carbohydrate intake is very important so please read about that too, good luck
edit, there is a crazy amount to learn so please go ahead and ask any questions you may have, and to answer the question you asked, I believe we should be hoping for readings of 4.4 before eating to 7.8 two hours after eating, I assume your testing your blood to know your readings