My younger brother was diagnosed with Diabetes at Age 19, and at that times he weighed maybe 150 pounds. In most cases, Family History has more to do with it than diet or weight, although excessive behaviors of any kind have consequences. My Maternal Grand mother died from High Sugar, her son (my Uncle) died in his 30's due to Low Sugar / Alcoholic Behavior, my Dad wore down and eventually died of complications from thirty year struggle of Infantile Diabetes (High and Low), and my brother, now in his 50's, still takes two small shots of Insulin daily. I've seen and heard about "Sugar" all of my Life.
Fruits are 'Nature's Candy', they contain a natural form of 'sweet' that is more easily broken down and digested. Dairy contains some to (you can thank the cow) but is still within reasonable limits for most. Some Vegetables contain high Starch/ Glucose (Corn, for example) but again it is a reasonable amount.
Processed Sugars, like Candy, Sodas, Sugar Granules, etc., are more concentrated to provide a desired taste. By substituting Equal for Sugar and non-Dairy creamers (I like the sugar-free French vanilla) in my coffee, drinking water instead of sweet tea, eating fruit instead of candy bars/ chips, and avoiding ANY white breads or dairy products, I can lower the sugar intake well within reasonable limits. This allows my digestive system the opportunity to stop 'Storing' and start burning. Again, it is a simple process that even the Military uses in Boot Camp to lean out the bodies of recruits.