Sugar can take many forms, high fructose corn syrup, cane sugar, brown sugar, glazes, honey, etc. Too much sugar can cause fluctuations in blood sugar and make you feel tired. Try to have your sugar as a complex carbohydrate such as a whole grain or fruit with fiber. Fiber slows the release of sugar into the blood and stabilizes blood sugars. While sugar itself doesnt lead to diabetes, the overweight from excess calories can lead to insulin resistance and high blood sugars.