Generally speaking, sugar in fruit is not bad for us. As a matter of fact, fruit contains a natural sugar, fructose, that is better for you if you're diabetic. Due to the slower digestion, fructose doesn't cause the exact high glycemic swings as other types of sugars. In 2008, the American Journal of Clinical Nutrition advised diabetics to utilize fructose rather than sucrose based on research studies.
Few fruits contain enough sugar to make them bad for you.
However, you do have to watch which fructose you are becoming. There is natural fructose and high-fructose corn syrup. The latter is not natural and will cause your blood sugar to spike. This is something you also have to watch out for when buying canned fruit. Much of it is packed in that high-fructose corn syrup. If it doesn't say packed in natural juices, then purchase your fruit either fresh or frozen instead.
You still need to keep track of how much sugar you are consuming, even if it's largely fructose containing fruits. The American Heart Association recommends up to 24 g of sugar each day for females and 36 grams for men. But you can easily exceed that if you do not make the perfect selections. For instance, two cups of sliced bananas has 36 grams of sugar by itself. If you add in the sugar you are getting from the rest of your food, you are most likely far in excess of what you should be eating each day.
Obviously, as we have known since elementary school, it can cause tooth decay. But it also causes weight gain and increases the triglycerides in your blood stream. That's been shown to increase your risk for high cholesterol, heart disease and stroke.
Strawberries, bananas, oranges, kiwi... the healthy list continues on and on. Fruit is touted as a super-healthy snack option, but while the fiber and other nutrients found in fruit are a great part of a diet, many varieties can also be very high in sugar. Too much sugar, regardless of where it comes from, can have some serious unwanted effects. (Yes, even sugar from fruit if you consume a lot of it!) Does this mean you are not even safe in the produce aisle? Well, you are definitely safer. But it may be smart to restrict your fruit-based sugar consumption.