Human beings, whether we like to admit it or not, are not that far removed from early mankind, that is, we are not that far evolved from the first evolved humans. Humans were generally gatherers. The early humans ate what was available to them, when able to find edible foods. What was available to humans was very natural, totally unprocessed food stuffs, complex carbohydrates, proteins, natural sugars....these were available to the early humans. The human body then and now is very good at breaking down and using any kind of carbohydrate.
In the past 100 years or so, much of our food is highly processed for many reasons. Cost, mass production, maintaining freshness, packaging, enhanced taste are many of the goals of processing. The processing of the food means that our barely evolved digestive system that is used to processing complex foods are now seeing and processing less complex foods, especially carbohydrates.
One thing that needs to be known is that sugars are carbohydrates that the human body will break down during digestion and store them in the body. This leads to quick weight gain. That being said, sugars in fruits are more complex and are not as easily processed and some do not trigger glycemic processing in the human body. Again, the less processed, the less bad it is for you in the case of sugars.
Bottom line: To maintain weight avoid sugars if possible. The simpler sugars should be avoided at all costs, no alcohol, no simple sugars.