Just to say, coming from the biochemist, the phrase “sugar is just sugar” isn’t really true. There are many, many different forms of sugar (glucose, sucrose, fructose, maltose, ribose, galactose, etc etc etc.), each of which plays a different role in our body, and is metabolized differently. The research suggests that fruit tends to have a higher percentage of complex sugars that are digested slower and are used for more purposes in our body (and sugar is used for a huge number of things beyond energy, such as building blocks in some proteins). Sugar from highly manufactured sources, especially soda, tends to be less complex, metabolized quickly, increases our Blood-sugar levels easier (leading to diabetes) and more quickly converted to fat stores (contributing to obesity).
Now, I can’t say with certainty that this is precisely true, as the links between those sugars and metabolism isn’t the best understood at the moment. Metabolism is fiendishly complex. However, it is completely true that different sugars are metabolized and used differently, so sugar is not just sugar. However, you can make arguments that fructose, say, isn’t so bad. But that i can’t be sure of. I just know the research does suggest a causual link to complex sugars being better for you, and manufactured sugars being worse.
Now, that doesn’t mean that if you diet was only sugary fruits you would be okay. If you eat too much of any sugar you won’t be that good. But eating complex sugars, in moderation, is most likely much better for you (and to a degree necessary), while other sugars have less use in the body.
@Taciturnu also, you’d be surprised how correct that phrase is. Each sugar molecule is recognized by different proteins in the body, and so it doesn’t say “oh, this is from fruit!” But it does say “oh, this is sucrose” or “oh, this is galactose. I’m going to release different metabolites accordingly”. And different foods have different levels of these carbohydrates, and so each food will effect different changes in your metabolism.