I've long said sugar is bad. But I haven't said it on this blog yet, so there it is: avoid unnecessary sugar. Avoid it more than you avoid fat, salt, caffeine or alcohol (if you avoid these at all).
The reason is simple: it provides little in nutrients and wrecks havoc with your insulin.
A new research came out recently -- which does not surprise me a bit -- that some cancer cells feed on glucose and fructose, two types of sugar present in many foods, from cookies to sodas and anything else that contains corn syrup.
The MSNBC article covering the UCLA study reports:
"Tumor cells fed both glucose and fructose used the two sugars in two different ways [...] Tumor cells thrive on sugar but they used the fructose to proliferate."
For better alternatives to sugar (if you must have it), try Stevia leaves or Agave nectar. Both are low on the glycemic index, hence they are a little healthier than pure sugar.