I think you know the answer to the question if white sugar is bad for you. White sugar comes from sugar cane, which is a plant, so why is it so bad for us? Can you say highly processed? Yeah, the gorgeous white crystals most people pour into their coffee every morning has zero nutritional value because it's all stripped away. White sugar is a refined sweetener, adding nothing but calories and taste to foods.
When you eat foods with refined sugar like sodas, candy bars, or high carb meals, it upsets the body's blood sugar balance. This triggers the release of insulin, which the body uses to maintain blood sugar levels at a constant and safe level. After insulin levels spike up, they quickly crash soon after, leaving you feeling sleepy, and possibly even hungry again. This often leads to more snacking and usually on sweet or refined carb treats. This cycle leads to overeating, since you are not really hungry, and weight gain. This is the reason carbs are often viewed as “bad” nowadays, and why the Atkins Diet is so popular.
Refined carbs such as white bread, white pasta, white rice, baked goods such as cookies have the same effect on your body, so that's why you should look for alternative foods made from whole grains. When you feel like snacking, stick to straight up fruits, nuts and ones that contain whole grains. These are slow burning carbs that contain vitamins and fiber too, so they'll give you a consistent flow of energy without the sugar meltdown.