Sugar

Sugar is the generic named used to describe sweet-tasting compounds.
Sugar is both found in refined and processed forms (white sugar, cane sugar), and in various whole foods such as fruits.

Sugar and its different forms

The simple sugar forms are glucose, fructose and galactose. They're also called monosaccharides, because they're the most basic forms of sugar and cannot be further simplified.

Sucrose (white sugar), lactose (found in dairy milk), and maltose (found in grains) are disaccharides, because they're composed of two monosaccharides each--glucose + fructose, glucose + galactose, and glucose + glucose, respectively.

Weight gain

Refined sugars are very calorie dense, while offering no nutrients whatsoever. Similarly to oil, it's very easy to eat significant quantities of it and to not feel full because you didn't get any nutrients. Or if you feel full at the end of the day after eating lots of sugar, you'll have had less calories dedicated to nutrients, and more calories spent uselessly in empty calories (sugar), which will mean you're more likely to not meet the nutritional daily requirements.

Refined sugars are significantly higher in calorie density, since all nutrients have been removed and only the calories of the sugar themselves are left.

Sugars with no nutrients:

• 1 cup corn syrup: 965 kcal
• 1 cup white sugar: 774 kcal
• 1 cup brown sugar (unpacked): 551 kcal

Sugars with nutrients:

• 1 cup date sugar (dried and pulverized, whole foods): 415 kcal with fibers, some vitamins and some minerals
• 1 cup maple syrup: 819 kcal with lots of vitamin B2 and manganese, and a bit of other minerals
• 1 cup blackstrap molasses: 960 kcal with optimal amounts of almost all minerals and vitamin B6, and some other vitamins