The sugar in chocolate is usually table sugar, which isn't as bad as the high fructose corn syrup that sweetens almost everything else in our grocery stores. And the fat in chocolate does not seem to increase cholesterol levels. There is caffeine in chocolate, but only about 10 milligrams per average 1.65-ounce bar, compared to about 80 mg in a cup of coffee. I wouldn't worry about this amount keeping you up all night. But there is a chemically related compound called theobromine as well, and this may enhance the caffeine effect.
Hormonal fluctuations can change a woman's brain chemistry, fat stores, and appetite.
She may crave sweet, high-fat foods at this time, so chocolate is a perfect choice. In addition, chocolate is very high in magnesium, which has been shown to help with premenstrual symptoms. Experience teaches her that it's a perfect PMS food. Well, it's not quite a health food, but it may be better for you than many other vices. A major one, called catechin, may help protect you from cardiovascular disease and cancer.