The Mayans considered chocolate "The Foods of the Gods" and drank a very bitter mix of it with peppers for royal and ceremonious purposes. The Aztecs held this unsweetened chocolate drink to an elevated status. Europeans did not take to chocolate until sugar was substituted for peppers. Milk was added to chocolate hundreds of years later, creating milk chocolate.
Chocolate contains cocoa butter, which is high in saturated fat. However, 1/3 of that fat is stearic acid which the liver can transform into oleic acid. Oleic acid is the cardioprotective fat found in olive oil. Chocolate also contains magnesium which is a vital nutrient for many areas of the body, including bones, cardiac health, detoxification, enzymatic function and as an anti-spasmodic. The fact that it contains magnesium is one therapy for why some women crave it before their periods. Chocolate also contains phosphorous which is necessary for good bone health. It is a source of phenylethylamine, which is a stimulatory neurotransmitter that makes people feel alert, focused and energized.
Research done in South Koreas has found that cocoa contains more antioxidants than black or green tea or red wine. The key is the higher the cocoa butter the more the chocolate has antioxidants in it. Most commercial candy bars are only 20% cocoa butter, while darker and finer chocolates can contain up to 70%. Chocolate also contains from 10-30mg of caffeine per bar. That is not really that much, for comparison, coffee usually contains over 100mg per cup, while tea contains around 50mg of caffeine.