There are many foods that contain natural caffeine. In theory there is nothing inherently unhealthy about consuming natural caffeine, though many in the medical community will warn about the risks of excessive consumption. Always use in moderation seems to be the safe bet.
Foods with natural caffeine:
Chocolate: Caffeine is found naturally in cocoa beans, so any real chocolate made from cocoa beans has a little bit of natural caffeine.
Coffee: Coffee beans are some of the most popular sources of natural caffeine. The actual caffeine content can vary depending on bean type and even “decaffeinated” coffee still contain trace amounts of caffeine.
Tea: Black tea, or any tea that has been oxidized and dried, typically has the highest caffeine content.
The kola nut: The nut, which grows as a fruit of the evergreen kola tree, is often chewed raw. It can also be brewed into a drink much as coffee would be.
Yerba mate and Guarana plants: Both contain natural caffeine, there leaves can be used to make an infusion that resembles green tea, the caffeine content tend to be much stronger than regular tea.
Always check with your doctor before beginning any new diet or exercise regimen to make sure you are medically able to participate. Only your doctor can determine how much exercise is safe for you. Starting an exercise program that is more strenuous than you are ready for can result in injury and serious medical problems.