Capsaicin is the compound in chili peppers that makes them flavorful. It has been shown not only to add a delicious burn to food, but also to reduce fatigue in mice. In humans, consuming 2.5 mg of capsaicin per meal (7.68 mg / day) has been shown to restore energy balance in the body.
Capsaicin affects energy because it affects glucose metabolism in the body. When capsaicin gets into the intestines, it triggers a vagal response to the brain, regulating appetite by helping hormones from the brain's appetite regulating center to more effectively detect when enough is enough.
The amount of capsaicin varies widely between different types of pepper and is proportional to how hot the chili tastes. For example a mild jalapeño: 0.165 to 0.33 mg of capsaicin; Serrano Chilli: 0.396 to 1.518 mg of capsaicin. Spicier chilies like a bird's eye view of Thai chilies and habaneros can be an efficient way to get capsaicin (if you can handle it).
Instead of trying to add up capsaicin levels, just try adding spicier foods to your diet. Use extra cayenne pepper when cooking. If you order Thai, Indian or other spicy foods, order them one level hotter than usual.
Remember, it's not just the generic "spiciness" that matters, but the capsaicin itself. In other words, spicy foods that get their burn from non-capsaicin compounds like mustard, horseradish, black pepper, and ginger work does not affect the energy balance in the same way.