Researchers added some cinnamon to a bowl of rice pudding and found that blood sugar levels after the meal were lower than they would have been without the cinnamon (see sources below).
Chinese medicine makes extensive use of the Law of 5 elements, a system that describes different kinds of energies and how they affect each other. Among many other things, the law can be applied to flavours and their effect on the body. Every flavour either enhances or diminishes the effect of another flavour.
The effect of sweet food is reduced when the food is combined with something spicy or pungent. This can be a ‘sweet’ spice, such as cinnamon, cardamom, clove or anise; a ‘hot’ spice, such as black pepper or chili pepper; or a pungent vegetable or herb, such as onion, garlic, ginger, chives, parsley, basil, cilantro, mustard, etc.
This is probably what the researchers rediscovered with the rice pudding experiment. It would be interesting to find out if blood sugar levels can be controlled with other spices and pungent foods as well.