In certain areas of France, people consume nothing but grape juice during the grape harvest season. These people have been known to have a lower incidence of the diseases mentioned before. However grape juice is not a simplistic liquid, it needs more saliva and digestive juices to make its passage through the human digestion easier, or it can cause cramps.
Besides the obvious good effects, grapes are found to be extremely high in potassium, encouraging an alkaline blood balance and stimulating the heart and kidney processes. They also contain chemicals that help to detoxify and cleanse the system.
So eat up and enjoy!