The widespread belief for centuries throughout the grape-growing areas of Europe that grapes, grape juice, and grape products generally have curative properties. It has not been a dominant belief but one of those examples of folklore in the background of all cultures, a cure in the same category as goats milk, honey, and much else. Its advocates might well point to the recent evidence that a moderate intake of wine has beneficial effects on health as validating their belief.
In the early 20th century, Bernarr Macfadden (1868-1955) claimed that a grape diet would cure cancer. The publisher of a number of health magazines and author of the massive five-volume Encyclopedia of Physical Culture: a work of reference, providing complete instructions for the cure of all diseases through physcultopathy (1912), he offered a prize of $10,000 to anyone who could prove that a diet of grapes did not cure the disease. Proving a negative is notoriously difficult, and the prize remains unclaimed to the present.