"There is a history in Judeo-Christian societies – and likely in many other religions, hence the widespread practice of fasting – where demonstrating a lack of need for material things, especially food, and being able to demonstrate self-control and discipline are signs of spiritual transcendence," Dr Woolhouse says. Famously, Italian saint Catherine of Siena would fast for prolonged periods of time as a means of demonstrating her devotion to God through extreme self-control. "But there's also a class dimension to this," Dr Woolhouse continues, "because being able to demonstrate a lack of need for material goods, like food, suggests social transcendence too; it's symbolic of living a life whereby our material needs aren't a daily concern." She adds that "fad diets are very unlikely to take off in societies where there are food shortages or food insecurity."