These days new diet fads come along roughly as often as MTR trains during rush hour, so it's no surprise that the latest to grip the popular imagination is actually a reboot of a couple of existing ideas, a kind of a diet mash-up. Intermittent fasting, as the name suggests, combines elements of fasting - not eating for prolonged periods - with elements of the Paleolithic diet, which emphasises eating like our ancestors before the development of settled agriculture about 10,000 years ago, consuming foods such as meat, fish, fruits and vegetables.
The Paleolithic diet is an attempt to eat the foods our digestive systems are best adapted to consume. Intermittent fasting has a similar aim: to mimic pre-agricultural eating patterns, when food was not so regularly available, by not eating on particular days or for a certain period each day. That runs contrary to a lot of recent nutritional wisdom, which tends to favour eating little and often.
"We encourage small, frequent meals as some studies have showed that they might increase metabolic rate," says Sylvia Lam See-way, chairwoman of the Hong Kong Dietitians Association. "[Frequent meals] can keep you satiated so that you can reduce the chance of overeating. And they can stabilise blood sugar, preventing big fluctuations in insulin secretion, which [could] reduce the risk of diabetes and obesity."
Intermittent fasting proponent Robb Wolf, in contrast, says that our eating patterns are those of herbivores, rather than the omnivores we're designed to be. Wolf is a nutritional expert and author of The Paleo Solution: The Original Human Diet. He says that your diet is as much a matter of when you eat as what you eat.
Wolf claims that "for almost every disease under the sun, systematic inflammation is a factor. And every time you eat, there is an inflammatory response. We're constantly bombarding our digestive tract with food, and we need to give it a regular rest."
Fans of the diet claim it can do everything from regulating blood glucose and controlling blood lipids to improving cardiovascular function and reducing blood pressure and the risk of cancer.
But sceptics say there are risks. "Potential dangers from fasting include an increased chance of eating disorders, inadequate intake of micro- and macronutrients, and the possibility of overeating after a fast," says Lam, who doesn't recommend any form of fasting as a diet. "Some acute symptoms [also include] weakness, dizziness, low blood sugar and agitation."