In August 2012, Horizon, a popular BBC broadcast, released a documentary entitled “Eat, Fast, and Live Longer” lauding a revolutionary new diet plan. Since then, I’ve heard a lot about this diet, known popularly as the 5:2 diet. 5:2 uses the idea of intermittent fasting (IF) – where dieters eat normally for 5 days and severely restrict their caloric intake for the other 2 – to help dieters lose weight. Its supporters claim that the 5:2 diet has other large health benefits including helping dieters live longer, protecting them from cognitive decline, and protecting them from cancer and cardiovascular disease. The question is, should these claims be trusted?
They are incredible benefits and we should definitely all be thrilled if they’re actually the case! The only problem is, we don’t really know whether or not these claims are true. Despite the popularity of the 5:2 diet, the body of evidence supporting it is still extremely small and a great deal remains unknown. Much of the diet seems rather arbitrary. For instance, there is no real evidence to support the 5:2 pattern as opposed to alternate-day fasting or other fasting patterns. Likewise, there is little evidence to support the diet recommended 500 and 600 calorie consumption for women and men on their fasting days. The numbers could just as well have been pulled out of a hat for all we know.
Another far more concerning issue is the lack of knowledge concerning possible side-effects of the diet. I ran a brief search of the EBSCOhost database of scientific journals for research that has been published on the IF diet. Of the studies that have been done, the majority used animals models, not human. Of the ones that did use human participants, none ran longer than 3 months or tried to identify potential negative side-effects of the diet.
A third issue you need to be aware of regarding IF diets is that, while animal studies are an accepted form of research, they never generalize perfectly to human beings. Similarly, because researchers control so many different variables in their studies, results obtained in the lab seldom match those seen in real life. That’s why the scientific community runs as many studies as they usually do, trying to get more and more information about the same topic under many different conditions. Unfortunately, as IF diets have only a handful of scientific studies to support them, for now it remains impossible to really say anything for sure about the diet.
On a more practical level, before trying any diet, you also need to consider how it’s going to affect your quality of life. In the long-run, the only diets that actually help you lose weight and keep it off are the diets you can stick to. You need to ask yourself if you would be able to keep to the calorie restriction guidelines the IF diets require. Can you tell yourself no even when you’re very hungry? If you fast during the work days, will you have the energy to do what you need to get done? If you fast on the weekend, will you still be able to do the things you love without falling to the temptation to eat?
The goal of losing weight should always be to improve our quality of life. If true, the claims of intermittent fasting and the 5:2 diet definitely do just that. But its important in critical areas such as your health to keep a healthy level of skepticism – and for now IF just doesn’t have enough evidence to make me comfortable supporting it. If you’re still interested in the 5:2 diet, make sure to first talk with your doctor about whether or not a diet this extreme is right for you or if a diet we know more about would be better.
Asking the question is absolutely worth your time if it helps you avoid a landmine later on down the road.