What is intermittent fasting?
The evidence behind a popular eating trend.
Intermittent fasting is a pattern of eating that has continued to gain popularity. It consists of severely limiting calories either during certain days of the week or during a certain number of hours during the day, followed by "feast" days or hours during which you eat without limitation. It can be done numerous ways. One example involves eating "normally" five days in the week, and then restricting food intake to around 500 calories during the two fasting days. The claims are greater weight loss, reduced inflammation, and improved heart disease risk factors compared to traditional diets. Let's take a look at the claims and the evidence supporting them.
Greater weight loss. Here's what we know from research: as with most diets, fasting does result in weight loss as long as the dieter eats fewer calories than he or she normally would. Does it result in a greater weight loss? Often times yes. The problem is, the time frame for these diets is short – a few weeks to at most a few months – and for good reason. It is difficult for humans to avoid overeating and consuming too many calories on the "feast" days or hours, after a period of "famine," resulting in overall excessive calorie intake. Blame it on evolution or genetics or our simply just our body's amazing ability to keep us alive no matter the availability of food. And because of this evolutionary mechanism, there's a high potential for weight regain with successive periods of "famine" followed by "feast."
Disease control and prevention. There's conflicting evidence on intermittent fasting and lowering inflammation and improving certain conditions like heart disease and diabetes. In some short-term studies, fasting has been shown to improve blood sugars and improve other disease factors. However, fasting can also be harmful for people with diabetes, causing unstable blood sugars and potentially dangerous hypoglycemic episodes. Additionally, the act of feasting and fasting repetitively can actually increase stress on the body and increase inflammation.
The takeaway. For the average, healthy individual, there aren't any immediate risks to practicing intermittent fasting. However, there's stronger body of evidence supporting a structured and balanced pattern of eating that does not include the feast/famine cycle at all. Ultimately, if you are considering intermittent fasting as a method of weight loss or improving your health in other ways, first consult with your doctor to determine if you have any health conditions that are contraindicated with this way of eating. Then, consult with a registered dietitian who can help you make a plan that ensures you'll get all the nutrients you need and optimize your health.