What is intermittent fasting, and should I be doing it?
What if you could eat whatever you wanted … and still lose weight? Or, what if you only had to count calories two to four days per week and could still lose weight, improve your health, and possibly live longer? Sounds too good to be true, doesn’t it? These are some of the promises of various intermittent fasting–style diets, and they can be compelling. But do the health benefits outweigh the difficulties of this dietary regimen?
Intermittent fasting has long been studied in rats and other animals with positive results on health-related biomarkers and longevity. Recently this idea has caught on as a possible weight and health management tactic in humans. At its core, intermittent fasting is eating few to no calories for a period of time between “normal” days of eating.
There have been many different takes on the concept. There is the 5:2 fast diet™, where you eat a “normal” diet five days per week and restrict calories to 25 percent of your daily needs two days per week, or the Eat Stop Eat version, where you alternate between eating what you’d like and fasting for 24 hours. The 8-hour diet allows you eat whatever you want during a chosen eight-hour period and fast for the other 16. Several other variations of this exist but follow the same premise. Each program defines “normal” differently — some have more strict rules about types of foods and amounts, while others allow free rein.
As with any diet du jour, celebrity hype has drawn attention to intermittent fasting. But, beyond celebrities with personal chefs, personal trainers, and motivation from being in the spotlight, does it really work? Preliminary research suggests some short-term positive benefits for those who can fight through the hunger and maintain compliance. One study suggests that the 5:2 diet plan leads to similar weight loss benefits as a reduced calorie diet (eating, for example, 500 fewer calories than the recommended daily allowance of 1,800-2,000 calories for women and men, along with some positive metabolic changes such as reduced inflammation and improved cholesterol. However, we don’t know if those improvements are due to the weight loss or the act of fasting. Other studies have shown similar short-term improvements in markers of inflammation, which is tied to chronic diseases like cardiovascular disease and diabetes.
The majority of the studies on intermittent fasting in humans have been conducted in controlled environments (i.e. all meals provided and supervised) and for short periods (weeks to a few months). So, we don’t know the long-term effects (positive or negative) of such a diet, or whether or not it’s really a sustainable way of living. While it may lead to health improvements and weight loss, intermittent fasting doesn’t appear to be any better than consistent calorie restriction, which has also been tied to living longer.
Before you start skipping meals or restricting the hours in which you eat, think about how it will affect your quality of life — a topic that is often ignored in discussions about intermittent fasting. Work productivity and physical and mental energy levels are likely to decline during fasting periods. Such a diet regimen can affect social experiences as well (if you can’t eat after 5:30 pm, how will you enjoy a dinner out with friends or family?), which can lead to added stress and reduced quality of life. Mood swings, a.k.a. becoming “hangry,” along with lack of concentration are side effects of long periods between meals and very low calorie diets. Even Jimmy Kimmel, a proponent of the 5:2 diet™ (he’s been on it for about two years now), admitted in an interview that he is pretty unpleasant to be around on his fasting days.
Like other fad diets, intermittent fasting may work for some in the short term, but it is unlikely to be a sustainable way of eating and living. It isn’t as trendy, but eating a well-balanced diet full of plant foods, exercising regularly, managing stress, and sleeping well is your best bet for long-term weight management and overall health.
At Bon Appétit, we know there’s a lot on your plate that you worry about. That’s why we have a team of registered dietitian nutritionists ready to answer your nutrition questions about which food choices will help you avoid unwanted pounds, work or study (and sleep!) better, and form long-lasting healthy eating habits. Email your questions and feedback to [email protected]