Many people have asked us about intermittent fasting—our FAQ (11) on the subject is the longest and most detailed on this website.
The most down-to-earth criticism is that intermittent fasting is not sustainable. Diets that focus on denial tend to backfire—you often end up eating more than you would otherwise.
What has been lacking is a well-done study testing the weight control and health benefits of intermittent fasting.
Researchers from Germany have answered the call.
Their randomized controlled trial, published November 23, 2018, in the American Journal of Clinical Nutrition, found little difference between an intermittent calorie-restricted diet and a continuous calorie-restricted diet.
Sixteen researchers from the German Cancer Center and Heidelberg University Hospital followed 150 overweight or obese men and women aged 35-65 for 50 weeks. Participants were randomly divided into three groups: intermittent calorie restricted (five days of calorie-neutral intake and two non-consecutive days of 75 percent calorie restriction), continuous calorie restriction of 20 percent, and a control group with no restrictions. Daily calorie reduction for both intervention groups averaged ~20 percent.
Participants spent 12 weeks in an intervention phase, 12 weeks in a maintenance phase, and 26 weeks in a follow-up phase.
Participant’s weight and health status was monitored for the 38 weeks following the dieting phases.
While recognizing that the results are “sobering” for followers of intermittent fasting, lead researcher Ruth Schubel pointed out in a press release that results were essentially the same in both groups. “In participants of both groups, body weight and, along with it, visceral fat, or unhealthy belly fat, were lost and extra fat in the liver reduced,” she explained.
Although the study does not confirm the “euphoric” expectations, it shows that intermittent fasting is not less beneficial than conventional methods. “In addition, for some people it seems to be easier to be very disciplined on two days instead of counting calories and limiting food every day,” lead scientist Timan Kuhn explained. “But in order to keep the new body weight, people must also permanently switch to a balanced diet following Cancer Research Center recommendations,” he added.
“Our results on the effects of the ‘5:2 diet’ indicate that intermittent calorie restriction may be equivalent but not superior to continuous calories restriction for weight reduction and prevention of metabolic diseases,” the researchers concluded.
Intermittent fasting works—if you actually do it.
Digging deeper into the details suggests that the results were not as rosy as the press release suggests.
Compliance was very good during the first 12 weeks when dieters were receiving biweekly calls from dieticians. However, at week 24 only a third of participants reported doing the two days of restriction. By the end of the 50 weeks, only about one in five participants were still fasting twice a week. Not surprisingly, the intermittent fasting group regained the most weight as the study progressed.
If intermittent fasting appeals to you, give it a try. But don't expect benefits that can't be achieved eating regular meals of quality foods--and regular exercise. Sustainability is the key. No diet or exercise regimen will work if you can't stick to it. Don't defeat yourself by making it harder than it needs to be. Find a plan that you enjoy and are comfortable doing as far as you can see, hopefully for life.
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