Intermittent fasting: No advantage over conventional weight loss diets

Feasting eight hours and then fasting the following 16 hours? Or is it even better to fast two whole days a week and then enjoy eating without regrets for the rest of the week? Intermittent fasting, also known as 16:8 diet or 5:2 diet, is trendy. Numerous popular self-help books on this topic promise weight loss without yo-yo effect as well as sustained changes in metabolism and resulting health benefits. The German Nutrition Society (DGE), on the other hand, warns that intermittent fasting is not suitable for long-term weight regulation. In addition, according to DGE, there is not enough scientific evidence on the long-term effects of this dieting method.

"There are in fact only a few smaller studies on intermittent fasting so far, but they have come up with strikingly positive effects for metabolic health," says DKFZ's Ruth Schübel. "This made us curious and we intended to find out whether these effects can also be proven in a larger patient group and over a prolonged period."

In collaboration with a team of DKFZ researchers and scientists from Heidelberg University Hospital, Schübel examined 150 overweight and obese study participants over one year as part of the HELENA study. At the start of the study, they were randomly classified in three groups: One third followed a conventional calorie restriction diet that reduced daily calorie intake by 20 percent. The second group kept to a 5:2 dietary plan that also saved 20 percent of calorie intake over the whole week. The control group followed no specific diet plan but was advised, like all other participants, to eat a well-balanced diet as recommended by DGE. Following the actual dieting phase, the investigators documented the participants' weight and health status for another 38 weeks.

The result may be as surprising as it is sobering for all followers of intermittent fasting. The HELENA researchers found that improvements in health status were the same with both dietary methods. "In participants of both group, body weight and, along with it, visceral fat, or unhealthy belly fat, were lost and extra fat in the liver reduced," Schübel reported.

The changes in body weight distribution in the study participants were exactly determined using special MRT imaging executed by Johanna Nattenmüller at Heidelberg University Hospital. The good news is: a small dieting success is already a big gain for health. Those who reduce their body weight by only five percent, lose about 20 percent of dangerous visceral fat and more than a third of fat in the liver – no matter which dietary method they have used.

The investigators also did not find any difference between the two dieting methods in any other metabolic values that were analyzed or biomarkers and gene activities under investigation.

Although the HELENA study does not confirm the euphoric expectations placed in intermittent fasting, it also shows that this method is not less beneficial than conventional weight loss diets. "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," explained Tilman Kühn, leading scientist of the trial. "But in order to keep the new body weight, people must also permanently switch to a balanced diet following DGE recommendations", he added. According to Kühn, the study results show that it is not primarily the dietary method that matters but that it is more important to decide on a method and then follow through with it. "The same evidence is also suggested in a current study comparing low-carb and low-fat diets, that is, reducing carbohydrates versus reducing fat intake while otherwise having a balanced diet," said Kühn. In this study, participants also achieved comparable results with both methods.

The scientists' credo is therefore: "Just do it!" Body and health will benefit from weight loss in any case, as long as it is achieved by a reliable dieting method and on the basis of a well-balanced diet.

Ruth Schübel, Johanna Nattenmüller, Disorn Sookthai, Tobias Nonnenmacher, Mirja E. Graf, Lena Riedl, Christopher L. Schlett, Oyunbileg von Stackelberg, Theron Johnson, Diana Nabers, Romy Kirsten, Mario Kratz, Hans-Ulrich Kauczor, Cornelia M. Ulrich, Rudolf Kaaks, and Tilman Kühn: Effects of intermittent and continuous calorie restriction on body weight and metabolism over one year: a randomized controlled trial. The American Journal of Clinical Nutrition 2018, DOI: 10.1093/ajcn/nqy196