In this study, sixty overweight and obese participants were divided into two groups. One group followed a very-low-calorie diet of 500 kilocalories per day over the course of five weeks. The other group followed a low-calorie diet of 1250 kilocalories per day over the course of twelve weeks. The participants in both groups lost an average of eight to nine kilos, which is roughly 10% of their body weight. All dietary advice was stopped after their diets ended. The participants were asked to return nine months later for a weigh-in. Both groups gained the same amount of weight: approximately 50% of the weight they lost during the diet. The five-week crash diet did not lead to more weight gain than the slower twelve-week diet. 'A yo-yo effect is not more likely after a crash diet than a more gradual diet,' says PhD candidate and researcher Roel Vink.

Two factors did influence post-diet weight gain: the amount of exercise after the diet and the amount of lean body mass lost during the diet. 'We think it involves a loss of muscle mass because the diets are low in calories and protein,' says Vink. “Participants who lost more muscle mass during the diet and those with a lower level of physical activity after the diet gained more weight. These factors likely lower energy metabolism, which could lead to weight gain when you resume a ‘normal’ diet,” according to the researchers. Additional research is being carried out to determine whether crash dieting can lead to other adverse effects and which factors contribute to weight gain after dieting.