Like the keto diet, fasting for one or two weeks may not accelerate weight loss and could actually slow the loss of body fat. While fasting can lead to dramatic and consistent weight loss, some research groups have reported “extremely disappointing long-term effects” after fasting. In one study, obese subjects gained back all the weight they had lost after fasting, though it’s argued that they may have gained even more if they hadn’t fasted.
However, some research teams have reported better outcomes. In one study with over 100 individuals, 40 percent of the group retained at least 7 pounds of the weight they lost after fasting for 10 days. In a different study, subjects lost an average of 52 pounds after fasting for 44 days, and 40 percent of them retained at least some of that weight loss one to two years later.
Contrary to conventional wisdom, fasting groups in a study were more successful with long-term weight loss compared to groups following the standard low-calorie diet. A study comparing different weight-loss approaches found that subjects who had undergone fasting a few years previously had better long-term weight maintenance compared to those instructed on daily caloric restriction.
In the long term, however, fasting can lead to less fat loss, as the body starts cannibalizing itself and burning more of its own protein for fuel. Additionally, adding exercise during a fast may worsen the loss of lean tissues. In one study, less than half of the weight loss during the first few weeks of fasting came from fat stores. Therefore, even if weight loss is doubled on a fast, it may result in less body fat loss.
Overall, it appears that fasting can lead to rapid weight loss in the short term, but the long-term effects may vary, with some individuals experiencing more sustainable outcomes.
