I love intermittent fasting - it has amazing health benefits including boosted autophagy and cellular repair, reduces insulin resistance, increases the blood levels of human growth hormone and can alter gene expression to protect against disease. BUT THAT BEING SAID - I have an issue with people viewing it as a magic tool for weight loss. Here’s why.
Most of the research on intermittent fasting involves eating in a caloric deficit. For example, a study by Klempel et al (2012) observed the benefits of intermittent fasting in obese women in a clinical trial. The women did lose weight, but they also restricted their calories. This makes it impossible to isolate intermittent fasting as the root cause of the weight loss.
When studies have observed weight loss associated with intermittent fasting, it is often impossible to isolate this factor for a number of reasons. Firstly, when participants are observed they are likely to consume less due to observational bias as explored in a Hammer et al (2009) study and secondly, adjusting an individual’s meal times may also result in a reduced appetite, as shown in a 1998 study.
Ultimately, any research that shows individuals were able to lose weight by adjusting their meal timings is fallible. The participants in every example lose weight because they are decreasing their total caloric intake. It’s more or less impossible to isolate the benefit of intermittent fasting itself, without the confounding variables.
The research that does account for caloric restriction finds no benefit in altering meal timings (like in IF) for weight loss. For example, a four month long study that observed the difference in consuming breakfast or skipping breakfast, controlling for total caloric intake, found no weight difference between groups at the end of the study. Similarly, a randomized controlled trial tested intermittent fasting versus daily caloric restriction and found that both groups lost the same amount of weight.