Intermittent fasting is all over the place. People who are doing intermittent fasting often freely share their experiences--on social media, at parties, and at work. What is the allure of intermittent fasting, does it work, and do I recommend it as a dietitian? These are all great questions, and I will posit my own answers based on the literature and based on my own experience as a registered dietitian working with patients.
What is the Allure of Intermittent Fasting?
Intermittent fasting seems like a great idea. Wherever you look, people are talking about their experience with intermittent fasting. Everyone seems to be losing weight--at least those who talk about it are losing weight! I await the day when people stop looking for the next quick answer for weight loss or the magical solution for obesity. While we don't actually have that quick answer, to the casual observer, intermittent fasting seems to be it. People are always telling their stories of weight loss while doing intermittent fasting. They are eager to recommend it to their family members, coworkers, friends, and social media followers.
For the most part, the people who talk about intermittent fasting are those who had success with it. The people who tried intermittent fasting and either did not lose weight or found it too difficult to stick to aren't as vocal about their experiences, or they get drowned out by the minority who did lose weight.
Does Intermittent Fasting Work?
The quick answer is that it works for those who post about it on social media. Meaning, if it works for someone, they are more likely to talk about their success than if it does not work for them.
But what does the research actually say? There are a number of studies on intermittent fasting, and it is important to understand that all studies on a given topic are not done the same way. Some important characteristics about studies on intermittent fasting are as follows. Many studies do not keep track of the number of calories people ate while they were doing intermittent fasting or while they were eating typically. Those that did keep track of calorie intake found that those in the intermittent fasting group were actually eating fewer calories than those in the group that was not practicing intermittent fasting. The decreased calorie intake likely explains the weight loss in the intermittent fasting group rather than the time of day that they were eating their food. The few studies that actually assigned both groups to eat the same prescribed food did not see a difference in weight loss between the two groups.
From my experience working with patients who have done intermittent fasting, most people report that they lost weight. The question I always ask is why they are coming to see me for weight concerns if intermittent fasting works for them. The usual answer is that it was too hard to stick to. Yes, it will work while patients do it, (because it is lower in calories than their usual eating,) but most people can't do it long term. That is where the problems arise.
There is a well known phenomenon called weight cycling. This is when someone goes on a diet, loses some weight, then inevitably stops the diet and regains weight plus some. This is seen after every type of diet, not just intermittent fasting. Studies seem to show that yo-yo dieting or weight cycling seems to lead to an issue in which a person's metabolic rate declines so that they actually need fewer calories to maintain a given weight compared to what they needed to maintain that weight before yo-yo dieting.
As a Registered Dietitian, Do I Recommend Intermittent Fasting?
Because of the evidence around intermittent fasting and dieting in general, I don't usually recommend intermittent fasting. If someone really wants to try intermittent fasting, I will explain the evidence around it and help the patient eat well while they are trying it. As we work together, we also work on developing a more sustainable mindset around eating, and that can shift how the patient approaches eating in general.