Fasting has been used for health and religious reasons for hundreds of years and due to an explosion of new interest from the media, intermittent fasting is becoming the newest trend in dieting. But is there any supporting scientific evidence that would make it anything more than another weight-loss fad? Does intermittent fasting work and hold up to their claims?
What is intermittent fasting?
There are three types of intermittent fasting (IF) diets: alternate-day fasting, whole day fasting, and time-restricted feeding. Alternate-day fasting involves alternating between fasting days and days of eating until satisfied. Whole-day fasting involves 1 to 2 days of complete fasting per week and eating until satisfied the other days. Time-restricted feeding involves the same eating routine each day, using a certain number of hours designated as a fasting window and the remaining as the feeding window. Time restricted feeding is becoming the most popular type of IF diet in the health and fitness industry, and often with promises of amazing (albeit unrealistic) results.
Does intermittent fasting work for weight loss?
Currently, one of the most popular reasons for following this kind of diet is for its claimed aid in weight loss. It is important to keep in mind that no diet has ever shown long term success with weight loss (longer than 2 years) but hey, maybe this one is unique, like all the other one-of-a-kind diets out there, right?
According to the current research, intermittent fasting works for weight-loss just as well as any other traditional caloric restriction diets- which is VERY POORLY. In a review of 12 independent studies comparing the effectiveness of intermittent fasting to continuous restricted eating, 9 of the 12 studies concluded no significant differences between the groups. Overall, there is very limited evidence suggesting IF diets to be superior.
It is well documented that the body undergoes adaptive responses (both physical and mental) to calorie restriction that can slow down and reverse weight loss when dieting. For example, these changes include increased appetite, reduced energy expenditure, and hormonal changes that promote the accumulation of fat tissue and the loss of lean muscle tissue. A major reason that IF is believed to be effective is based on the idea that alternating periods of energy balance used in IF could reduce these adaptive responses and therefore increase the efficiency of weight loss. Interesting idea, but what does the research say? Overall, there is no evidence that suggests IF reduces the adaptive effect of decreased energy expenditure from calorie restriction relative to the effects of continuous restriction diets. There are currently 3 studies that directly compare energy expenditure of IF to continuous restriction diets. Overall, they have not shown intermittent fasting protocols reduce the adaptive responses to energy restriction relative to the effects of continuous restriction diets.
Studies have not shown that intermittent fasting reduces the body’s adaptive responses to energy restriction.
Does intermittent fasting work in reducing the risk for illnesses such as heart disease and diabetes?
Some claim that IF diet will help to improve cardiometabolic health and diseases such as diabetes, high blood pressure, insulin resistance and high cholesterol. However, any evidence of improvements is quite lacking. It is important to note that many of the studies looking at changes in risk for cardiometabolic diseases compare low-calorie diets to IF. One meta analysis that conducted this sort of comparison did not show any difference in cardiometabolic health markers such as cholesterol, blood glucose, and A1C levels. Another study, published in JAMA, also found no difference in these health indicators (such as blood pressure, blood glucose, insulin resistance and CRP).
If not intermittent fasting, then what?
There is still a lot of research needed on intermittent fasting to fully understand the potential benefits and risks of this type of diet. For now, the evidence does not justify using this type of method for weight-loss (or any other method or diet for long term weight change) nor for cardiometabolic health. This type of diet is extremely difficult to follow in an everyday setting for any length of time, as all diets are.
Evidence does not justify using this type of method for weight-loss (or any other method or diet for long term weight change) nor for cardiometabolic health.
Non-diet approaches to health and wellness, such as mindful and intuitive Eating, are more effective long term and reduce the chances of developing an unhealthy relationship with food and your body. There are many reasons for this- but perhaps the most compelling is the fact that without an answer for long term weight loss, weight cycling (or yoyoing) occurs in up to 95% of people which leads to poorer physical and mental health. As the authors of this very in-depth article state “Much research suggests damage results from a weight-centered focus, such as weight cycling and stigmatization”.
Does intermittent fasting work for weight loss or improve cardiometabolic health? According to current evidence, no. However, there are answers to our health problems if we allow ourselves to step away from weight loss-centric nutrition advice and focus on actual health.
Co-written with Holly McGarr, BSc Nutritional Sciences, MScPH (candidate)
For more information on better alternatives to intermittent fasting for health and well-being, check out this article about the basics of Mindful Eating or this article with Mindful Eating Exercises to practice.