By Samuel Bullard, graduate nutrition student in the Coordinated Program
In recent years, intermittent fasting has become a hot topic in the health and wellness world. Countless books and blog posts have been written about the benefits and strategies related to the timing of fasting and eating. Traditionally, a fast is when someone does not eat for a period of time. Before it became a health strategy, millions of people around the world fasted for religious purposes. Fasting is not a new idea, but fasting for weight loss and even bodybuilding is a relatively new idea.
There are many different kinds of intermittent fasting, and these are defined based on the amount of time you can or cannot eat during the day. Examples include the 16/8 diet, the 5/2 diet, and the alternate day diet described in more detail here. In addition, a recent study investigated the effect of alternate-day fasting, which is eating normally one day and then eating only 500 calories on the following day, on weight loss, weight maintenance, and risk for cardiovascular disease.
How was the study performed?
This study included a large number of people and looked at the effect of the diet plan for a long time (6 months). In this study, 100 people with a body mass index (BMI) that was greater than 25 (14 men and 86 women) were randomized into three different diet groups. The diet groups included an alternate day fasting (ADF) group, a calorie restriction (CR) group, and a group that did not change their diet (control). For the first six months, participants were encouraged to lose weight through following the different diets and then during the next six months, participants had the goal of maintaining their lost weight. Those in the ADF group ate 125% of their energy needs on feast days and 25% of needs on fast days, while those in the CR group ate 75% of their energy needs every day. The figure below shows more information about the timeline of the study.
How did the diets compare?
The findings of this study might not be what you would expect. Both the group that did alternate day fasting and the group trying to have a daily calorie restriction lost similar amounts of weight. Both groups lost around 6.8% of their body weight, which for a 200 lbs person equals 13.6 lbs. This may not seem like a lot of weight lost for six months of effort; however, studies have shown that even a 5% reduction in body weight can significantly impact overall health. Another key part of this study was comparing how well each group was able to follow the guidelines of the diet. This is important because one of the claims about intermittent fasting is that it is easier to follow than regular diets; however, in this study, that was not the case. More people left the study from the alternate-day fasting group (13 people) than the calorie restriction group (10 people). While this is only a difference of three people, it still does not support the claim that this intermittent fasting strategy was easier to follow.
Should I try intermittent fasting to lose weight?
This is a big question, and more research needs to be done about this question. If we are going to listen to this study's results, it shows that there is no magic solution to create weight loss once again. At the end of the day, it comes down to creating a calorie deficit over a long period of time. However, the people who followed intermittent fasting did lose weight. This means that if someone follows the same diet as the people in this study, they could expect similar results if they are overweight like the people in this study. This study defined if someone was overweight by using BMI (you can calculate your BMI here). BMI has its limitations but is very easy to use, which explains its widespread use. However, suppose you have type 1 or type 2 diabetes. In that case, you should talk to your doctor and seek out the help of a registered dietitian before attempting intermitted fasting, as you are at greater risk of complications.
Healthy weight loss that is maintained can be quite difficult. There is no simple answer, but if you decide to try intermitted fasting, the key point is that when you eat should not be the only thing to change. What you eat and who is supporting you in your diet change are also important points to consider.