Does intermittent fasting affect appetite?

Researchers from NIHR Bristol BRC and the School of Psychological Science in the University of Bristol found no clear difference between the effects of intermittent fasting and continuous energy restriction on hunger, fullness, a person’s desire to eat or how much they think they can eat. Findings from this study were published in Nutrients and suggest that future research into intermittent fasting might benefit from using ecological momentary assessments to investigate how appetite fluctuates throughout the day.

Continuous energy restriction is a common weight loss method which involves restricting the number of calories you eat each day. Intermittent fasting is another, increasingly popular, method of losing weight. It involves alternating between periods of restricted and unrestricted eating and is usually divided into the following categories:

• Alternate-day fasting which involves alternating between a day of total food abstinence and a day of unrestricted eating
• 5:2 dieting which involves limiting food intake for two non-consecutive days per week and unrestricted eating for the rest of the week
• Time-restricted eating which involves eating within a certain window of hours each day and fasting during the remaining time

Researchers from NIHR Bristol BRC investigated whether there were any differences between how intermittent fasting and continuous energy restriction affected appetite. Appetite is our motivation to eat food and it includes feelings such as fullness, hunger and our desire to eat.

The research team reviewed data from 17 clinical trials comparing intermittent fasting and continuous energy restriction. They found no evidence to suggest intermittent fasting had a different effect to continuous energy restriction, when considering the number of calories study participants reported eating.

However, researchers were concerned that the wide variety of diets followed during the reviewed studies may have affected their results. Also, many of the studies only measured appetite once per day, which was often before breakfast. This means that they could not explore how these diets affect changes in appetite throughout the day.

Rebecca Elsworth, lead author, said:

“Intermittent fasting has been found to produce similar weight loss results to continuous energy restriction, as well as having some physiological benefits such as improvements in cardiometabolic risk factors and glucose metabolism. However, the psychological effects of fasting are less studied.

“Our results suggest that intermittent fasting does not affect appetite differently from continuous energy restriction interventions. This finding is not in line with existing narrative reviews, which have suggested that intermittent fasting may be beneficial for attenuating the increase in our drive to eat that can accompany weight loss.

“However, with appetite only being measured once before and once after the interventions, we cannot be sure how appetite is influenced over longer durations. Future intermittent fasting research could use ecological momentary assessment, an approach which involves repeated measurement of an individuals’ experiences in their natural environment. This would allow us to investigate the impact of fasting on peoples’ natural fluctuations in appetite, in real-life settings and throughout the course of the whole day.”