Quantifying the impact of intermittent fasting on appetite

In a recent study published in the Nutrients Journal, researchers performed a meta-analysis to quantify the impact of intermittent fasting (IF) on appetite, compared to continuous energy restriction (CER).

Study: The Effect of Intermittent Fasting on Appetite: A Systematic Review and Meta-Analysis. Image Credit: AnikonaAnn/Shutterstock.com

Background

IF is an increasingly popular diet that involves alternating periods of energy restriction with periods of unrestricted energy intake and reportedly produces equivalent weight loss to CER interventions by attenuating an increase in appetite. In addition, IF has several physiological health advantages, including improvements in cardiometabolic functions and glucose utilization.

Moreover, conventional CER needs stringent dietary compliance without any flexibility. Therefore, IF regimes may be easier to sustain weight loss with increased acceptability among individuals.

Appetite encompasses feelings such as hunger, fullness, and desire to eat and may play a critical role in adherence to IF diets; however, the effects of IF on appetite are not well characterized.

About the study

In the present meta-analysis, researchers investigated whether IF could alter individuals’ appetites compared to CER.

The team searched five databases, EMBASE, MEDLINE, Scopus, Web of Science, and the Cochrane Central Register of Controlled Trials, between February 2021 and February of the following year for relevant randomized controlled trials (RCTs) without any language or publication date restrictions.

In addition, grey literature and unpublished studies were searched by contacting field experts, and the references of included studies were included.

Two reviewers screened the data independently and resolved disagreements by discussion. The primary study outcome was appetite, assessed using the visual analog scales (VASs) of fullness, hunger, eating desire, and prospective food consumption (PFC).

Secondary study outcomes included weight (kg), physical exercise, caloric intake (kcal/day), eating patterns-related questionnaire scores (e.g., the Three-Factor Eating Questionnaire), intervention compliance (%), and dropout rates.

Individuals of any age with any body mass index (BMI) value who practiced any IF regime [such as alternate day fasting (ADF), the 5:2 diet, and time-restricted eating (TRE)] for any duration were included.

The quality of the evidence was assessed using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach. A random effects meta-analysis was performed on change-from-baseline appetite ratings.

In addition, sensitivity analyses were performed by excluding records with imputed findings and a meta-analysis of the fixed-effects type.

Results

Initially, 4,390 studies were identified, from which 1,590 duplicate records were removed, and 2,800 records underwent abstract and title screening, following which 2,430 studies were excluded, and the complete text of 370 studies was analyzed.

After excluding 251 studies not measuring appetite, 20 non-RCT studies, 59 studies lacking the CER comparator, nine lacking the IF intervention, and seven ongoing RCTs, 17 studies were considered for the final analysis.

The RCTs comprised 1,111 adults practicing IF or CER over two weeks to one year with BMI values equal to or greater than 24.0 kg/m². The team found no significant evidence of IF affecting hunger [weighted mean difference (WMD) −3.0], fullness (WMD 3.1), desire to eat (WMD −3.9), or PFC (WMD −2.8) differently than CER interventions.

Similar results were obtained in the subgroup analysis for the different types of IF regimes. Among the included studies, four RCTs had medium bias risks, whereas 13 had high risks. Appetite measurement varied across studies, and the quality of evidence was very low for fullness, hunger, desire to eat, and PFC.

In the sensitivity analysis, the direction of effect was the same; however, the fixed-effects meta-analysis findings showed that IF increased fullness, reducing the desire to eat, compared to CER interventions.

High bias risks may be due to the nature of dietary interventions. It may not often be possible to blind participants or those delivering the health intervention, which could introduce expectation bias in the intervention group.

Moreover, appetite was evaluated using self-reported data. The wide variations in caloric limitation protocols and their effects (for example, varied daily caloric intake) could also influence the study findings.

Conclusion

Overall, the study findings indicated that intermittent fasting does not mitigate an increase in our appetite that is often linked to continuous energy restriction, with no reduction in fullness, hunger, eating desire, or PFC.

The findings contrast those reported in previous studies, likely due to differences in the analysis approach.

Further research could include momentary ecological assessments to evaluate fluctuations in appetite throughout the day and subtle appetite modifications related to IF interventions.

Written by

Pooja Toshniwal Paharia

Dr. based clinical-radiological diagnosis and management of oral lesions and conditions and associated maxillofacial disorders.