Intermittent Energy Restriction for Weight Loss: A Systematic Review of Cardiometabolic, Inflammatory and Appetite Outcomes

Abstract

Current guidelines for obesity treatment recommend reducing daily caloric intake for weight loss. However, long-term weight loss continues to be an issue in obesity management. Alternative weight loss strategies have increased in popularity, such as intermittent energy restriction (IER), a type of eating pattern with periods of fasting alternating with unrestricted eating. The effects of IER on weight loss, cardiovascular risk factors, inflammation, and appetite are not clear. The purpose of this systematic review was to analyze short- (<24 weeks) and long-term (≥24 weeks) effects of IER on anthropometric, cardiometabolic, inflammatory, and appetite outcomes in adults with overweight/obesity. PubMed, CINAHL, Embase, and PsycInfo were searched from inception to July 2020. Human randomized controlled trials (RCTs) on IER with participants with a body mass index ≥25 kg/m2 were included in this review. A total of 42 articles (reporting on 27 different RCTs) were included. In short-term studies, IER showed pre-to-post treatment improvements in eight of nine studies that assessed weight. Weight outcomes were sustained in the long-term. However, no significant long-term between group differences were observed in fat mass, other anthropometric, cardiometabolic, inflammatory, or appetite outcomes. Compared to continuous energy restriction (CER), IER showed no significant long-term differences in anthropometric, cardiometabolic, inflammatory, or appetite outcomes in included studies. More long-term studies are needed to assess the benefits of IER on health outcomes.

Metabolic changes with intermittent fasting

“…When compared with an ad libitum diet, 10 reviews found fasting glucose to be significantly reduced during IF, 10,16,21,22,24,29,30,[40][41][42] whereas nine reviews found that there was no significant difference compared to an ad libitum diet. 5,6,13,17,20,25,26,28,37 All seven reviews that reported HbA1c levels found no significant difference between IF and control groups. 5,14,21,25,29,30,37 Four of these reviews did not include any participants with T2D and therefore most participants did not have any glucose abnormalities at baseline.…”

“…The remaining review that included participants with T2D did not specify a count. 26 Ten reviews found no difference in fasting glucose between IF and CER. One review found mixed results attributed to the heterogeneity of studies.…”

“…6,11,12,[15][16][17]20,21,[23][24][25]27,29,30 IF versus CER Nineteen reviews found a comparable weight loss following IF and CER. [4][5][6]11,18,19,23,[25][26][27][31][32][33][34][35][36][37][38][39] In terms of BMI change, five reviews compared IF to CER, finding no significant difference between the two interventions. 11,25,27,38,39…”

“…14,37 Twelve reviews analysed fasting insulin levels in IF versus an ad libitum diet. The number of reviews that identified no difference 13,20,24,26,28,42 was equal to the number of reviews that identified an improvement compared to control. 6,15,25,29,30,40 Similarly to effects on insulin levels, evidence on insulin resistance in the IF group compared to ad libitum groups was inconclusive.…”

“…Five reviews found no significant differences between the two groups. 19,26,27,32,38 Ezzati et al 4 found inconsistent results across different IF variations. One meta-analysis found a significant effect of IER compared to CER on insulin levels (WMD = −3.66 pmol/l, 95% confidence interval = −9.12 to −0.19, p = 0.041), although only 182 participants were included in this analysis.…”