Effects of Intermittent Fasting in Human Compared to a Non-intervention Diet and Caloric Restriction: A Meta-Analysis of Randomized Controlled Trials

Abstract

BackgroundThe popularity of applying intermittent fasting (IF) has increased as more and more people are trying to avoid or alleviate obesity and metabolic disease. This study aimed to systematically explore the effects of various IF in humans.MethodsThe randomized controlled trials (RCTs) related to IF vs. non-intervention diet or caloric restriction (CR) were retrieved in PubMed, Web of Science, Cochrane Library database, and Embase. Extraction outcomes included, but were not limited to, weight, body mass index (BMI), waist circumference (WC), fasting glucose, and triglyceride (TG).ResultsThis study includes 43 RCTs with 2,483 participants. The intervention time was at least 1 month, and the median intervention time was 3 months. Contrasting results between IF and non-intervention diet showed that participants had lower weight (weighted mean difference (WMD) = 1.10, 95% CI: 0.09–2.12, p = 0.03) and BMI after IF (WMD = 0.38, 95% CI: 0.08–0.68, p = 0.01). The WC of participants after IF decreased significantly compared with the non-intervention diet (WMD = 1.02, 95% CI: 0.06–1.99, p = 0.04). IF regulated fat mass (FM) more effectively than non-intervention diet (WMD = 0.74, 95% CI: 0.17–1.31, p = 0.01). The fat-free mass of people after IF was higher (WMD = −0.73, 95% CI: (−1.45)–(−0.02), p = 0.05). There was no difference in fasting blood glucose concentrations between participants in the after IF and non-intervention diet groups. The results of insulin concentrations and HOMA-IR, though, indicated that IF was significantly more beneficial than non-intervention diet (standard mean difference (SMD) = −0.21, 95% CI: 0.02–0.40, p = 0.03, and WMD = 0.35, 95% CI: 0.04–0.65, p = 0.03, respectively). Cholesterol and TG concentrations in participants after IF were also lower than that after a nonintervention diet (SMD = 0.22, 95% CI: 0.09–0.35, p = 0.001 and SMD = 0.13, 95% CI: 0.00–0.26, p = 0.05, respectively). IF outcomes did not differ from CR except for reduced WC.ConclusionIntermittent fasting was more beneficial in reducing body weight, WC, and FM without affecting lean mass compared to the non-intervention diet. IF also effectively improved insulin resistance and blood lipid conditions compared with non-intervention diets. However, IF showed less benefit over CR.

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.…”

“…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…”

“…Nine reviews compared lipid profiles between IF and CER and found no significant difference between the two in any of the parameters. [4][5][6]11,18,19,26,32,38 There was one exception where one review found CER to be superior to IF with respect to reducing total cholesterol and triglycerides, but equivalent with respect to reducing LDL. 44 Overall, no substantial conclusions can be drawn as a result of the inconclusive evidence on the outcomes of IF diets on lipid profiles.…”

Eating, diet, and nutrition for the treatment of non-alcoholic fatty liver disease

“…Also, Ramadan fasting reduced the gene expression of "fat-mass-andobesity-associated protein" (FTO) in overweight/obese individuals 153 , which has been associated with obesity 154 despite lower calorie intake 155 . However, it is currently a matter of debate whether IF (i.e., time-dependent calorie restriction) is more effective 156 or equally effective 157,158 than continuous calorie restriction (e.g., hypocaloric diet), and whether it is effective if no calorie restriction/dietary counselling is applied 159 . In the setting of type-2 diabetes mellitus 160 , close monitoring of diabetes medication and blood glucose is needed due to concerns about hypoglycemia 161 although TRF has also been shown to be effective and safe in overweight/obese patients with type-2 diabetes mellitus.…”

Does Timing Matter? A Narrative Review of Intermittent Fasting Variants and Their Effects on Bodyweight and Body Composition

“…IF is fundamentally a timing strategy that manipulates the placement and nature of feeding and fasting intervals, which can be stratified into two main categories: (1) intra-weekly fasting (alternate-day fasting/ADF, twice-weekly fasting/TWF) and (2) intra-daily fasting (early time-restricted eating/eTRE and delayed time-restricted eating/dTRE). A growing body of evidence indicates that IF is a viable alternative to daily caloric restriction (DCR), showing similar effectiveness for weight loss [ 3 , 4 ] and alleviating cardiometabolic risk factors [ 5 , 6 ].…”