Intermittent fasting (IF) is associated with measurable weight loss and metabolic benefits in adults with overweight or obesity, researchers reported in JAMA Network Open.
The investigators conducted an “umbrella” review of several other meta-analyses of randomized clinical trials (RCTs) to more specifically define the benefits associated with IF on obesity-related health outcomes.
PubMed, Embase, and the Cochrane database were searched from inception to January 12, 2021 to identify relevant meta-analyses of RCTs involving IF. The Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) criteria were used to assess the quality of evidence per effect.
The study authors selected 11 meta-analyses, which included 130 RCTs (45 unique RCTs) with a median (interquartile range [IQR]) sample size per RCT of 38 (24-69 participants) studies and follow-up of 3 (2-5) months. A total of 104 unique associations were identified, with a median (IQR) of 4 (3-5) studies per association and median IQR sample size of 266 (119-423) participants.
Among the types of IF included in the study were zero-calorie alternate-day fasting, modified alternate-day fasting (MADF), the 5:2 diet (in which participants fasted for 1 to 2 consecutive or nonconsecutive days per week), and time-restricted eating, which involved fasting for 12 to 24 hours per day. Associations with IF included 42 (40%) anthropometric measures (such as body mass index [BMI]), 34 (33%) lipid profile outcomes, 15 (14%) glycemic profile outcomes, 10 (10%) blood pressure outcomes, and 1 outcome associated with C-reactive protein, adiponectin, leptin, and ghrelin levels.
According to GRADE criteria, a majority of the associations were supported by very low strength of evidence (75 associations [72%]). Other associations were supported by low (22 associations [21%]), moderate (6 associations [6%]), and high level of evidence (1 association [1%]).
Of the 104 associations, 28 (27%) were statistically significant according to a random-effects model, of which 17 were supported by a very low level of evidence (61%), followed by low (5 associations [18%]), moderate (5 associations [18%]), and high (1 association [4%]) levels of evidence.
The associations primarily involved adults with overweight or obesity and showed beneficial outcomes associated with intermittent fasting for BMI, body weight, fat mass, low-density lipoprotein cholesterol, total cholesterol, triglyceride level, fasting plasma glucose, fasting insulin, homeostatic model assessment for insulin resistance, and blood pressure. Intermittent fasting was also associated with reductions in fat-free mass.
Of the 7 associations supported with moderate to high-quality evidence, 6 were statistically significant. One association was supported with high-quality evidence, as a meta-analysis found that MADF for 1 to 2 months was associated with lower BMI in healthy adults and adults with overweight, obesity, or nonalcoholic fatty liver disease (NAFDL) vs regular diet (mean difference, −1.20; 95% CI, −1.44 to −0.96).
The investigators noted several study limitations. The meta-analyses did not include adverse outcomes, which prevented the researchers from comprehensively evaluating the benefits and safety aspects of IF. The study also did not include meta-analyses of observational studies of IF, which may have a longer follow-up, and most of the RCTs were limited to short follow-up durations and relatively small sample sizes.
“This review suggests that intermittent fasting may have a beneficial role in improving anthropometric and cardiometabolic outcomes, especially for adults with overweight or obesity,” the study authors concluded.
Disclosure: Some study authors received personal or professional fees. Please see the original reference for a full list of authors’ disclosures.
Patikorn C, Roubal K, Veettil SK, et al. Intermittent fasting and obesity-related health outcomes: an umbrella review of meta-analyses of randomized clinical trials. JAMA Netw Open. 2021;4(12):e2139558. doi:10.1001/jamanetworkopen.2021.39558