Intermittent fasting and health outcomes: an umbrella review of systematic reviews and meta-analyses of randomised controlled trials.
Level 1 - systematic review of randomized trials
Umbrella review of systematic reviews and meta-analyses of randomized controlled trials
PubMed 38500840 · doi:10.1016/j.eclinm.2024.102519
What was done
An umbrella review systematically searched PubMed, Embase, Web of Science, and Cochrane databases up to January 8, 2024, to synthesize systematic reviews and meta-analyses of randomized controlled trials (RCTs) assessing intermittent fasting (IF) on human health outcomes. Effect sizes were recalculated as mean differences (MD) or standardized mean differences (SMD) with 95% confidence intervals (CIs). Subgroup analyses evaluated adults with diabetes, overweight or obesity, and metabolic syndrome. Systematic review methodological quality was appraised with AMSTAR, and evidence certainty was evaluated with GRADE.
What was found
Twenty-three meta-analyses evaluating 351 associations across 34 health outcomes were included; 21 meta-analyses (91%) scored high confidence on AMSTAR. Of 103 statistically significant associations (p < 0.05), only 10 (10%) were supported by high GRADE certainty. In adults with overweight or obesity compared to a non-intervention diet, IF reduced waist circumference (MD = -1.02 cm; 95% CI: -1.99 to -0.06; p = 0.038), fat mass (MD = -0.72 kg; 95% CI: -1.32 to -0.12; p = 0.019), fasting insulin (SMD = -0.21; 95% CI: -0.40 to -0.02; p = 0.030), LDL-C (SMD = -0.20; 95% CI: -0.38 to -0.02; p = 0.027), total cholesterol (SMD = -0.29; 95% CI: -0.48 to -0.10; p = 0.003), and triacylglycerols (SMD = -0.23; 95% CI: -0.39 to -0.06; p = 0.007), while increasing fat-free mass (MD = 0.98 kg; 95% CI: 0.18 to 1.78; p = 0.016). Modified alternate-day fasting reduced fat mass (MD = -0.70 kg; 95% CI: -1.38 to -0.02; p = 0.044). In adults with overweight/obesity and type 2 diabetes, IF increased HDL-C versus continuous energy restriction (CER) (MD = 0.03 mmol/L; 95% CI: 0.01 to 0.05; p = 0.010), but was less effective than CER at reducing systolic blood pressure (SMD = 0.21; 95% CI: 0.05 to 0.36; p = 0.008).
Why it matters
Intermittent fasting yields modest benefits for anthropometric and lipid markers relative to non-intervention, but demonstrates limited distinct advantage over continuous calorie restriction and only a small minority of outcomes carry high-certainty evidence.
Limits
The abstract does not disclose total primary participant sample size, intervention durations, dietary adherence, adverse events, or long-term clinical endpoints. Secondary review synthesis may also involve overlapping primary trials across meta-analyses.
Cited by
- contradicts There are no clinical trials in humans showing a clear lifespan or health benefit from fasting.