Intermittent Fasting vs Caloric Restriction: Which Works Better for Heart Health?

Intermittent fasting has surged in popularity as an alternative to traditional calorie-counting diets, but rigorous head-to-head evidence comparing IF strategies against each other and against standard continuous energy restriction (CER) has been lacking. This network meta-analysis, commissioned to update European Association for the Study of Diabetes (EASD) guidelines, fills that gap using data from 99 randomised clinical trials and 6,582 adults across a range of health conditions.

Researchers searched Medline, Embase, and Cochrane databases through November 2024 and applied a frequentist random-effects network meta-analysis framework. The five dietary nodes compared were: alternate day fasting (ADF), time-restricted eating (TRE), whole day fasting (WDF), CER, and ad-libitum diet. The primary outcome was body weight; secondary outcomes spanned anthropometry, glucose metabolism, lipids, blood pressure, C-reactive protein, and liver markers. Evidence certainty was graded using GRADE methodology.

All IF strategies and CER reduced body weight compared with ad-libitum eating. Among IF approaches, ADF emerged as the strongest performer: it reduced body weight by a mean of 1.29 kg more than CER (moderate certainty), 1.69 kg more than TRE, and 1.05 kg more than WDF. For lipids, ADF lowered total cholesterol, triglycerides, and non-HDL cholesterol compared with TRE. Notably, TRE was associated with small increases in total cholesterol, LDL, and non-HDL relative to WDF—a finding warranting attention given TRE's widespread adoption. No significant differences were detected between any diet strategy for HbA1c or HDL cholesterol.

Duration of intervention modulated findings substantially. In shorter trials (under 24 weeks, n=76), ADF's advantages over other IF strategies and CER were apparent. In moderate-to-long-term trials (≥24 weeks, n=17), however, differences between active diet strategies largely disappeared, with all strategies showing benefit only relative to ad-libitum eating. This suggests that the early metabolic advantages of ADF may attenuate over time, possibly due to declining adherence or metabolic adaptation.

From a clinical standpoint, the results indicate that intermittent fasting is a broadly legitimate alternative to CER, particularly for patients who find continuous calorie restriction difficult to sustain. ADF may offer a modest short-term edge in weight and lipid outcomes. Longer, well-powered trials are urgently needed to determine whether any IF strategy maintains superiority over CER beyond six months, and to better characterise effects in specific patient populations such as those with type 2 diabetes or cardiovascular disease.