Preferential Metabolic Improvement by Intermittent Fasting in People with Elevated Baseline Red Cell Distribution Width: A Secondary Analysis of the WONDERFUL Randomized Controlled Trial

Red cell distribution width (RDW) predicts cardiovascular outcomes, but it is unstudied with regard to intermittent fasting. In WONDERFUL trial subjects, the effect of the interaction between baseline RDW and intermittent fasting on changes in insulin and other cardiometabolic endpoints and the effect of fasting on changes in RDW were evaluated. The subjects enrolled were aged 21–70 years and were free of statins, anti-diabetes medications, and chronic diseases, and had ≥1 metabolic syndrome feature, as well as elevated low-density lipoprotein cholesterol. Subjects were randomized to 24-h, water-only fasting (twice per week for 4 weeks, once per week for 22 weeks) or 26 weeks of ad libitum eating. Subjects (N = 71; n = 38 intermittent fasting, n = 33 controls) had more substantial changes in insulin in intermittent fasting vs. controls (−3.45 ± 2.27 vs. 0.48 ± 3.55 mIU/L) when baseline RDW size distribution (RDW-SD) was ≥median (42.6 fL) than <median (−1.99 ± 2.80 vs. −1.08 ± 3.40 mIU/L) (p-interaction = 0.039). Results were similar but weaker for glucose, HOMA-IR, and metabolic syndrome score. RDW-SD (intermittent fasting: 1.27 ± 9.6 fL vs. control: −0.37 ± 1.76 fL, p = 0.34) was unchanged by fasting at 26 weeks. Intermittent fasting decreased insulin more in subjects with higher baseline RDW. RDW may identify individuals who derive the most health benefits from intermittent fasting and who have the most cause to adhere to a fasting regimen.