Time-restricted eating with or without a low-carbohydrate diet improved myocardial status and thyroid function in individuals with metabolic syndrome: secondary analysis of a randomized clinical trial.

Background: Obesity and metabolic syndrome (MetS) have become urgent worldwide health problems, predisposing patients to unfavorable myocardial status and thyroid dysfunction. Low-carbohydrate diet (LCD) and time-restricted eating (TRE) have been confirmed to be effective methods for weight management and improving MetS, but their effects on the myocardium and thyroid are unclear.

Methods: We conducted a secondary analysis in a randomized clinical diet-induced weight-loss trial. Participants (N = 169) diagnosed with MetS were randomized to the LCD group, the 8 h TRE group, or the combination of the LCD and TRE group for 3 months. Myocardial enzymes and thyroid function were tested before and after the intervention. Pearson's or Spearman's correlation was assessed between functions of the myocardium and thyroid and cardiometabolic parameters at baseline.

Results: A total of 162 participants who began the trial were included in the intention-to-treat (ITT) analysis, and 57 participants who adhered to their assigned protocol were involved in the per-protocol (PP) analysis. Relative to baseline, lactate dehydrogenase, creatine kinase MB, hydroxybutyrate dehydrogenase, and free triiodothyronine (FT3) declined, and free thyroxine (FT4) increased after all 3 interventions (both analyses). Creatine kinase (CK) decreased only in the TRE (- 18 [44] U/L, P < 0.001) and combination (- 22 [64] U/L, P = 0.003) groups (PP analysis). Thyrotropin (- 0.24 [0.83] μIU/mL, P = 0.011) and T3 (- 0.10 ± 0.04 ng/mL, P = 0.011) decreased in the combination group (ITT analysis). T4 (0.82 ± 0.39 μg/dL, P = 0.046), thyroglobulin antibodies (TgAb, 2 [1] %, P = 0.021), and thyroid microsomal antibodies (TMAb, 2 [2] %, P < 0.001) increased, while the T3/T4 ratio (- 0.01 ± 0.01, P = 0.020) decreased only in the TRE group (PP analysis). However, no significant difference between groups was observed in either analysis. At baseline, CK was positively correlated with the visceral fat area. FT3 was positively associated with triglycerides and total cholesterol. FT4 was negatively related to insulin and C-peptide levels. TgAb and TMAb were negatively correlated with the waist-to-hip ratio.

Conclusions: TRE with or without LCD confers remarkable metabolic benefits on myocardial status and thyroid function in subjects with MetS.

Trial registration: ClinicalTrials.gov, NCT04475822.