Effects of 12 Weeks of Calanus Oil Supplementation on Cardiac Diastolic Function in Obese and Prediabetic Women—A Pilot Study

Background/Objectives: In early-stage diabetes, diastolic dysfunction is an initial indicator of heart failure and is linked to altered glucose metabolism, including in prediabetes. Based on initial evidence that Calanus oil, derived from Calanus finmarchicus, which is rich in omega-3 polyunsaturated fatty acids and other bioactive compounds, benefits metabolic and cardiorespiratory health, this proof-of-principle study aimed to assess whether Calanus oil improves diastolic function in prediabetic women. Methods: Twenty middle-aged, obese women with prediabetes and no history of cardiac complications were enrolled and received 4 g/day of Calanus oil, providing 276 mg EPA + 256 mg DHA, for 12 weeks. Systolic and diastolic cardiac function, including the E/A ratio (E/A), was assessed by echocardiography. In addition, central blood pressure (BP) and pulse wave velocity (PWV) were analyzed by oscillometry. Metabolic health was evaluated using composite markers, including the metabolic syndrome severity score (Met-S score) and the triacylglycerol glucose–waist-to-height ratio (TyG-WHtR). Results: E/A was significantly improved (p = 0.023) following 12 weeks of Calanus oil supplementation. Furthermore, a significant improvement in metabolic health, indicated by a reduced Met-S score and a lower TyG-WHtR, was noticed (p < 0.001, respectively), reflecting decreased metabolic syndrome severity and enhanced insulin sensitivity. In addition, a significant reduction in diastolic BP, resting heart rate (p = 0.047), but not PWV or systolic BP (all p > 0.05) was observed. The improvement in E/A was associated with improved insulin sensitivity, as reflected by a decrease in the TyG-WHtR (p = 0.014). Conclusions: These exploratory findings suggest that Calanus oil supplementation in pre-diabetic women might improve central diastolic haemodynamics, accompanied by an overall improvement in metabolic health. However, the absence of a placebo control group limits definitive conclusions.