Supplementation with Polyunsaturated Fatty Acids as the Main Dietary Factor Is Associated with the Omega-3 Index in Lithuanian Professional Athletes

<b>Background/Objectives</b>: Nutrition is essential for both physiological and physical health. The study aimed to explore dietary habits, nutritional intake and supplementation in association with the indirect omega-3 index (ω-3I) magnitude in a cohort of professional athletes. <b>Methods</b>: A 3-day food record was used as an approach to document all the dishes and beverages consumed by athletes over three consecutive days. Additionally, in aiming to assess the dietary habits and supplementation as well as the estimated ω-3I, both a food frequency questionnaire and a valid equation proposed by Swiss scientists were applied. The body composition of athletes was assessed using the bioelectrical impedance analysis. <b>Results</b>: Given that carbohydrate-containing foods were relatively frequently consumed by athletes, the average daily carbohydrate content (5.5 g/kg of body weight/day) did not reach the minimum recommended limit. A Western pattern diet applied to professional athletes ensured a sufficient level of protein intake (1.7 g/kg of body weight/day) and resulted in the overconsumption of dietary fat (40.3% of energy intake (EI)), especially saturated fatty acids (FAs) (13.8% of EI). The frequency of the consumption of fish products was considered to fulfill the lowest rank, which in turn, led to the lowest average intakes for polyunsaturated (6.2% of EI), ω-6 (5.7% of EI), and ω-3 (0.3% of EI) FA. Also, the dietary ω-3 FA deficiency generated an unhealthy ω-6/ω-3 FA ratio of 18.4:1 which was not directly related to the intermediate-desirable level (5.5-9.8%) of the estimated ω-3I in a sample of professional athletes. <b>Conclusions</b>: Taking into account the predicted regression model which was adjusted for sports and sex, the estimated ω-3I was significantly and positively associated with the higher consumption of polyunsaturated FA supplementation (β 1.5, 95% confidence interval (CI): 1.3; 1.6, <i>p</i> < 0.001), fish products (β 1.1, 95% confidence interval (CI): 1.0; 1.2, <i>p</i> < 0.001), and the energy percentage obtained from the dietary ω-3 FA (β 0.8, 95% CI: 0.1; 1.6, <i>p</i> = 0.049) in a cohort of professional athletes. Therefore, whilst acknowledging that the increased fish consumption may serve as an equally strong potential predictor for the indirect ω-3I magnitude, the supplementation with polyunsaturated FA also becomes an important strategy for maintaining the optimum ω-3I levels among professional athletes.