The level of post-exercise inflammatory response induced by oxidative stress may depend on the fatty acid content of red blood cells. Twenty-three ultramarathoners were randomly assigned to two groups: a lipid complex supplementation group (SUPL) (n = 12, 1200 mg/day for 30 days) and olive oil intake a placebo group (PL) (n = 11, 1200 mg/day for 30 days). Participants performed eccentric exercise (30 min of downhill running at 70% \(\:\dot{\text{V}}\) O2 peak). Fatty acid composition in red blood cells, blood markers of antioxidant balance and inflammation were assessed at rest, immediately post-exercise, and 1-hour and 24-hour post-exercise. After supplementation, both the supplementation and placebo groups showed significant changes in the AA/EPA ratio (Z = −3.06, p = 0.002, r = 0.88 in SUPL and Z = −2.94, p = 0.003, r = 0.89 in PL), and the SUPL group showed lower malondialdehyde post-exercise level (5.2 ± 0.6 vs. 7.1 ± 1.7 µmol/L) compared to the PL group. The lipid complex in the SUPL group significantly increased superoxide dismutase post-exercise level (1371.6 ± 107.9 U/gHb vs. 1720.8 ± 312.0 U/gHb) and decreased catalase and reduced glutathione rest levels. Lipid complex supplementation derived from Perna canaliculus L. can induce beneficial changes in AA/EPA ratio and post-exercise superoxide dismutase activity in athletes’ blood.
