The effect of flaxseed oil after deep frying on lipid metabolism and gut barrier homeostasis

Flaxseed oil (FO) has been demonstrated its multiple beneficial effects in vivo due to high concentration of α-linolenic acid. The deterioration of FO can be triggered by high temperature heating during the deep frying process resulting in alteration of healthy properties. In this study, the effect of FO before and after deep frying on lipid metabolism and gut homeostasis of rats was investigated compared to deep-fried palm oil (DPO) treated group. Deep-fried flaxseed oil (DFO) treatment significantly enhanced the triglyceride accumulation in serum and liver tissues of rats. A greater increase of peroxides and proinflammatory cytokine levels was found in the serum of DFO treated rats compared to other groups. The histopathologic data indicated that DFO and DPO reduced the villus height of intestinal and colonic tissues and increased the inflammatory cell infiltration. The inflammatory cytokines (TNFα and IL-6) were enhanced and the key markers of epithelia colonic tissues (occludin and MUC-2) were suppressed in rats with DFO interventions, which is in consistency with histopathologic results. In addition, FO could increase the number of beneficial bacteria while the relative abundance of obesity and inflammatory-related bacteria was promoted by DFO treatment, including Ruminococcaceae, Prevotellaceae, and Selenomonadales. In conclusion, DFO intake had a significant impact on the disruption of gut barrier homeostasis, potentially worsening the dysbiosis than DPO. The beneficial effects of FO in vivo could be significantly reduced by extreme deep frying, which suggests the need for moderate cooking edible oils such as FO.