Healthy adults on the higher-LA diet had marked reductions in eicosapentaenoic acid (EPA), as measured by EPA-derived oxylipin species.
“These findings provide direct human evidence that LA intake not only contributes to membrane composition but also exerts competitive control over a shared enzymatic pathway, with downstream consequences for inflammatory signaling capacity,” wrote researchers in the USA in the journal Nutrients.
They noted that their findings are particularly relevant to socioeconomically disadvantaged populations who rely on ultra-processed foods high in LA, and may have lower dietary intake of omega-3s.
The importance of omega-6 to omega-3 ratios
Linoleic acid (LA)-rich vegetable oils such as soybean and corn oil are widespread in the modern Western diet and are a source of omega-6 fatty acids.
The increase in the use of these oils has led to an imbalance between omega-6 and omega-3 fatty acids and is thought to contribute to the incidence and progression of chronic diseases.
In contrast, omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are recognized as anti-inflammatory and protective against many chronic diseases, including cardiovascular disease and cognitive decline.
Although omega-6 and omega-3 metabolites have opposing actions, they are synthesized via a common enzymatic pathway.
Animal studies have shown that increasing dietary LA suppresses the conversion of alpha-linolenic acid (ALA) to EPA and DHA, and enhances arachidonic acid (ARA) synthesis, thereby potentially contributing to inflammation.
The current study aimed to provide human data about how dietary LA modulates these inflammatory pathways.
Study details
52 healthy adults completed the study and were randomly assigned to either a low-LA diet (2.5% energy) or a high-LA diet (10.0% energy) for 12 weeks. The intervention supplied at least 95% of participants’ daily fat intake, which accounted for 25–30% of total caloric intake.
Safflower variants were used to manipulate dietary LA, and flaxseed oil, a source of ALA, was provided in equal amounts to both study groups.
The researchers collected anthropometric and physiological measurements and analyzed blood samples for fatty acids and oxylipins.
The results showed that the high-LA diet was associated with marked reductions in EPA and eicosatetraenoic acid (ETA) concentrations compared with the low-LA diet.
“Docosapentaenoic acid (DPA) was also significantly lower in weeks 4 and 8. In contrast, levels of the n-6 HUFA arachidonic acid (ARA) did not differ with dietary LA exposure,” the researchers wrote.
“HUFA and oxylipin analyses revealed that higher dietary LA markedly increased the ratios of ARA to EPA and ARA- to EPA-derived oxylipin species, shifting the lipid mediator balance toward a more n-6-dominant inflammatory profile,” they concluded.
The researchers noted the challenges of rigorously monitoring and supporting participants to achieve the required dietary fatty acid ratios, which led 16% to withdraw from the study. They recommended future studies that are adequately powered and able to stratify by fatty acid desaturase genes, which can modulate individual responses to fatty acid intake.
Source: Nutrients; doi: 10.3390/nu18111814; ““Effect of Dietary Linoleic Acid Intake on Eicosapentaenoic Acid Status and Lipoxygenase-Mediated Oxylipin Biosynthesis in Healthy Adults: A Randomized Controlled Trial.” Authors: S. Sergeant et al.
