Can linoleic acid avert onset of type 2 diabetes?
Long-term dietary intake of linoleic acid may help prevent the development of type 2 diabetes (T2D), with the linoleic acid metabolite arachidonic acid having no harmful effects, according to a meta-analysis of 20 prospective cohort studies.
The analysis involved 39,740 adults without T2D at baseline, among whom 4,347 developed T2D during 366,073 person-years of follow-up. Pooled data on biomarkers of linoleic and arachidonic acid revealed an inverse association between baseline linoleic acid levels and incidence of T2D overall (risk ratio [RR] per interquintile range, 0.65; 95 percent CI, 0.60 to 0.72; p<0.0001). [Lancet Diabetes Endocrinol 2017;5;965–974]
“Associations between linoleic acid biomarkers and T2D were generally similar in different lipid compartments, including phospholipids, plasma, cholesterol esters and adipose tissue,” the authors noted.
In contrast, baseline levels of arachidonic acid were not significantly associated with the risk of incident T2D overall (RR per interquintile range, 0.96; 0.88 to 1.05; p=0.38) or in individual lipid compartments, with the exception of plasma (RR per interquintile range, 0.73; 0.62 to 0.86; p=0.0003).
Of note, prespecified potential sources of heterogeneity, such as age, body mass index, sex, race, aspirin use and omega-3 polyunsaturated fatty acid (PUFA) levels, among others, did not significantly modify the associations observed between linoleic and arachidonic acid levels and incident T2D.
“Our analysis provides novel findings that, when combined with in-vitro experimental and shorter-term interventions for metabolic risk factors, linoleic acid has an additional role for prevention of T2D in healthy populations,” the authors said.
When incorporated into phospholipids, linoleic acid is said to alter membrane fluidity and potentially modulate insulin receptor activity. This is supported by previous studies reporting that dietary PUFAs improve glycaemia, insulin resistance and insulin secretion capacity compared with carbohydrate, saturated fat and even monounsaturated fat for some endpoints. [Diabetologia 2015;58:282–89; PLoS Med 2016;13:e1002087]
“Because dietary linoleic acid intake correlates with levels of circulating and tissue linoleic acid, our biomarker-based findings extend and expand these previous results by providing evidence that linoleic acid might have long-term benefits for preventing the onset of T2D, supporting clinical recommendations to increase dietary intake of linoleic acid-rich vegetable oils,” the authors pointed out.
The established benefits of PUFAs for blood cholesterol levels and glucose-insulin homoeostasis, notwithstanding, some scientists maintain that omega-6 PUFA is harmful for health. Such harm is postulated to involve the conversion of linoleic acid to arachidonic acid, which is considered proinflammatory and potentially detrimental to glucose metabolism, weight regulation and eating behaviour. [Prostaglandins Other Lipid Mediat 2016; 125: 90–99]
However, “our findings do not corroborate concerns about potential harmful effects of arachidonic acid,” the authors said. “This is consistent with a recent systematic review reporting that levels of the biomarker arachidonic acid were associated with lower incidence of coronary heart disease.” [Ann Intern Med 2014; 160: 398–406]