Found in seed oils like canola and sunflower, linoleic acid (LA) has been the center of much debate in recent years, particularly whether the omega-6 polyunsaturated fatty acid leads to inflammation in the body.
According to the Cleveland Clinic, a diet high in seed oils with omega-6s skews the body’s balance of omega-6s and omega-3s, leading to inflammation that may cause chronic health conditions, including cardiovascular disease.
Dr. William Harris, PhD, president of the Fatty Acid Research Institute (FARI) and founder of independent laboratory OmegaQuant, argues otherwise.
“The problem is not the omega-6,” he said. “It’s the lack of the omega-3 that is ‘out of balance’. People love a black hat versus a white hat, a bad guy versus a good guy. Our understanding that even the omega-6s can produce anti-inflammatory molecules is fairly new.
“The [new] study contradicts the standard narrative that seems to never change despite years of data that our study confirms,” Dr. Harris said. “LA is simply not pro-inflammatory.”
The study was partly funded by a grant from the Soy Nutrition Institute Global with support from the United Soybean Board.
Decades of controversy
The roles that dietary fats play in the story of several chronic diseases, particularly cardiovascular disease, remain controversial. However, the only class of dietary fatty acids that is universally believed to be unhealthy are trans fatty acids, the researchers noted.
Counter to what the Cleveland Clinic advises, the American Heart Association issued a science advisory in 2009, as cited in the study, that stated omega-6 polyunsaturated fatty acid (n-6 PUFA) consumption should be at least 5% to 10% of energy. The Association went further, posing that “to reduce n-6 PUFA intakes from their current levels would be more likely to increase than to decrease risk for coronary heart disease.”
The researchers also reference a 2012 study by Johnson and Fritsche in the Journal of the Academy of Nutrition and Dietetics in which those researchers said there was “virtually no evidence” from randomized, controlled intervention studies among “healthy, non-infant human beings to show that addition of LA to the diet increases the concentrations of inflammatory biomarkers.”
Dr. Harris, an author on a 2024 study that appeared in The American Journal of Clinical Nutrition, and his colleagues studied data from the UK Biobank—which examines biological samples and health-related data of half a million people. They found a notable inverse associations between plasma LA levels and total and cause-specific mortality.
They added that the clinical implication of their findings would be to “encourage (at least not discourage) the consumption of foods rich in LA. This would be in direct opposition to voices currently advocating the removal of the richest source of LA in the diet, that is, seed oils.”
The controversy behind linoleic acid began more than four decades ago with the discovery that an omega-3 fatty acid blocked blood clot formation while its omega-6 cousin (arachidonic acid) caused clot formations, Dr. Harris explained.
“Then we learned that there was an omega-6 versus omega-3 competition for the same enzymes that can produce pro-inflammatory molecules,” he said. “And if you don’t have omega-3 around, the omega-6 fatty acids are free to be converted into proinflammatory mediators.”
Study details
The study published in the journal Nutrients recruited 2,777 participants, among them descendants of the original participants of The Framingham Heart Study. The well-known, longitudinal community-based cohort study began in 1948 and explores factors that contribute to heart disease. The scientists also recruited participants from The Framingham Omni cohort, established in 1994, to include a more ethnically diverse population in their research.
The participants had their blood drawn after a 12-hour fast, and their red blood cells were screened for fatty acid composition. The researchers looked at one urinary and nine serum biomarkers that represented several inflammatory pathways.
“Our community-based study identified small, significant, inverse associations between the red blood cell LA and arachidonic acid levels and six major biomarkers of inflammation (three in common: IL-6, ICAM-1, and MCP-1), representing a wide variety of inflammation pathways,” the researchers wrote. “Our results suggest that LA is more likely to be anti- than pro-inflammatory, and the present efforts to reduce its intake are ill advised.”
Dr. Harris said he hopes policymakers will follow the science instead of the negative narrative surrounding linoleic acid.
“It’s entirely possible that long-heating of seed oils to fry chicken nuggets and French fries could have adverse health effects (although that has not been clearly shown), but that has nothing to do with the presence of linoleic acid in the oils,” he said. “The LA is good. The frying may not be.”
Source: Nutrients, doi: 10.3390/nu17132076. “Red Blood Cell Omega-6 Fatty Acids and Biomarkers of Inflammation in the Framingham Offspring Study”. Authors: H.T.M. Lai, et al.
