Fish oil is a dietary source of omega-3 fatty acids and is one of the most commonly consumed dietary supplements. The World Health Organization (WHO) recommends eating 1–2 portions of fish per week because the omega-3 fatty acids in fish provide many health benefits, such as supporting heart health, aiding in weight loss, and even reducing inflammation. Now, new research from a team led by a University of Georgia scientist reports that taking fish oil only provides health benefits if you have the right genetic makeup.

The findings were published in the journal PLOS Genetics in a paper titled, “Genome-wide association study of fish oil supplementation on lipid traits in 81,246 individuals reveals new gene-diet interaction loci,” and led by Kaixiong Ye, PhD, assistant professor of genetics in the Franklin College of Arts and Sciences.

“Fish oil supplementation is widely used for reducing serum triglycerides (TAGs) but has mixed effects on other circulating cardiovascular biomarkers,” wrote the researchers. “Many genetic polymorphisms have been associated with blood lipids, including high- and low-density-lipoprotein cholesterol (HDL-C, LDL-C), total cholesterol, and TAGs. Here, the gene-diet interaction effects of fish oil supplementation on these lipids were analyzed in a discovery cohort of up to 73,962 UK Biobank participants, using a 1-degree-of-freedom (1df) test for interaction effects and a 2-degrees-of-freedom (2df) test to jointly analyze interaction and main effects.”

“We’ve known for a few decades that a higher level of omega-3 fatty acids in the blood is associated with a lower risk of heart disease,” added Ye. “What we found is that fish oil supplementation is not good for everyone; it depends on your genotype. If you have a specific genetic background, then fish oil supplementation will help lower your triglycerides. But if you do not have that right genotype, taking a fish oil supplement actually increases your triglycerides.”

The researchers examined four blood lipids—high-density lipoprotein, low-density lipoprotein, total cholesterol, and triglycerides—that are biomarkers for cardiovascular disease. The data for their sample of 70,000 individuals were taken from UK Biobank.

After running over 64 million tests, their results revealed a significant genetic variant at gene GJB2. Individuals with the AG genotype who took fish oil decreased their triglycerides. Individuals with the AA genotype who took fish oil slightly increased their triglycerides.

The new findings may also shed light on previous trials, that have reported that fish oil provides no benefit in preventing cardiovascular disease.

“One possible explanation is that those clinical trials didn’t consider the genotypes of the participants,” Ye said. “Some participants may benefit, and some may not, so if you mix them together and do the analysis, you do not see the impact.”

Moving forward, the researchers will be directly testing the effects of fish oil on cardiovascular disease.

“Our study identifies novel gene-diet interaction effects for four genetic loci, whose effects on blood lipids are modified by fish oil supplementation. These findings highlight the need and possibility for personalized nutrition,” concluded the researchers.

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