Know your diet — Long-chain polyunsaturated fatty acids (PUFA) come in two forms: omega-3 or omega-6 PUFA. | By Jane Brown

These long-chain polyunsaturated fatty acids differ by having the terminal double bond in the acyl chain located either three or six carbon atoms from the terminal methyl group. See picture below:

More about omega-3 PUFA as summarized by Djuricic I. and Calder PC; 2023; PMID: 36662586, “ɑ-linolenic acid (ALA; 18:3n-3) is referred to as an essential fatty acid because humans, like other animals, do not express the enzyme delta-15 desaturase required to introduce the ω-3 double bond and therefore cannot synthesize ALA de novo.”

In their review, Burdge GC and Calder PC; 2002; PMID: 16188209, provides trace data indicating that 𝛼-linolenic acid (Ala C-18:3n-3) is a precursor to the longer chain eicosapentaenoic acid (EPA, C-20:5n-3) but may not be a precursor to the longer chain docosahexaenoic acid (DHA, C-22:6n-3). This elongation mechanism follows the work of Cunnane SC et al; 1994; PMID: 8189246, and can be important for pregnant and breastfeeding women, who may need additional DHA for fetal and newborn brain development. Ultimately, the question is: “Should pregnant women increase their consumption of oily fish, take supplements containing DHA, or eat more walnuts?” (A rich source of linolenic acid). Equally important in answering this question are the following estimates:

“Adipose tissue represents approximately 15% of body mass in males and 23% of body mass in females. Thus, the incorporation of 𝛼-linolenic acid (Ala C-18:3n-3) into this storage pool represents a potentially important pathway for dietary Ala disposition and a reserve pool available for mobilization during periods of increased demand. Ala represents approximately 0.7% of total fat Neutralizes fatty acids in fat tissue in men and women, while the concentration of DHA is about 0.1% and EPA is practically undetectable. Thus, it can be calculated that in a 75 kg man with a fat mass of 15%, the whole body reserves of Ala in adipose tissue would be approximately 79 grams (roughly equivalent to typical consumption over 53 days). Likewise, in a 65 kg woman with a fat mass of 23%, whole body ALA reserves in adipose tissue would be approximately 105 grams (roughly equivalent to a typical intake over 70 days).” See also Burdge GC and Wootton SA; 2002; PMID: 2323090.

Using samples from the UK Biobank (n=85,425), Zhang Y. et al; 2024; PMID: 38578269, “The risk was estimated for all three mortality outcomes, which increased with increasing ratio of omega-6/omega-3 PUFAs (all trend <0.05). Comparing the highest quintiles to the lowest, individuals had a 26% (95% CI, 15-38%) higher overall mortality rate, and a 14% (95% CI, 0-31%) higher rate." Cancer mortality, and 31% (95% CI, 10-55%) higher than mortality from CVD. These risk estimates were arrived at after adjusting for relevant risk factors. In conclusion, the authors wrote: “Cohort studies show an association between higher intakes of eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) or higher levels of of EPA and DHA in the body and lower the risk of cardiovascular disease (CVD), especially coronary heart disease and myocardial infarction, cardiovascular mortality and cancer mortality in the general population.”