Balancing Omega-3 and Omega-6 PUFA: We are What We Eat
Based on recommendations to replace animal fats with vegetable oils, there has been a 3-fold increase in the consumption of the omega-6 PUFA, linoleic acid (LA, 18:6n-6). Shorter chain omega-3 and omega-6 PUFAs compete for desaturation/elongation enzymes to produce long-chain PUFA. In 1992, Lands and colleagues showed that competition between omega-3 and omega-6 PUFA changed the abundance of eicosanoid in blood and tissues. Because <5% of ALA is converted to long-chain PUFA, eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), the best solution is to increase the intake of pre-formed EPA and DHA.
Twenty-some years later, MacIntosh and colleagues hypothesized that lowering LA intake could potentially augment the health benefits of omega-3 PUFA. To test this hypothesis, 67 subjects consuming a typical high omega-6 and low omega-3 diet were randomized to: 1) low n-6/average n-3 diet [ALA ≤ 0.6% energy, ARA = 60mg/d, EPA+DHA= 125mg/d, Total PUFA=2.5% energy] or 2) low n-6/high n-3 diet [ALA ≥1.5% energy, ARA=150mg/d, EPA+DHA ≥ 1000mg/d, Total PUFA=4.5% energy]. The study design was a 12 week, parallel-group, randomized dietary intervention.
First, the authors demonstrated it is possible to find palatable foods to obtain a low linoleic acid diet in 2013. However, it is not easy, particularly in the US, to reduce LA intake by 50%. Second, reducing LA intake increased the EPA and DHA content of red blood cells (RBC). It did not change AA levels. The authors conclude that reducing LA intake raises EPA and DHA RBC levels. While the result is clear, the effect cannot be assigned to a single PUFA , e.g. LA, because the dietary intakes of LA, EPA + DHA were changed relative to baseline (typical American diet).
Eating more omega-3 and less omega-6 is prudent (Lands et al, 1992). To help do this, Dr Bill Lands invented the Omega-3 Balance Scores. Choose foods with higher scores to increase your omega-3 status.
As the old adage goes, balance and moderation are important.
Lands WEM, Libelt B, Morris A, Kramer NC, Prewitt TE, Bowen P, Schmeisser D, Davidson MH, Burns JH. Maintenance of lower proportions of (n-6) eicosanoid precursors in phospholipids of human plasma in response to added (n-3) fatty acids. 1992 Biochem Biophys Acta 1180:147
Brenna JT. Efficiency of conversion of α-linolenic acid to long chain n-3 fatty acids in man. 2002 Curr Opin Clin Nutr doi: 10.1097/00075197-200203000-00002.
MacIntosh BA, Ramsden CE, Faurot KR, Zamora D, Mangan M, Hibbeln JR. Mann JD. Low-n-6 and low-n-6 plus high-n-3 diets for use in clinical research. 2013 Br J Nutr doi:10.1017/S0007114512005181
Lands B. Prevent the cause, not just the symptoms. 2011 Prostaglandins Lipid Mediators doi:10.1016/j.prostaglandins.2011.07.003