Using the Best Methods to Measure Health Effects of Omega-3s
Are you getting enough of the omega-3 (n-3) long-chain polyunsaturated acids (LCPUFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)? Most people aren’t. Why? Because they do not eat the 2-3 servings of fatty fish recommended per week. And even if they do, this may not be sufficient because the fatty acid composition of the fats in our body reflects the profile of ALL the fat consumed.
Patterson and colleagues analyzed the fatty acid profile of whole blood, plasma and red blood cells (RBC) isolated from 45 men and women who had been asked to consume 1g of EPA +DHA daily for a year. They report that the % EPA and % DHA increased with supplementation. As previously shown, fatty acid profiles of RBC more accurately reflect dietary intake. They concluded that the percentage of DHA in red blood cells was the best measure of dietary intake, or as they word it of non-adherence.
Why is this important? Last summer, in a subset of men participating in a prostate cancer prevention trial (SELECT), Brasky et al (2013) compared quartiles of plasma fatty acid levels at baseline and associated these with an increased risk of developing prostate cancer over the next 6 years. The headlines from this one study may have scared some people. It shouldn’t. Why? Because Brasky and colleagues correlated a single baseline plasma blood sample in men diagnosed with prostate cancer and their corresponding frequency-matched controls to calculate a hazards ratio (HR). From this single blood sample, they drew conclusions regarding omega-3 fatty acids and prostate cancer risk. However, Patterson et al (2014) report that fatty acid profiles of plasma samples are the poorest predictor of LCPUFA intake. In other words, plasma fatty acid percentages are not very accurate or representative. As written by MacKay and Ritz (2013), the study by Brasky et al (2013) should not change clinicians’ dietary recommendations of prescribing patterns.
What should we do? Should we still use omega-3 fatty acids supplements? When considering fat intakes and health outcomes, the first consideration is the total amount (mass) of fat being consumed. More is not better. Then one should consider the type (balance) of fatty acids being consumed. In other words, the percentages of total fat represented by types of fatty acids – trans, saturated, monounsaturated, omega-3 and omega-6 LCPUFA. High intakes of trans fatty acids, saturated fatty acids, and especially the omega-6 fatty acid, α-linoleic acid (ALA), need to be balanced by consuming more omega-3 LCPUFA, especially EPA and DHA, for optimal health.
Ten years ago, Wijendran and Hayes (2004) wrote that a dietary fatty acid ratio of omega-6/omega-3 ratio of ~6:1 was desirable. Today, Patterson et al (2014) affirm the importance of using RBC fatty acid percentages to evaluate the relationship between fatty acid intakes and health outcomes. It isn’t accurate to use whole blood or plasma fatty acid percentages when giving nutrition guidance.
As a consumer, don’t worry too much about these details. Just remember that most of us don’t consume enough EPA and DHA compared to the amount of trans, saturated, and α-linoleic acid (an omega-3) fatty acids.
Patterson AC, Metherel AH, Hanning RM, Stark KD. The percentage of DHA in erythrocytes can detect non-adherence to advice to increase EPA and DHA intakes. 2014 Br J Nutr doi:10.1017/S0007114513002225
MacKay D, Ritz BW. Do fatty acids really increase risk of prostate cancer? 2013 Natural Med J
Brasky TM, Darke AK, Song X, Tangen CM, Goodman PJ, Thompson IM, Meyskens Jr FL, Goodman GE, Minasian LM, Parnes HL, Klein EA, Kristal AR. Plasma phospholipid fatty acids and prostate cancer risk in the SELECT trial. 2013 JNCI doi:10.1093/jnci/djt174
Wijendran V, Hayes KC. Dietary n-6 and n-3 fatty acid balance and cardiovascular health. 2004 Ann Rev Nutr doi:10.1146/annurev.nutr.24.012003.132106.