A Standardized Approach to Measuring Human Fatty Acid Concentrations would help Everyone
Depending upon the type of fat we consume, experts write that dietary fat is not so bad for us. In fact, the debate about ‘added sugar’ is probably driven by nutrition guidance beginning in the 1980’s that vilified fat, especially saturated fat. As a consequence, carbohydrates represent a greater proportion of calories consumed. As percent of calories from carbohydrate goes up, percent as fat goes down. Which nutrient is at fault for increased obesity and related disease? The answer lies in the details.
Did total calorie intake change? Does type of fat (or carbohydrate) affect the outcome? There are three main classes of fat: saturated, mono- and poly-unsaturated fatty acids. The latter consists of omega-3 (n-3) and omega-6 (n-6) fatty acids.
Omega-3 fatty acids (ω-3) are considered ‘essential’ because human bodies have limited capacity to produce eicosapentaenoic acid (EPA) and docosahexaenoic (DHA) fatty acids from other dietary sources of fat. Because of structural differences, the inflammatory potential of signaling molecules differ when derived from ω-3 than ω-6 fatty acids. Adverse ω-3 status is especially detrimental during fetal and early child development and potentially after severe traumatic brain injury (TBI).
Standards to measure and report fatty acid status would help researchers determine optimal ω-3 concentrations, i.e. criterion of adequacy. Because red blood cell (RBC) fatty acid composition reflects long term dietary intake of EPA + DHA, Harris and von Shacky proposed the RBC omega-3 index in 2004.
The omega-3 index is a relative measure of EPA + DHA divided by total fatty acid measured (% EPA+DHA/total fatty acids). Researchers typically do not report actual fatty acid concentrations (either as traditional units of µg/dL or SI units of µmol/L). For example, Roy et al, 2015 report quantification methods but not actual fatty acid concentrations.
Without reporting fatty acid concentrations (rather than % wt/wt) and being specific about the fatty acids quantified, comparisons among studies are limited. The field is also hampered by some studies reporting data from whole-blood concentrations whereas others report on plasma or RBC. A lack of standardization slows advancement.
Correlation coefficients between dietary intake and plasma or whole blood concentrations are poor (Table 3). This explains inconsistency of dietary intake in assessing health effects of omega-3s. A statistically significant correlation, r > 0.8, was found between plasma and whole blood fatty acid concentrations (Fig 1c). Very hopeful. More effort is needed by researchers and health agencies to identify a common standard for reporting omega-3, omega-6, and all other fatty acids in biological tissues.
Biltoft-Jensen A, Damsgaard CT, Andersen R, Ygil KH, Andersen EW, Ege M, Christensen T, Sorensen LB, Stark KD, Tetens I, Thosen A-V. Accuracy of self-reported intake of signature foods in a school meal intervention study: comparison between control and intervention period. 2015 Br J Nutr doi; 10.1017/S0007114515002020
Mozaffarian D, Ludwig DS. Why is the federal government afraid of fat? The New York Times. The Opinion Pages. July 9, 2015
Trends in intake of energy and macronutrients – United States, 1971-2000. 2004 MMWR 53(04):80-82
Innis SM. Fatty acids and early human development. 2007 Early Human Development doi: 10.1016/j.earlhumdev.2007.09.004
Lewis MD. Severe head trauma and omega-3 fatty acids. 2015 Diet Nutr Crit Care doi: 10.1007/978-4614-7836-2_114
Harris WS, von Schacky C. The Omega-3 index: a new risk factor for death from coronary heart disease. 2004 Prev Med doi: 10.1016/j.ypmed.2004.02.030
Roy S, Brasky TM, Belury MA, Krishnan S, Cole RM, Marian C, Yee LD, Llanos AA, Freudenheim JL, Shields PG. Associations of erythrocyte ω-3 fatty acids with biomarkers of ω-3 fatty acids and inflammation in breast tissue. 2015 Int J Cancer doi: 10.1002/ijc.29675
Abdelmagid SA, Clarke SE, Nielsen DE, Badawi A, El-Sohemy A, Mutch DM, Ma DWL. Comprehensive profiling of plasma fatty acid concentrations in young health Canadian adults. 2015 PLoSONE doi; 10.1371/journal.pone.0116195
Baylin A, Kim MK, Donovan-Palmer A, Siles X, Dougherty L, Tocco P, Campos H. Fasting whole blood as a biomarker of essential fatty acid intake in epidemiologic studies: comparison with adipose and plasma. 2014. Am J Epidemiol doi: 10.1093/aje/kwi213