Featured article in the Winter 2015 Issue of Nutrition Close-Up; written by James D. House, PhD
The Food and Nutrition Board of the Institute of Medicine published in 2002 official estimates of the human requirements for fatty acids.1 At that time, only two fatty acids, the major constituents of fats and oils, were deemed to be essential for the healthy, adult human population: linoleic acid (18:2n-6), an omega-6 fatty acid; and ?-linolenic acid (18:3n-3), an omega-3 fatty acid. These fatty acids are considered essential because they cannot be synthesized by the body, and must therefore be supplied through the diet. Linoleic acid, a polyunsaturated fatty acid, is found in most dietary fats and oils, and is particularly high in corn and soybean oils. ?-linolenic acid (ALA) is less prevalent in the diet, with potential sources including flaxseed and flax oil, hemp oil and canola oil, as well as certain animal products, including eggs (Table 1). With respect to requirement estimates, the current Adequate Intake (AI) values for linoleic acid are 12 and 17 g/d for young women and men, respectively. The Adequate Intake values for ALA are 1.1 and 1.6 g/d for young women and men, respectively.
With respect to ALA, dietary modeling exercises using NHANES data have estimated intakes of 1.5 g/d for adults,2 thus providing evidence that the AI for this fatty acid is being met. However, arguments are being put forward to revise our current thinking in relation to fatty acid requirements. Specifically, questions are being posed as to whether Dietary Reference Intake (DRI) values should be established for the long chain polyunsaturated fatty acids (LCPUFA) that are derived from ALA.3 While the body can convert ALA to eicosapentaenoic acid (EPA, 20:5n-3) and later to docosahexaenoic acid (DHA, 22:6n-3), the conversion of ALA to these omega-3 LCPUFA is inefficient, with some estimates of the conversion of ALA to DHA being less than 0.5%.4 As EPA and DHA are integral to normal cell growth and development, and for optimal neural, visual and cognitive function, dietary sources of the long chain n-3 PUFA are important. Recent calls to establish DRI values for EPA and DHA have been primarily framed around the available evidence linking their consumption to reduced risk of cardiovascular disease.3 The 2010 Dietary Guidelines for Americans recommends the consumption of 3.5 oz (100 g) of seafood per week in order to ingest, on average, approximately 250 mg of EPA +DPA per day.5 Other groups, including the American Heart Association, have advocated higher intakes (>500 mg EPA + DHA per day)6 for healthy adults, with the intake coming primarily from fatty fish. Current estimates of EPA + DHA intake indicate that Americans are consuming significantly less than 250 mg/d, with some estimates being below 100 mg/d.7
Given the recommendations of certain authorities, coupled with evidence of low habitual intake from seafood, additional opportunities to provide the omega-3 LCPUFA to the population should be considered. These opportunities could include:
1. Creating greater awareness of the need to consume fatty fish
2. Using supplements
3. Selection and breeding (Traditional or via genetic modification) of plants with oils high in omega-3 fatty acids or the precursor fatty acid stearidionic acid, or
4. Using fortified foods
With respect to the latter opportunity, enhancing foods with marine oils is feasible, yet requires strict attention to the resultant sensory attributes of the final food product. The use of microencapsulated oils can achieve this goal. Alternatively, the enrichment of animal products with DHA + EPA is attainable, and the egg is particularly amenable to modification. Laying hens are capable of efficiently converting ALA from plant-based ingredients, such as flaxseed, into the omega-3 LC-PUFA.8 Furthermore, hens are efficient at depositing pre-formed dietary DHA, either from fish or algal sources, into the egg, and these feeding regimens tend to give higher final DHA levels in the egg.9 Depending on the chicken feeding regimen employed, one omega 3-enriched egg can contain upwards of 400 mg of total omega-3 fatty acids, with 150-200 mg of EPA + DHA, thus providing consumers a choice between conventional and omega-3 eggs.10
Returning to the central question as to whether we are consuming sufficient omega-3 fatty acids, a qualified response is best at this stage. Based on available evidence, ALA intakes are in agreement with current guidelines; however, intake of the omega-3 LCPUFA (EPA and DHA) is not in keeping with guidelines established by national and international bodies. The latter does not include the DRI estimates, and future expert panels will need to be convened in order to weigh the available evidence in support of an Adequate Intake value for the omega-3 LCPUFAs.
James D. House, PhD, is Professor and Head of the Department of Nutritional Sciences at the University of Manitoba in Winnipeg, Canada. Dr. House is studying the relationship between water soluble vitamin nutrition, the metabolism of amino acids, and how they relate to optimal growth and health of individuals. He also maintains a strong focus towards the development of functional foods of animal origin, including eggs with enhanced nutritional value.
References
1. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). National Academies Press, 2002.
2. Johnson GH, Keast DR, Kris-Etherton PM. Dietary modeling shows that the substitution of canola oil for fats commonly used in the United States would increase compliance with dietary recommendations for fatty acids. J Am Diet Assoc. 2007;107:1726-34.
3. Flock MR, Harris WS, Kris-Etherton PM. Long-chain omega-3 fatty acids: Time to establish a dietary reference intake. Nutr Rev. 2013;71:692-707.
4. Plourde M, Cunnane SC. Extremely limited synthesis of long chain polyunsaturates in adults: Implications for their dietary essentiality and use as supplements. Appl Physiol Nutr Metab. 2007;32:619-34.
5. Dietary guidelines for Americans, 2010. Accessed: http://www.health.gov/dietaryguidelines/2010.asp; November 20, 2014.
6. American Heart Association Fish and Omega-3 Fatty acids. Accessed: http://www.heart.org/HEARTORG/ GettingHealthy/NutritionCenter/HealthyEating/Fish-and-Omega-3-Fatty-Acids_UCM_303248_Article.jsp; November 20, 2014.
7. Papanikolaou Y, Brooks J, Reider C, Fulgoni VL 3rd. U.S. adults are not meeting recommended levels for fish and omega-3 fatty acid intake: Results of an analysis using observational data from NHANES 2003- 2008. Nutr J. 2014;13:31.
8. Gakhar N, Goldberg E, Jing M, Gibson R, House JD. Effect of feeding hemp seed and hemp seed oil on laying hen performance and egg yolk fatty acid content: Evidence of their safety and efficacy for laying hen diets. Poult Sci. 2012;91:701-11.
9. Lawlor JB, Gaudette N, Dickson T, House JD. Fatty acid profile and sensory characteristics of table eggs from laying hens fed diets containing microencapsulated fish oil. Anim. Feed Sci. Tech. 2010;156:97-103.
10. Ferrier LK, Caston LJ, Leeson S, Squires J, Weaver BJ, Holub BJ. Alpha-Linolenic acid- and docosahexaenoic acid-enriched eggs from hens fed flaxseed: Influence on blood lipids and platelet phospholipid fatty acids in humans. Am J Clin Nutr. 1995;62:81-6.