SDA Soybeans: A New Sustainable Source of Omega-3 Fatty Acids
Health authorities have recognized that diets should contain a sufficient amount of omega-3 fatty acids for protection from heart disease.1-2 The American Heart Association has recommended increased fish consumption to boost the currently low intake of the healthful long chain omega-3 fatty acids EPA and DHA;2 however, daily consumption of fish and fish oil is not viewed as a sustainable long term source of omega-3 fatty acids3 and current availability and cost of these foods make them prohibitive to many segments of the population. There is a need for a land-based, sustainable source of omega-3 fatty acids that can be used in a wider range of foods to fit specific dietary habits and budgetary limitations.
Soybeans, canola and flax contain the omega-3 ALA; however, there is insufficient evidence to conclude that ALA promotes heart health than there is for the longer-chain omega-3 fatty acids.4 Furthermore, the fraction of ALA converted to EPA by humans ranges from only 0.2%5 to 7%,6 making ALA an inefficient precursor to the long chain omega-3 fatty acids.
Stearidonic acid (SDA, 18:4) is the omega-3 fatty acid produced by desaturation of ALA along the metabolic path to EPA and DHA in humans. SDA occurs in the food supply today (e.g., in some fish7 and plant oils8), but at relatively low levels when compared to ALA or EPA. Because SDA bypasses the rate-limiting step in the conversion of ALA to EPA and DHA, it is likely to produce more EPA in the body when consumed. Conventional soybean oil contains approximately 7% ALA, but soybeans lack the desaturation enzyme needed to make SDA, EPA or DHA. Through modern biotechnology, the gene for this enzyme has been successfully introduced, resulting in a soybean that produces oil containing ~20% SDA. The new soybean is expected to be commercially available within the next five years. Because of the broad use of soybean ingredients in the food supply, SDA soy-derived ingredients would make it possible to create many different omega-3 enriched foods.
James et al.9 conducted a study to determine the ability of ALA and SDA to increase red blood cell (RBC) concentrations of EPA and DHA in healthy human subjects. The study showed that to increase the RBC levels of EPA by the same amount as 1× EPA, it took about 14× ALA but only about 3× SDA. These results were confirmed in dogs.10 SDA as a component of various oils, including Echium oil, has been fed in other clinical studies, and enrichment of mononuclear cells and lipid fractions in EPA was also noted.11-13 As expected from current understanding of the metabolic pathway, empirical evidence from these clinical and animal studies supports the conclusion that consumption of SDA leads to tissue enrichment of EPA.
Most clinical studies that provide strong evidence for reduced risk of death from cardiovascular disease have used fish or fish oil, which contain a mixture of EPA and DHA, therefore, it is not presently clear whether EPA or DHA is superior in this regard.14 The Japan EPA Lipid Intervention Study, however, provided strong evidence for cardioprotective effects of EPA alone.15 In this trial, over 18,000 hypercholesterolemic patients, all taking low dose statins, were randomized to 1.8 g of EPA ethyl ester or usual care and were monitored for 4.5 years. There was a 19% reduction in the incidence of major adverse cardiac events observed in the EPA group (p=0.01).15 This finding underscores the importance of EPA and supports the rationale that SDA could be an important nutritional product because SDA converts to EPA significantly more efficiently than ALA as demonstrated in RBCs.9 The enrichment of RBCs with EPA and DHA has been shown to reflect cardiac membrane omega-3 fatty acid content. Expressed as a percentage of total fatty acids, this “Omega-3 Index” has been found to highly correlate with reduced risk of cardiovascular disease, particularly sudden cardiac death.16 These data combined with recommendations by health authorities to increase long chain omega-3 consumption support the nutritional value of SDA.
In summary, leading health authorities have concluded that omega-3 fatty acids are important for human health. Limitations of a sustainable supply of fish coupled with a high cost make fish oil an insufficient source of omega-3 fatty acids to the majority of the world’s population. SDA soybean oil produced through biotechnology offers one potential sustainable solution to providing the health benefits of omega-3 fatty acids in foods acceptable to consumers with reasonable shelf life.
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