Climate-based variability in the essential fatty acid composition of soybean oil

Background: Soybean oil is a major dietary source of the essential fatty acids linoleic acid (LA) and alpha-linolenic acid (ALA); however, high-daytime temperatures during seed development reduce desaturase activity in soybeans. The resultant reduction in LA and ALA levels is a phenomenon well-known to soybean breeders, although the impact of this interaction between plants and environment on human nutrition is poorly understood. Objectives: Using data from the literature, we developed a model for soybean essential fatty acid composition. Combining this model with contemporary agricultural and meteorological data sets, we determined whether insufficiency of essential fatty acids could result from geographic, intrayear, or interyear variability. Methods: We modeled this change using 233 data points from 16 studies that provided fatty acid composition data from plants grown under daytime high temperatures ranging from 15 degrees C to 40 degrees C. Results: As temperature increased, LA and ALA concentrations decreased from 55% to 30% and 13% to 3.5%, respectively. Application of the model to daytime high temperatures from 2 growth periods over 6 y showed significant regional, interyear, and intrayear variation in essential fatty acid content (P < 0.05). Using county yield data, we developed oil fatty acid models for the 3 top-producing regions of the United States. From this work, it was determined that soybean oil manufactured from soybeans in the southern United States may contain insufficient ALA to meet human nutritional needs because of high-daytime temperatures. Conclusions: This work suggests that climate-based variation may result in many human populations not achieving an adequate daily intake of ALA.