MINNESOTA, MINNEAPOLIS. Blood levels of fatty acids are believed to reflect the dietary intake of fatty acids. Researchers at the University of Minnesota now report that while high fat diets tend to increase the level of omega-6 acids (generally undesirable) low fat diets tend to increase the level of beneficial omega-3 acids such as EPA and DHA (eicosapentaenoic acid and docosahexaenoic acid, respectfully).
Their clinical trial involved 10 healthy subjects who were randomized to receive a high fat diet (45% fat) for a 28-day period or a low fat diet (20% fat) for the same period. After a 3-4 week washout period the participants were fed the other diet for an additional 28 days. Blood samples were taken at the beginning and end of each feeding period. The two diets provided the same amount of calories (isoenergic) and had equivalent proportions of the different fatty acids notably linoleic and linolenic acids. The researchers noted that the high fat diet produced a significant increase in the proportion of omega-6 fatty acids, particularly the long chain ones, in the phospholipids and cholesterol fractions of the blood. In contrast, the low fat diet produced a significant increase in the proportion of omega-3 fatty acids, particularly EPA and DHA, in the phospholipids and cholesterol fractions and also resulted in a lower overall omega-6 content in these fractions.
The researchers speculate that the benefits of a low fat diet may, in part, be due to the higher blood levels (phospholipids and cholesterol fractions) of beneficial omega-3 fatty acids (especially EPA and DHA) engendered by a low fat diet.
Raatz, Susan K., et al. Total fat intake modifies plasma fatty acid composition in humans. Journal of Nutrition, Vol. 131, February 2001, pp. 231-34