Oleic acid (OA) is an omega-9 fatty acid. In the diet, olive oil is the most common source for OA, though many seeds and grapeseed oil are other OA-rich foods. OA consumption relates to many health benefits, particularly in the realm of cardiovascular health; OA is believed to be one of the most potent health-promoting factors in the Mediterranean diet.6 However, one must be aware also that olive oil, the dietary source of most OA in the diet, contains other components that might also be involve in the beneficial role of olive oil, specifically extra-virgin olive oil (EVOO, as Rachael Ray says) which has a greenish hue in its purest form.7

            As important as the structural (cell membrane incorporation) and precursor (hormone production) roles of these EFAs (including OA as a conditional essential fatty acid) are, one must not lose sight of the fact that these are dietary fats that can be burned as calories or stored as body fat.

            Previous studies have looked closely at the various fatty acids to see if any are more prone to being burned for calories or stored as body fat.8-10 When comparing animal to human studies, there is a fair amount of conflicting data, making it difficult to interpret the findings.10,11 Fortunately, there is a growing body of data in human studies that allows for a more focused interpretation. A recent study used an elegant approach in determining the relative propensity of the EFAs (including OA) to result in fat storage or calorie burning, as well as any effect on the overall metabolism (rate of calorie burning).12 This study, performed by Dr. Peter Jones and his colleagues at McGill University in Canada, compared the metabolic effect (calorie burning) and endpoint of the three EFAs.

            Subjects in this study were healthy, young men who were not elite athletes. They were normal weight and had no abnormalities in screening lab work. The subjects arrived for three different test sessions. Prior to each, subjects fasted for 16 hours and arrived to the metabolic lab in a rested condition. Baseline (prior to receiving the test breakfast) measures were recorded to allow the scientists to measure the change in body temperature, metabolic rate and degree of fat versus carbohydrate oxidation (how much fats were burned as calories in comparison to carbohydrates) following the administration of a test breakfast. The subjects underwent three tests, separated by one week each. On each occasion, a standardized breakfast consisted of a vegetable omelet, fried potatoes, a glass of milk and the test oil poured over an English muffin; the macronutrient ratio was verified as being 60 percent fat, 30 percent carbohydrate and 10 percent protein, providing one-third of the subjects’ assessed daily maintenance calorie needs. The test oils were olive (71.3 percent OA), sunflower (69.7 percent LA) and flaxseed (58.8 percent ALA), given in random order. These oils were chosen because they are concentrated sources of OA, LA and ALA respectively.