The health benefits of the Mediterranean diet were initially realized by studying people who ate this diet for generations. The diet is plant-based and includes daily generous servings of extra virgin olive oil at multiple meals. It is clearly not a low-fat diet. Health officials in the US acknowledged the health benefits of a Mediterranean diet decades ago, including the health benefits of extra virgin olive oil. I remember reading editorials in the 1980’s that discussed the health benefits of extra virgin olive oil, but the editorials mistakenly concluded that Americans do not want oil that has a taste so it was thought that Americans would not embrace extra virgin olive oil. Health officials in the US also mistakenly concluded that the health benefits of extra virgin olive oil were due to the high monounsaturated fat content. Hence the development of canola oil, made from the rapeseed plant with the name “canola” coming from the trademark name of the “Rapeseed Association of Canada”. Canola oil has minimal taste and it is reasonably high in monounsaturated fat (62%), but not as high as olive oil (77%).
The idea that the monounsaturated fat content is responsible for the health benefits lead to the development of the Med diet score. (1) The Med diet score gives points to foods of a traditional Mediterranean diet that have been shown to have health benefits like vegetables, fruits, legumes, nuts, and cereals and subtracts points for foods that are unhealthy, like meat and meat products and dairy. Interestingly, for examining the impact of dietary fat, the Med diet score uses the ratio of monounsaturated fat (MFA) to saturated fat (SFA) in the diet being examined, not the extra virgin olive oil content of the diet. If the populations that are being studied are in one of the Mediterranean countries, the MFA: SFA would likely be assessing at least some extra virgin olive oil. However, when the Med diet score is used to assess health, especially outside Mediterranean countries, the data should be examined with caution as you would need to know what foods are supplying the monounsaturated fat. For example in the US, the major source of monounsaturated fat until about 2004 was meat. (2) In 2005 “salad cooking oils” caught up with meat, supplying 23.9 % of the monounsaturated fat in the US diet to 21.4% from meat. While olive oil consumption has increased in the US, in 2005 soybean oil represented close to 80 % of the salad oils consumed in the US. (3) Since that time the soybean oil contribution has decreased with increases mainly in canola and palm oil. (3) However, in 2010 (the last year data is available from the USDA) meat still supplied 21.5% of the monounsaturated fats content of the US diet to 32.3% from salad cooking oils. So a study using the Med diet score to assess health in the US likely has a better chance of finding no benefit, and possibly harm, due to a large proportion of the food source of mono-unsaturated fat could be meat or canola oil.
It is important to note the health and taste attributes of extra virgin olive oil are largely due to the bio-active plant compounds it contains, including phenols. Other grades of olive oil, including “olive oil” and “refined olive oil” undergo refining processes that remove most of the phenols. While the MFA content remains essentially the same, the number of bioactive compounds and phenols are mostly lost. Extra virgin olive oil has been related to decreasing the risk of a range of chronic diseases and improv-ing numerous risk factors for chronic diseases. Extra virgin olive oil has been shown to improve blood pressure (4-6) insulin sensitivity, (7) blood levels of glucose and insulin, (7-10) levels of HDL (11-16) and HDL
function (17,18) and to decrease oxidation (19,20), including decreasing the oxidation of LDL. (5,11,12,14,16,21,22) No other food has the range and magnitude of the health benefits of extra virgin olive oil. If the health benefits of extra virgin olive oil were due to the monounsaturated fat content, all studies using olive oil would have the same health benefits, and they do not. In addition, canola oil would show health benefits, and it does not. (23) The health benefits of extra virgin olive oil are clearly due to the phenols found in extra virgin olive oil as studies assessing the benefits for varying amounts of total phenols show better benefits with higher phenol content (approximately greater than 200 mg/kg) and no benefit with low (< 50 mg/kg) phenol content, a level that would not qualify as extra virgin. (5,12,14,16,17,21)
The traditional Mediterranean diet included extra virgin olive oil out of necessity – it was the only oil option in the area. The fact that it is delicious and has numerous health benefits is indeed a fortuitous bonus. It is possible to see some health benefits from the Med diet score due to the foods receiving a positive score -vegetables, fruits, nuts, legumes- that could contribute to health. However, if the MFA:SFA value is used to assess the contribution from dietary fat outside of the Mediterranean countries, the results should be interpreted with caution.
References
1. Trichopoulou A, Kouris-Blazos A, Wahlqvist ML, et al. Diet and overall survival in elderly people. Bmj 1995;311:1457-60.
2. Nutrient Content of the U.S. Food Supply, 1909-2010. 2010. 2019, at www.cnpp.usda.gov/USFoodSupply-1909-2010.) Accessed February 16, 2019.
3. Trends in U.S. Edible Oil Consumption and the High Oleic Soybean Oil Opportunity: United Soybean Board; 2017.
4. Ferrara LA, Raimondi AS, d’Episcopo L, Guida L, Dello Russo A, Marotta T. Olive oil and reduced need for antihypertensive medications. Arch Intern Med 2000;160:837-42.
5. Moreno-Luna R, Munoz-Hernandez R, Miranda ML, et al. Olive oil polyphenols decrease blood pressure and improve endothelial function in young women with mild hypertension. Am J Hypertens;25:1299-304.
6. Perona JS, Canizares J, Montero E, Sanchez-Dominguez JM, Catala A, Ruiz-Gutierrez V. Virgin olive oil reduces blood pressure in hypertensive elderly subjects. Clin Nutr 2004;23:1113-21.
7. Ryan M, McInerney D, Owens D, Collins P, Johnson A, Tomkin GH. Diabetes and the Mediterranean diet: a beneficial effect of oleic acid on insulin sensitivity, adipocyte glucose transport and endothelium-dependent vasoreactivity. Qjm 2000;93:85-91.
8. Farnetti S, Malandrino N, Luciani D, Gasbarrini G, Capristo E. Food fried in extra-virgin olive oil improves postprandial insulin response in obese, insulin-resistant women. J Med Food;14:316-21.
9. Loued S, Berrougui H, Componova P, Ikhlef S, Helal O, Khalil A. Extra-virgin olive oil consumption reduces the age-related decrease in HDL and paraoxonase 1 anti-inflammatory activities. Br J Nutr;110:1272-84.
10. Madigan C, Ryan M, Owens D, Collins P, Tomkin GH. Dietary unsaturated fatty acids in type 2 diabetes: higher levels of postprandial lipoprotein on a linoleic acid-rich sunflower oil diet compared with an oleic acid-rich olive oil diet. Diabetes Care 2000;23:1472-7.
11. Cicero AF, Nascetti S, Lopez-Sabater MC, et al. Changes in LDL fatty acid composition as a response to olive oil treatment are inversely related to lipid oxidative damage: The EUROLIVE study. J Am Coll Nutr 2008;27:314-20.
12. Covas MI, Nyyssonen K, Poulsen HE, et al. The effect of polyphenols in olive oil on heart disease risk factors: a randomized trial. Ann Intern Med 2006;145:333-41
