From Truth in Olive Oil

Mary Flynn, PhD, RD, is Associate Professor of Clinical Medicine at Brown University’s Alpert Medical School in Providence, Rhode Island.  In her first contribution to Truth in Olive Oil, she covered some basic facts of olive oil health, and explained how she came to know, and then love, extra virgin olive oil for its health and nutritional properties.  Here she shares some vital advice about cooking with extra virgin olive oil, based on her several decades of oil-related research and clinical trials.  She also explodes some common olive oil myths, including the bizarre but persistent "don't cook with extra virgin olive oil" fallacy, and offers 3 of her olive oil-based recipes.  Each month, Mary will donate another recipe to Truth in Olive Oil.

Eating and cooking with olive oil

I started to develop my plant-based olive oil diet in 2000, primarily including foods that would improve health and control weight.  I saw extra virgin olive oil as a central part of this diet for several reasons.  I knew it would improve health, but I also thought that using olive oil might increase vegetable intake – another key to good health – since it makes vegetables taste so much better.  Also, I believed that using olive oil at meals would help people to eat less, because including fat in a meal makes the meal more satisfying and delays the onset of hunger after the meal.  All fats do this, but olive oil is the best choice because it's a very healthy fat.

Extra virgin olive oil is the juice of the olive fruit.  Like most unprocessed plant products, it contains a range of health-promoting phytonutrients.  The phytonutrients in olive oil have been shown to decrease the oxidation of LDL (1) (which would lower heart disease risk) and DNA (2) (which would lower cancer risk).  Other phytonutrients in olive oil have been shown to decrease blood levels of glucose and insulin (3); decrease blood pressure (4, 5); decrease blood coagulation (6); and decrease inflammation (7).  This makes extra virgin olive oil very different from seed oils, like soybean, safflower, corn, and canola oil, which have undergone a refining process that destroys phytonutrients.  Refined olive oil, typically labeled “olive oil” in stores, also lacks phytonutrients.  (Take-away point:  buy only extra virgin olive oil!)

I recommend the use of at least 3 tablespoons (45 ml) of extra virgin olive oil per day, most of which you’ll use to cook vegetables.  In the studies cited previously, the health benefits of extra virgin olive oil consumption started at about 2 tablespoons a day, so using 3 tablespoons will ensure that you get these health benefits, and will likely increase your vegetable intake as well.  The use of olive oil to prepare vegetables greatly improves the taste of vegetables, particularly those that are naturally bitter, like many leafy greens, or those that contain sulfur (the brassica family – broccoli, Brussel sprouts, cabbage, cauliflower, kale).  I recommend 1 tablespoon of olive oil per cup of vegetables.  In addition, brassica vegetables contain a phytonutrient family (glucosinolate) that has been shown to be cancer protective (8), but it is water soluble (9), so boiling or steaming these vegetables means you will not get the health benefits from this phytonutrient, since it will be lost in the cooking water.  Cooking the brassica family in extra virgin olive oil therefore means that you get both the health benefits of olive oil itself and of the cancer-fighting phytonutrients in the vegetables.  Plus using olive oil will make them taste so much better than boiling or steaming!

In the 12 years that I’ve employ my diet in my work, I have found, just as I’d hoped, that when my patients and study participants use more olive oil, they consume more vegetables (10, 11), a big plus for health.  In addition, when they report using more than 3 tablespoons of olive oil a day – for example when summer vegetables are plentiful – they are still losing weight.  I would guess there is some upper limit to how much you extra virgin olive oil you can consume before you start gaining weight, but I haven’t yet found it.  In fact, I tell patients that they can never eat too much extra virgin olive oil.  Sure, it’s a fat, but the benefits of extra virgin olive oil clearly outweigh its drawbacks – olive oil will improve your health.

Olive oil and vegetables

Vegetables, like olive oil, have long been associated with improved health.  However, studies looking at the consumption of vegetables do not consistently show decreases in chronic diseases.  There are at least as many studies showing no benefit as those indicating some disease protection from frequent consumption of vegetables.  I believe this inconsistency may be attributable to the type of vegetable consumed in the studies, and to the way the vegetables are prepared.  Certain plant products are clearly more health-protective than others, due to the phytonutrients they contain.  Some of the healthiest, vegetables, which I recommend to my patients, include:  all the brassica family – broccoli, Brussel sprouts, cabbage, cauliflower, kale; any vegetable with deep color, like carrots, peppers, winter squash; and anything leafy and green – spinach, collard greens, etc.  I also recommend the use of frozen vegetables; in fact, I prefer them nutritionally over fresh as in many cases they are kept on the plant longer than what one would buy in a grocery store, so their phytonutrient is likely higher and they have the same vitamin content as store-bought fresh vegetables.

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