On my drive in to work on Monday morning, I listened to a story by Allison Aubrey on NPR’s Morning Edition about the benefits of eating olive oil, and that fresh-pressed oil provides the most benefit: http://www.npr.org/blogs/thesalt/2013/09/30/226844915/to-get-the-benefits-of-olive-oil-fresh-may-be-best. Ms. Aubrey referred to a large randomized controlled trial that was published in The New England Journal of Medicine in April 2013 (http://www.nejm.org/doi/full/10.1056/NEJMoa1200303) that found a benefit when people in Spain who were at high risk of heart attacks and strokes added 4 tablespoons of olive oil a day to an already Mediterranean-type diet (that is, a diet high in fruits, vegetables, legumes, nuts, olive oil, and cereals and low in dairy products, red and processed meats, and sweets).
Ms. Aubrey stated in her story, “And what researchers found was that a Mediterranean diet rich in olive oil cut the risk of heart attacks and strokes by 30 percent. The nut group, which was consuming olive oil as well, did well, too.” This is a touch misleading, though — and a classic problem with how journalists interpret and report data from clinical trials to the general public.
What the study actually found was that there was a small decrease in the number of strokes in people who consumed the added amount of olive oil, but that there was NO DIFFERENCE in the number of heart attacks, or in the number of deaths (see Table 3 in the paper for the actual numbers). http://www.nejm.org/doi/full/10.1056/NEJMoa1200303#t=article
But because the study combined all three of these endpoints (stroke, heart attack, and death) into a single endpoint, they have been grouped together by the authors of the study — and by journalists, who are inferring that the olive oil decreased the number of heart attacks and giving this misinterpretation to the public.
This isn’t to say that olive oil doesn’t have benefits. I just believe it’s important that research findings don’t get twisted when they are interpreted by journalists.
I also think we should keep in mind that 4 tablespoons of olive oil is a LOT of oil! Adding that much olive oil to your diet would provide an additional 480 calories a day — and for people trying to watch their total energy intake in order to maintain or lose weight, this can be a significant amount of calories! If you kept your diet and activity levels the same and added 4 tablespoons of olive oil a day, you could pack on a pound of fat every week! So it’s important not to just go out and start sucking down the olive oil from the bottle.
I personally think that the sensible thing to do would be to DECREASE the calories in your diet by decreasing other foods containing saturated fats (like butter; high-fat dairy products like cream, half-and-half, cheese, or ice cream; or red and processed meats like sausage or steaks containing a lot of fat) and simultaneously increase the amount of olive oil in your diet (by cooking with it or using it in place of butter or cream on bread or in sauces and dressings). This could provide the healthy monounsaturated fats and other healthy substances like polyphenols without adding extra calories to your diet: a win-win.