Your friend is right. Results of a small study published in the August 2004 issue of the American Journal of Clinical Nutrition showed that our bodies don't absorb such important protective antioxidants as beta-carotene, alpha-carotene or lycopene from vegetables unless we eat them accompanied by some fat. That doesn't mean dousing your salad with gobs of ranch dressing. Adding a little cheese or a dressing made with extra-virgin olive oil is all you need to absorb the vital nutrients vegetables contain.
For the study, researchers at Iowa State University recruited seven people to eat three different salads on three separate occasions. All the salads contained spinach, romaine lettuce, cherry tomatoes and carrots. When the volunteers used non-fat dressings on their salads, they didn't absorb any of the alpha-carotene, beta-carotene or lycopene (the red pigment in tomatoes that helps prevent prostate cancer) that the vegetables contained. However, when they used a reduced-fat dressing containing six grams of fat, levels of carotenoids in their bodies went up; when they ate full-fat dressings (containing 28 grams of fat), the carotenoid levels increased even more.
The researchers noted that they're not sure their findings apply to cooked vegetables. However, we do know that lycopene is much more available to the body from cooked tomatoes than from raw ones. And since it is fat-soluble, you need to eat your cooked tomatoes with some fat (preferably extra-virgin olive oil) to facilitate absorption. My favorite way to do this is to make a marinara sauce with good olive oil. I cook up a big pot of it, use some right away, and freeze the rest.
I recommend that 30 percent of your daily calories come from fat with an emphasis on the healthy monounsaturated fat found in olive oil, nuts and avocados as well as omega-3 fatty acids in salmon, sardines, walnuts and flaxseeds. By all means use an olive oil-based dressing on your salads - you'll enjoy them more and get more nutrients as well.
Andrew Weil, M.D.