Beware McDougall and Esselstyn followers. Those who choose no-fat or low-fat dressings for vegetables or salads may miss out on a significant amount of vitamins and nutrients, say U.S. researchers.

Lead author Mario Ferruzzi, a Purdue University associate professor of food science, and colleagues fed subjects salads topped off with saturated, monounsaturated and polyunsaturated fat-based dressings and tested their blood for absorption of fat-soluble carotenoids -- beneficial compounds such as lutein, lycopene, beta-carotene and zeaxanthin.

The carotenoids are associated with reduced risk of several chronic and degenerative diseases such as cancer, cardiovascular disease and macular degeneration, an eye disease that causes blindness, Ferruzzi said.

In the study, 29 people were fed salads dressed with butter as a saturated fat, canola oil as a monounsaturated fat and corn oil as a polyunsaturated fat. Each salad was served with 3 grams, 8 grams or 20 grams of fat from dressing.

The study, published online in the journal Molecular Nutrition & Food Research, found monounsaturated fat-rich dressings required the least amount of fat to get the most carotenoid absorption, while saturated fat and polyunsaturated fat dressings required higher amounts of fat to get the same benefit.

The soybean oil rich in polyunsaturated fat was the most dependent on dose -- the more fat on the salad, the more carotenoids the subjects absorbed. The saturated fat butter was also dose-dependent, but to a lesser extent, the study said.

Monounsaturated fat-rich dressings, such as canola and olive oil-based dressings, promoted the equivalent carotenoid absorption at 3 grams of fat as it did 20 grams, suggesting the lipid source may be a good choice for those craving lower fat options but still wanting to optimize carotenoids, Ferruzzi said.

I personally use extra virgin olive oil on my salads, and I also drizzle it on some steamed vegetables, such as yellow crrookneck squash and any kind of green bean. There is no foundation to bashing extra virgin olive oil. All of the research shows that it's good.