A recent study (Shellen etal., 2012) published in the journal Molecular Nutrition & Food Research has investigated how salad dressings aid absorption of fat-soluble carotenoids (such as lutein, beta-carotene, lycopene, and zeaxanthin) from the salad ingredients. Carotenoids are associated with a lower risk of developing diseases, such as heart disease, cancer, and macular degeneration.

29 study participants ate salads with different types of dressings in order to determine which kinds and amounts increased  carotenoid levels in the bloodstream. They discovered that dressings rich in monounsaturated fat required the least amount of fat to get the most carotenoid absorption. Dressings rich in saturated and polyunsaturated fat required higher amounts of
fat to produce the same benefit. Fat-free dressings do not enhance carotenoid absorption.

Mono-unsaturated oils such as an olive oil-based dressing led to the same absorption of carotenoids at 3 grams of fat as did 20 grams of saturated butter-based or polyunsaturated corn oil-based dressings.

 

References

Shellen R. Goltz, Wayne W. Campbell, Chureeporn Chitchumroonchokchai, Mark L. Failla and Mario G. Ferruzzi (2012) “Meal
triacylglycerol profile modulates postprandial absorption of carotenoids in humans” Molecular Nutrition & Food Research. 56(6), 866–877