If you think you're doing your health a favor by forgoing blue cheese or ranch dressing in favor of vinaigrette on your salad, you may be needlessly depriving yourself.

According to a new study, fat is necessary for your body to process the vitamins and nutrients in vegetables, especially carotenoids, the New York Daily News reports. Carotenoids have been shown to reduce the risk of chronic illnesses such as cancer and cardiovascular disease and to act as antioxidants.

“Pairing with fat matters. You can absorb significant amounts of carotenoids with saturated or polyunsaturated fats at low levels, but you would see more carotenoid absorption as you increase the amounts of those fats on a salad,” study lead author Mario Ferruzzi, a Purdue University associate professor of food science, said in a statement. “If you have a salad with a fat-free dressing, there is a reduction in calories, but you lose some of the benefits of the vegetables.”

For the study, published in the journal Molecular Nutrition & Food Research, scientists fed 29 people salads topped with three types of dressings: a butter-based dressing full of saturated fats; a dressing made with canola oil, or monounsaturated fat; and one made with soybean oil, or polyunsaturated fat. Each salad was otherwise identical, composed of tomatoes, carrots, baby spinach, Romaine lettuce — and the wild card, Chinese wolfberry (it's high in carotenoids and flavonoids). After consumption of the salad, subjects were instructed to wipe their bowls with a piece of white bread to ensure that all of the butter or oil was ingested.

Researchers then measured the subjects' blood for carotenoid absorption. They found that subjects who had eaten the canola oil dressing had the highest levels of carotenoids in their bloodstream. Further, salads made with polyunsaturated soybean oil were the most dose-dependent. The more soybean oil the subjects consumed, the more carotenoids they absorbed. Saturated fat dressings also were dose-dependent, but to a lesser extent. Monounsaturated canola oil dressings, on the other hand, were just right. They promoted the same level of carotenoid absorption with a 3-gram serving as with a 20-gram serving.

If you want to maximize the health benefits and vitamin absorption of your veggies, scientists suggest opting for canola- and olive oil-based dressings.

A 2004 study from Iowa State University also found that people absorb more carotenoids from vegetables when paired with full-fat dressings compared with low-fat or fat-free versions.

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