Mario Ferruzzi, the lead author of the study and an associate professor of food science at Purdue, said that in order to get more from eating fruits and vegetables, they need to be paired correctly with fat-based dressings. While a salad with fat-free dressing is lower in calories, the absence of fat causes the loss of some of the benefits of eating vegetables.

Researchers also found that some fats are dose dependent. Soybean oil, a polyunsaturated fat, was the most dependent on dose, i.e., the more dressing on the salad, the more carotenoids the subjects absorbed. Butter, a saturated fat, was also dose-dependent but to a lesser degree.

Dressing made with monounsaturated fat, like canola and olive oil, promoted nearly as much absorption of carotenoids at three grams of fat as it did at 20 grams of fat, so these may be the best dressings for people wanting both a low fat dressing and the benefit of health-promoting carotenoids from their salads.

Carotenoids are phytochemicals found in plant foods. They include such compounds as lutein, beta-carotene, and zeaxanthin. Carotenoids give plant foods their color and act as antioxidants in the human body. The body produces free radicals which are harmful compounds during normal metabolism as well as when infection is present. The harmful effect of free radicals is considered a major cause of cancer, cardiovascular disease, immune-system dysfunction, and macular degeneration. The antioxidant properties of phytochemicals stop free radicals from damaging the body. Carotenoids seem to be one of the more important types of phytochemicals

So if you're looking for a reason to quit buying those less-than-tasty fat-free salad dressings, this could be it!

The study was published early online in the journal Molecular Nutrition & Food Research.

This article originally appeared on TheDoctorWillSeeYouNow.com, an Atlantic partner site.

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