A new study suggests that choosing a fat-free dressing for your salad may not be the healthiest option after all.

While vinaigrettes may be the better option when it comes to reducing caloric intake, researchers from Purdue University in the US state of Indiana have found that lighter dressings may limit the health benefits of vitamins and nutrients from the salad, particularly carotenoids.

Plant-based carotenoids have been shown to reduce the risk of chronic illnesses like cancer and cardiovascular disease and act as antioxidants.

The reason? A dressing's fat content.

"Overall, 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," said co-author Mario Ferruzzi in a statement.

For their 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 corn oil with polyunsaturated fats.

What they found was that the absorption rate of carotenoids was most dependent on the fat content of the dressing, particularly with the polyunsaturated sauce: the more fat on the salad, the more carotenoids subjects absorbed.

If you want to maximise the health benefits and vitamin absorption of your veggies, scientists suggest opting for canola and olive oil-based dressings which allowed participants to absorb carotenoids at both low and high fat levels.

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