Salads are packed with healthy vegetables, but without the right type and amount of salad dressing you could be missing out on several disease-fighting vitamins and nutrients, according to researchers at Purdue University. The study is published online in the Journal Molecular Nutrition & Food Research.

Vegetables are loaded with fat-soluble carotenoids - compounds, such as lutein, beta-carotene, lycopene, and zeaxanthin. Carotenoids are associated with a lower risk of developing diseases, such as heart disease, cancer, and macular degeneration.

The researchers fed 29 study participants salads with different types of dressings in order to determine which kinds and amounts increased carotenoid levels in the bloodstream.

The team compared 3 different dressings:
  • butter-based dressings (as a saturated fat)
  • canola oil-based dressings (as a monounsaturated fat)
  • corn oil-based dressings (as a polyunsaturated fat)
Each salad was served with either 3 grams, 8 grams or 20 grams of fat from dressing.

Monosunsaturated fat dressings need less fat for optimum carotenoid absorption

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

Lead author, Mario Ferruzzi, a Purdue associate professor of food science, explained:

"If you want to utilize more from your fruits and vegetables, you have to pair them correctly with fat-based dressings. 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."

They found that with both corn oil and butter, higher amounts of fat in the dressing led to better absorption of carotenoids. However, canola and olive oil-based dressings led to the same absorption of carotenoids at 3 grams of fat as it did 20 grams.

The findings indicate that dressings with monounsaturated fat may be a good choice for individuals' craving lower fat options, but still wanting to optimize absorption of health-promoting carotenoids from fresh vegetables.

Ferruzzi explained:

"Even at the lower fat level, you can absorb a significant amount of carotenoids with monounsaturated fat-rich canola oil. 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."


Thousand-Island-Dressing (Salad)
Lipids (fats) in salad dressings enhance carotenoid absorption


Ferruzzi and team's next project is to determine how meal patterning impacts nutrient absorption. Their goal is to find out whether people absorb more nutrients if they consume vegetables at one sitting, or by eating them throughout the day.

Written by Grace Rattue