A new study shows that choosing a low-fat dressing for your salad might help you keep your weight down because it has fewer calories, but you could lose some other health benefits.

The study found higher-fat dressings help the body absorb more carotenoids, compounds in vegetables linked with a reduced risk of illnesses including cancer and heart disease.

Researchers from Iowa State University fed 29 people salads dressed with butter, high in saturated fat, canola oil for monounsaturated fat, and corn oil for polyunsaturated fat.

Each salad was dished up with 3 grams, 8 grams or 20 grams of fat from dressings to see if fat dosage made a difference to the overall results.

The participants had their blood tested for absorption of fat-soluble carotenoids, which are compounds associated with a reduced risk of several chronic and degenerative diseases such as cancer and cardiovascular disease.

The study found higher-fat dressings help the body absorb more carotenoids, compounds in vegetables linked with a reduced risk of illnesses including cancer and heart disease

With all but the canola oil, made from genetically modified rapeseed, the more fat that was used the more carotenoids were absorbed, says the study in the journal Molecular Nutrition & Food Research.

Canola oil promoted the same carotenoid absorption with three grams of fat as with 20 g, suggesting it may be a healthy choice for weight watchers. Olive oil is also rich in monounsaturated fat.

Professor Mario Ferruzzi of Purdue University said: “If you want to utilise 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.”

Results showed corn oil was the most dependent on dose, with the more fat on the salad, the more carotenoids the participants absorbed.

The butter rich in saturated fat was also dependent on dose when drizzled on the salads, but not to a lesser extent.

Canola oil and olive-oil based dressings promoted the same carotenoid absorption at three grams of fat, as they did at 20 grams – suggesting this would be a good choice of dressing for people watching their weight but wanting to remain healthy.

The researchers are taking the study further by trying to understand how meal patterns affect nutrient absorption – determining whether people absorb more nutrients if they eat vegetables at one time or spread throughout the day.

Prof. Mario Ferruzzi added: “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.”