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June 20, 2012 | Dress salads with canola or olive oil to get most nutrients out of veggies |
Washington: The vegetables in salads are packed with important vitamins and nutrients, but
you won’t get much benefit without the right type and amount of salad dressing,
according to a Purdue University study. In a human trial, researchers fed subjects
salads topped off with saturated, monounsaturated and polyunsaturated fat-based
dressings and tested their blood for absorption of fat-soluble carotenoids – compounds
such as lutein, lycopene, beta-carotene and zeaxanthin. Those carotenoids are
associated with reduced risk of several chronic and degenerative diseases such
as cancer, cardiovascular disease and macular degeneration. The study found that
monounsaturated fat-rich dressings required the least amount of fat to get the
most carotenoid absorption, while saturated fat and polyunsaturated fat dressings
required higher amounts of fat to get the same benefit. “If you want to utilize
more from your fruits and vegetables, you have to pair them correctly with fat-based
dressings,” said Mario Ferruzzi, the study’s lead author and a Purdue associate
professor of food science. “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,”
Ferruzzi stated. In the test, 29 people were fed salads dressed with butter as
a saturated fat, canola oil as a monounsaturated fat and corn oil as a polyunsaturated
fat. Each salad was served with 3 grams, 8 grams or 20 grams of fat from dressing.
The soybean oil rich in polyunsaturated fat was the most dependent on dose. The
more fat on the salad, the more carotenoids the subjects absorbed. The saturated
fat butter was also dose-dependent, but to a lesser extent. Monounsaturated fat-rich
dressings, such as canola and olive oil-based dressings, promoted the equivalent
carotenoid absorption at 3 grams of fat as it did 20 grams, suggesting that this
lipid source may be a good choice for those craving lower fat options but still
wanting to optimize absorption of health-promoting carotenoids from fresh vegetables.
“Even at the lower fat level, you can absorb a significant amount of carotenoids
with monounsaturated fat-rich canola oil,” Ferruzzi said. “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,” he explained. The findings
were build on a 2004 Iowa State University study that determined carotenoids were
more bioavailable – absorbed by the intestines – when paired with full-fat dressing
as opposed to low-fat or fat-free versions. The study was published early online
in the journal Molecular Nutrition and Food Research.
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