Fat-free Salad Dressing Limits Health Benefits of Vegetables

By Chelsea Whyte on June 20, 2012 6:45 PM EDT

salad
A little fat in salad dressing goes a long way toward helping your body absorb nutrients from vegetables. (Photo: Creative Commons)

The common parent's directive to "Eat your veggies!" may need an amendment. A human trial designed by food scientists at Purdue University found that many of the nutrients found in salad vegetables cannot be absorbed by your body without some fat.

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

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The researchers fed subjects salads topped with dressings based on three types of fats: saturated (butter), monounsaturated (canola oil), and polyunsaturated (corn oil). They then tested their blood to measure absorption levels of fat-soluble carotenoids, such as lutein, lycopene, beta-carotene and zeaxanthin.

Carotenoids, found in high numbers in colorful vegetables like carrots, tomatoes and onions, are associated with a reduction in cancer risk, protection of eyesight and a lower risk of cardiovascular-related death. One study even found that they can make you appear more beautiful, reports the Huffington Post.

Over three days, 29 people were served salads with 3 grams, 8 grams, or 20 grams of fat from dressing. They found that dressings with polyunsaturated fats, like soybean oil or corn oil, were dose-dependent, meaning the more fat on the salad, the more carotenoids were absorbed into the blood stream. Butter-rich dressings, or any with saturated fats, were also dose-dependent, but to a lesser degree.

But that doesn't mean you need to consume a lot of fat to get the nutrition you need you're your veggies. The study showed that monounsaturated fat-rich dressings helped absorb the same amount of nutrients whether there were 3 or 20 grams of fat on the plate, which means you can get away with less fat on the salad while still leeching a good amount of carotenoids from vegetables into the body. For people looking to keep the calorie count low and still get the benefit of nutrients from salad, the best options are canola- or olive oil-based dressings.

"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."

The findings 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, reports Futurity.org

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