A recent study conducted by Wendy White, associate professor of food science and nutrition at Iowa State University, shows that eating salad vegetables with some added fat promotes the absorption of lycopene, alpha- and beta-carotenes, all of which aid in the fight against cancer and heart disease.
On the flip side, eating a salad completely devoid of fat deprives your body of these beneficial substances. Likewise, you can eat a handful of carrot sticks, but without the accompanying ranch dressing or dip, your body can kiss the beta-carotene goodbye.
"We're certainly not advocating a high-fat diet, or one filled with full-fat salad dressing," White explained. "If you'd like to stick with fat-free dressing, the addition of small amounts of avocado or cheese in a salad may help along the absorption.
"Our findings are actually consistent with U.S. dietary guidelines, which support a diet moderate, rather than very low, in fat," White continued. "But what we found compelling was that some of our more popular healthful snacks, like baby carrots, really need to be eaten with a source of fat for us to absorb the beta carotene."
White was spurred on to pursue this research following a conversation with scientists at Procter & Gamble's Nutrition Science Institute. While studying beta-carotene absorption in their own labs, the P&G scientists noticed their supervisor eating a large green salad for lunch nearly every day, topped with a fat-free dressing. Curious as to whether he was actually depriving himself of important food components without the fat supplement, they asked White, who had conducted other research with Procter & Gamble, to check it out.
White and ISU graduate student Melody Brown undertook studies in the university's Center for Designing Foods to Improve Nutrition. Men and women, between the ages of 19 and 28, participated in the 12-week study, eating salads of spinach, romaine lettuce, cherry tomatoes and carrots, topped with Italian dressings containing 0, 6 or 28 grams of canola oil. Hourly blood samples were collected for 11 hours following each meal, and then sent to food scientists at Ohio State University to be tested with highly sensitive detection equipment.
Essentially no beta carotene absorption was observed when salads with fat-free dressing were eaten. A significantly greater absorption of lycopene, alpha- and beta-carotene was recorded when salads were eaten with full-fat dressings than with reduced-fat dressings.
White's findings are published in the August issue of the American Journal of Clinical Nutrition.