July 27, 2004 -- Eating your salad or carrot sticks with a little fatty salad dressing may actually be better for your health than pouring on the fat-free stuff.
A new study shows that eating fresh vegetables with a little fat, such as oil-based salad dressings or cheese, helps the body absorb valuable nutrients found in vegetables, such as lycopene and beta-carotene, which have been shown to help prevent heart disease and cancer.
In contrast, eating a salad without any fat in it may deprive your body of these healthy nutrients, which are known as carotenoids.
"We're certainly not advocating a high-fat diet, or one filled with full-fat salad dressing," says researcher Wendy White, associate professor of food science and nutrition at Iowa State University, in a news release. "Our findings are actually consistent with U.S. dietary guidelines, which support a moderate diet, rather than one very low, in fat."
"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," says White. "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."
Researchers say that the popularity of fat-free and low-fat salad dressings has grown in the last 10 years, and 20% of men and 33% of women say they always choose low-calorie rather than full-calorie salad dressings.
Fat Helps the Body Absorb Nutrients
Vegetables commonly found in salads are essentially fat-free and are a rich source of healthy carotenoids. In order for these carotenoids to be absorbed by the human digestive system, fat is needed. But researchers say exactly how much fat is needed to provide optimal absorption of these nutrients is not clearly defined.
In the study, which appears in the August issue of the American Journal of Clinical Nutrition, researchers compared nutrient absorption after eating salads with varying levels of fat.
Seven healthy men and women ate salads of spinach, romaine lettuce, cherry tomatoes, and carrots topped with Italian dressings containing 0, 6 (0.2 ounces), or 28 grams (almost 1 ounce) of canola oil on different occasions during a 12-week period. Hourly blood samples were taken for 11 hours after the meal and tested for nutrient absorption.
The study found that only negligible amounts of alpha- and beta-carotene and lycopene were detected in the blood after eating a salad with fat-free dressing. Significantly more of these substances, known as carotenoids, were detected in the blood after eating salads with reduced-fat dressing or full-fat dressings.
Researchers say this study shows that the minimum amount of fat required for optimal absorption of these nutrients from the salads is more than 6 grams of added fat. But because salads are often consumed with other items that contain fat, the use of a reduced-fat salad dressing may still allow the body to reap the maximum nutritional benefits of fresh vegetables.