Full-Fat Salad Dressings Enhance Bioabsorption of Carotenoids

Yael Waknine

August 05, 2004

Aug. 5, 2004 -- Full-fat salad dressings enhance bioavailability of carotenoids in salad consumption, according to the results of a study published in the August issue of the American Journal of Clinical Nutrition.

"The amount of dietary fat required for optimal bioavailability of carotenoids in plant matrices is not clearly defined," explain Melody J. Brown, MS, RD, and colleagues, from the Department of Food Science and Human Nutrition at Iowa State University in Ames. "By choosing reduced-fat or fat-free salad dressings, consumers could potentially compromise their exposure to the putative bioactivity of those carotenoids in preventing heart disease, cancer, and other chronic diseases."

To determine the effect of differing amounts of fat on intestinal absorption of carotenoids, investigators served equivalent vegetable salads with fat-free (0 g canola oil), reduced-fat (6 g canola oil), and full-fat (28 g canola oil) dressings to seven healthy, nonsmoking, normolipidemic subjects aged 19 to 28 years.

Each subject consumed the salads in random order, separated by washout periods of at least two weeks. Blood samples were collected hourly from 0 to 12 hours, and the postprandial carotenoid content of plasma chylomicrons were quantified using high-sensitivity high-pressure liquid chromatography with coulometric array.

Total carotenoid (α-carotene, β-carotene, and lycopene) content of each test salad was 31.3 mg. Chylomicron carotenoid content was negligible after salad ingestion with fat-free salad dressing, increased with use of low-fat dressing ( P < .04), and was highest with use of full-fat dressing ( P < .02).

"[I]n the absence of other sources of fat, the amount of fat in fat-free and reduced-fat salad dressings can be limiting in terms of the bioavailability of carotenoids," the authors comment.

While the threshold for optimal absorption of carotenoids in this study exceeded 6 g of added fat, a similar study reported that 3 to 5 g of fat are sufficient for optimal absorption of purified carotene from a cooked meal. "Our data suggest that 3 - 5 g fat should be considered a minimal amount that may not be sufficient for optimal bioaccessibility of carotenoids within the intact structures of plants," the authors write.

"As consumers make decisions about the use of fat-modified products, they need to be informed about the health implications regarding not only fat and energy but also regarding the overall quality of their diets," the authors point out. "[T]he use of lower-fat salad dressings may still afford consumers optimal access to the putative health benefits of carotenoids while promoting a diet moderate in total fat, as recommended by US Dietary Guidelines for Americans."

This study was funded by Proctor & Gamble Co., and two of the investigators are employees of the company.

Am J Clin Nutr. 2004;80:396-403

Reviewed by Gary D. Vogin, MD



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