Carotenoid Bioavailability Higher In Salads With Full-fat Dressings

AMES, Iowa--The appearance of carotenoids in plasma cylomicrons after ingesting fresh vegetable salads is higher when using a full-fat dressing, according to a study published in the August issue of the American Journal of Nutrition (80, 2:396-403, 2004) (www.ajcn.org).

The small study, led by researchers from Iowa State University, involved seven subjects each consuming three salads containing equivalent amounts of spinach, romaine lettuce, cherry tomatoes and carrots with salad dressings containing 0, 6 or 28 g of canola oil.

The salads were consumed in random order and separated by washout periods of two weeks. Blood samples were collected hourly for 12 hours after consumption. Chylomicrons were isolated by ultracentrifugation, and carotenoid absorption was analyzed by HPLC with coulometric array detection.

After ingestion of the salads with fat-free salad dressing, the appearance of alpha-carotene, beta-carotene and lycopene in chylomicrons was negligible, showing essentially no absorption of carotenoids. After ingestion of the salads with reduced-fat salad dressing, the appearance of carotenoids in plasma chylomicrons increased relative to that after ingestion of the salads with fat-free salad dressing. Similarly, the appearance of carotenoids in plasma chylomicrons was higher after the ingestion of salads with full-fat than with reduced-fat salad dressing. The researchers concluded essentially no absorption of carotenoids was observed when salads with fat-free salad dressing were consumed, and a substantially greater absorption of carotenoids was observed when salads were consumed with full-fat than with reduced-fat or fat-free salad dressings.