In the wake of the low-fat trend of the 1980s, and the subsequent realization that fat is not necessarily the enemy in human health and nutrition, several studies have emerged that establish this macronutrient as absolutely essential. Fat has proven important not only in its own right, but as an important catalyst for the absorption of other nutrients. This observation was reinforced recently in a human trial examining the effect of various forms of salad dressing.
Researchers fed subjects salads topped off with saturated, monounsaturated and polyunsaturated fat-based dressings and tested their blood for absorption of fat-soluble carotenoids—compounds such as lutein, lycopene, beta-carotene and zeaxanthin. These carotenoids are associated with a reduced risk of several degenerative diseases, including cancer, cardiovascular disease and macular degeneration.
For the study, 29 people were fed salads dressed with butter serving as the saturated fat, canola oil as the monounsaturated fat and corn oil as the polyunsaturated fat. Each type of dressing was also served in various quantitative categories of 3 fat grams, 8 fat grams or 20 fat grams per salad, respectively. The results proved highly interesting, indicating that while all types of fat aided in the absorption of nutrients, one variety emerged as superior.
Monounsaturated fat-rich dressings, such as canola and olive oil-based dressings, promoted equivalent carotenoid absorption regardless of serving size—yielding the equivalent benefit at 3 grams per salad as at 20 grams. As this difference in serving size represents a difference of just over 150 calories, these results suggest that this fat source could be a better choice for those seeking lower-fat options without sacrificing the absorption of health-promoting nutrients.
By comparison, the soybean oil—rich in polyunsaturated fat—was highly dependent on serving size; the more fat on the salad, the more carotenoids the subjects absorbed. The saturated fat butter dressing also exhibited this characteristic, although to a lesser extent. Overall, one central conclusion of the study is that some amount of fat is needed for optimal nutrient absorption, and that perhaps the era of fat-free salad dressing should come to a conclusion as well.
“If you want to utilize more from your fruits and vegetables, you have to pair them correctly with fat-based dressings,” said Mario Ferruzzi, the study’s lead author and 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.”