Published in the journal Molecular Nutrition and Food Research, the Purdue study fed 29 diners a series of salads with different dressings — one with saturated fat (in this case, butter), one with polyunsaturated fat (corn oil), and one with monounsaturated fat (canola oil). After consuming each salad, the subjects gave a blood sample so that researchers could measure how well their bodies had absorbed the fat-soluble carotenoids — important antioxidants like lutein, lycopene, and beta-carotene that help protect against a wide range of chronic diseases — contained in the salad.
The results showed that the dressing composed primarily of canola oil was most efficient at helping the body absorb the ingested carotenoids. In other words, this dressing provided the biggest carotenoid punch in the smallest volume, compared to the other dressings. The butter- and corn oil-based dressings both required higher doses in order to achieve the same level of carotenoid presence in the blood.
So, monounsaturated fat — also found in olive oil and sesame oil, as well as avocado and peanut butter — is probably the way to go when choosing a dressing. But, the more important takeaway here is that your body needs at least some fat in order to get the most out of your salad. Yet more proof that our collective fat-phobia isn't actually helping us as much as we think.