12 January - 20 June 2016

Can adding soybean oil to salad increase the absorption of nutrients?

Adding around 32 grams of soybean oil dressing to salad may increase the absorption of nutrients according to a small study published in the American Journal of Clinical Nutrition. The study led by scientists from the Iowa State University and funded by Unilever found that the oil increased the absorption of seven different micronutrients including four carotenoids (α-carotene, β-carotene, lutein and lycopene), two forms of vitamin E and vitamin K.

Adding around 32 grams of soybean oil dressing to salad may increase the absorption of nutrients according to a small study published in the American Journal of Clinical Nutrition.   The study led by scientists from the Iowa State University and funded by Unilever found that the oil increased the absorption of seven different micronutrients including four carotenoids (α-carotene, β-carotene, lutein and lycopene), two forms of vitamin E and vitamin K.

White et al. recruited 12 healthy women aged 19-39 years old who consumed salads with various amounts of soybean oil (0, 2, 4, 8, or 32 g per 60 g serving).  The salad contained 48 g spinach, 48 g romaine, 66 g shredded carrots and 85 g cherry tomatoes.  On days 1-3 the participants were given a list of food sources of carotenoids, phylloquinone, retinoids and tocopherols they should avoid.  On day four the participants consumed a meal with a low content of carotenoids and fat-soluble vitamins and then fasted overnight. On the fifth day, the participants consumed the test salad with bottled water. This process was used for each test oil.  Blood samples were collected and analysed for nutrients.  White et al. analysed the nutrient content of the salad vegetables from each of the 5 study periods. They also analysed the nutrient content of the oil and reported that the dressings contained “low residual amounts of tocopherols and no detectable carotenoids or phylloquinone.” 

White et al found that “across the entire 0-32 g range of soya-bean oil the average absorption of α-carotene, lycopene and retinyl palmitate and vitamin A could be largely predicted by the amount of soybean oil added to fresh vegetables.”  For β-carotene the scientists report that for 0-8 g soybean oil, the absorption was linearly related to the amount of oil. There was “minor linear increases in the absorption of lutein, α-tocopherol, and total tocopherol over a more limited range of 0-4 g soybean oil.” They note that these finding therefore suggest that “lutein, α-tocopherol and total tocopherol bioavailability may benefit more from amount > 4 g soybean oil”.  Absorption of all carotenoids and fat-soluble vitamins was highest with 32 g oil.  

The team discuss their findings and suggest mechanisms for the enhancing effect of the soybean oil, including “providing an oil phase in which the fat-soluble carotenoids and vitamins could be solubilised or dispersed during emulsification.” Whilst the scientists report some variation amongst the subjects, White is quoted in a press release, as saying “For most people, the oil is going to benefit nutrient absorption.  The average trend, which was statistically significant, was for increased absorption.”  The study notes “that those who absorbed more of one carotenoid and fat-soluble vitamin also tended to absorb more of the others.”  However White et al. says that consumers should not drench salad with oil and should follow US recommendation of about two tablespoons of oil per day. 

RSSL’s offers a full vitamin analysis service and can to analyse for carotenoids in supplements and foodstuffs. To find out more please contact Customer Services telephone 0118 918 4076 or e-mail enquiries@rssl.com

RSSL has considerable expertise in all aspects of fat analysis and fatty acid profiling and can analyse for both tocopherols and tocotrienols (forms of vitamin E).  To find out more please contact Customer Services telephone 0118 918 4076 or e-mail enquiries@rssl.com

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