Oils & Nutrient Absorption

A spoonful of oil: Fats and oils help to unlock full nutritional benefits of veggies & salads.


Scientists in Iowa State University published new research suggesting that certain key oils make vegetable and salad even more nutritious.

The study led by Wendy White, an associate professor of food science and human nutrition, found that eating salad with added oil promotes the mechanism digestive absorption of eight different micronutrients which promote improved health. Conversely, eating the same salad without the added oil lessens thebodies ability to fully absorb key nutrients.

This study was peer-reviewed American Journal of Clinical Nutrition, and the results may ease the guilt of countless dieters who forfit adding dressing and Olive oil to their salads.

White's study found added oil aided in the absorption of seven different micronutrients in salad vegetables. Those nutrients include four carotenoids -- alpha and beta carotene, lutein and lycopene -- two forms of vitamin E and vitamin K. The oil also promoted the absorption of vitamin A, the eighth micronutrient tracked in the study, which formed in the intestine from the alpha and beta carotene. The new study builds on previous research from White's group that focused on alpha and beta carotene and lycopene.

White said "better absorption of the nutrients promotes a range of health benefits, including cancer prevention and eyesight preservation".

The study also found that the amount of oil added to the vegetables had a proportional relationship with the amount of nutrient absorption. That is, more oil means more absorption. In this case real butter would have positive benefits added to your veg intake.

"The best way to explain it would be to say that adding twice the amount of salad dressing leads to twice the nutrient absorption," White said.

That doesn't give salad eaters license to drench their greens in dressing, she cautioned. But she said consumers should be perfectly comfortable with the U.S. dietary recommendation of about two tablespoons of oil per day.

The study included 12 college-age women who consumed salads with various levels of soybean oil, a common ingredient in commercial salad dressings. The subjects then had their blood tested to measure the absorption of nutrients. Women were chosen for the trial due to differences in the speed with which men and women metabolize the nutrients in question.

The results showed maximal nutrient absorption occurred at around 32 grams of oil, which was the highest amount studied, or a little more than two tablespoons. However, White said she found some variability among the subjects.

"For most people, the oil is going to benefit nutrient absorption," she said. "The average trend, which was statistically significant, was for increased absorption."

Research collaborators include Yang Zhou, a former ISU postdoctoral researcher; Agatha Agustiana Crane, a former graduate research assistant in food science and human nutrition; Philip Dixon, a University Professor of Statistics, and Frits Quadt of Quadt Consultancy, among others.

So a few generous spoonfuls or cubes of real butter may indeed help you derive the optimal nutritional benefit from your salad & veggies; similar to traditional and Mediterranean dietary habits, enjoy. 


Journal Reference:

  1. Wendy S White, Yang Zhou, Agatha Crane, Philip Dixon, Frits Quadt, Leonard M Flendrig. Modeling the dose effects of soybean oil in salad dressing on carotenoid and fat-soluble vitamin bioavailability in salad vegetablesThe American Journal of Clinical Nutrition, 2017; 106 (4): 1041 DOI: 10.3945/%u200Bajcn.117.153635
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