Lead author of a study by Iowa State University, Professor Wendy White has discovered that eating salad with added fat in the form of soybean oil promotes the absorption of eight different micronutrients which promote human health.

Conversely, eating the same salad without the added oil lessens the likelihood that the body will absorb the nutrients.

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

Professor 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 - and 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 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, there was some variability among the subjects, which included 12 college-age women - who were chosen due to differences in the speed with which men and women metabolise the nutrients in question.

While the study results are interesting, Professor White cautioned that the findings don't mean salad eaters should drench their greens in dressing. Consumers should be perfectly comfortable with the U.S. dietary recommendation of about two tablespoons of oil per day.

The full study has been published in the American Journal of Clinical Nutrition.

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