If steaming or boiling kale isn’t quite your style, there’s new research indicating that tossing it with oil might actually enhance nutrient absorption. Researchers from the University of Missouri found that kale without dietary fat showed limited absorption of certain carotenoids—nutrients that contribute to eye, heart, and immune health.
Using a lab model to replicate human digestion, the team tested kale in four scenarios: raw, cooked, dressed or sauced after cooking, and cooked directly in sauces. Their findings, which appeared this month in the journal Food Nutrition, challenge the common perception that raw kale is the healthiest option.
The study revealed that raw kale on its own had minimal absorbable carotenoids, and cooking it without added fat further lowered these levels. However, when oil-based dressings or specially designed “nanoemulsion” sauces were introduced, the bioaccessibility of carotenoids improved significantly. Interestingly, the digestion model showed higher carotenoid availability regardless of whether the kale was consumed raw or cooked, as long as oil was present.
“Kale is rich in carotenoids like lutein, alpha-carotene, and beta-carotene, all of which are beneficial for health,” said Luoji (Vanessa) Zhang, an assistant professor involved in the study. “The challenge is that these nutrients are fat-soluble, making them harder for our bodies to absorb.”
It’s clear that fat-soluble nutrients need some dietary fat for better absorption, so pairing kale with sources like olive oil or oil-based dressings can enhance nutrient uptake.
Nicolette Pace, a registered dietitian based in New York, recommends a “plant-to-plant” approach, blending vegetables with plant-based fats—such as avocado, various oils, and peanut butter—to boost nutrient absorption. She mentions that while a generous amount of oil isn’t necessary, a small drizzle of olive oil not only makes nutrient absorption better but also enhances flavor.
This study offers a fresh perspective on how to increase nutrient bioavailability in vegetables, although the results come from a simulated environment rather than actual human absorption. Researchers also noted that these findings could inform future dressings and sauces aimed at maximizing nutrient accessibility.
Past studies have shown similar trends, indicating that dietary fats can enhance nutrient absorption from vegetables. In fact, research from Iowa State University demonstrates that adding oil to salads can significantly heighten nutrient absorption, while a study from the University of Barcelona found that cooking vegetables in extra virgin olive oil helps release more beneficial compounds.
Different fats yield different results, and heat can degrade some vitamins, so it’s important to consider how one prepares meals. The Missouri study digs deeper into how fat might affect kale specifically, showcasing nuances that previous research hinted at.
Though this study uses a model that can’t perfectly mimic human digestive processes, the insights are relevant for specific kale varieties and the types of nanoemulsions tested. The idea that fat aids in absorbing fat-soluble nutrients is well accepted, but this study contributes additional clarity to our understanding of kale.
