Kale has long been crowned a “superfood,” praised for its rich antioxidant and nutrient content – but new research suggests many of those perks go untapped unless you pair the leaves with a simple addition that boosts your body's ability to absorb the health benefits.
Researchers at the University of Missouri's College of Agriculture, Food and Natural Resources (CAFNR) have demonstrated that kale's nutritional load is poorly absorbed by the human body when eaten raw or cooked – because it needs fat for solubility.
“Kale is a nutrient-rich vegetable that contains carotenoids, including lutein, α-carotene and β-carotene, which have beneficial effects on overall health,” said Ruojie (Vanessa) Zhang, assistant professor in the Division of Food, Nutrition and Exercise Sciences at CAFNR. “The problem is our bodies have a hard time absorbing these nutrients because they are fat-soluble rather than water-soluble.”
The researchers investigated whether cooking kale or adding specially designed condiments could boost the bioavailability of the vegetable's carotenoids as well as vitamins C and E. A lab model of human digestion was then used to test different kale preparation methods – raw, cooked, raw in dressing and cooked in sauce. The in vitro gastrointestinal tract model, including the mouth, stomach and small intestine phases, was used to simulate the human digestive processes that occur after ingestion of the kale, composed of digestive fluids formulated in a previous study.
What they found was that raw kale results in very limited carotenoids being absorbed by the body, and cooking it alone is even worse. However, when the team added a specific oil-in-water nanoemulsion, far more carotenoids were absorbed through digestion, in both raw and cooked models, when the dressing/sauce was mixed in on the plate.
"These exipient emulsions typically consist of emulsifier-coated oil droplets dispersed in an aqueous medium," the resesrchers noted. "The type and amount oil present is carefully controlled to ensure that it is rapidly digestion in the small intestine, and then generates mixed micelles that can efficiently solubilize the hydrophobic nutraceuticals in the gastrointestinal fluids."
Nanoemulsions are most commonly a mix of oil and water but distinct – the dispersed droplets are extremely small, typically in the range of ~20–200 nanometres (nm). With food, they're used to encapsulate oils, vitamins, flavours and nutrients (like carotenoids) to enhance bioavailability and digestibility. They're being increasingly studied as a method of improving nutrient absorption – but the science remains a work in progress.
It's a simple but fascinating demonstration of how a health food, at face value, may seem to be better for us than it is – and how combinations of foods can help us make the most of what we're eating. For example, there's an established body of evidence that shows how using vitamin C as an adjunct agent facilitates more iron absorption from leafy greens like spinach and kale.
“Our team is committed to advancing food science with the goal of improving human health through the development of innovative foods and technologies,” Zhang said. “We believe impactful science can drive meaningful change in global nutrition and well-being, and we’re excited to contribute to that mission.”
The researchers are now looking at developing new condiments that can enhance the absorption of nutrients from kale and other vegetables.
The study was published in the journal Food Nutrition.
Source: University of Missouri
