Simple dressing trick unlocks hidden nutrients in kale

Many people load their salads with kale because they want a nutrient boost. The vegetable has a strong reputation, yet a new study shows that the way we prepare it often decides how much benefit we truly get.

According to the research, some meals allow our bodies to draw more value from kale, while others leave most nutrients trapped inside its leaves.

Nutrients that resist breakdown

Kale offers lutein, α carotene, β carotene, tocopherols, vitamin C and polyphenols. These compounds support eye function, immunity and cell repair.

“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.

Yet these nutrients hide within plant organelles that resist breakdown during digestion.

The study explains that carotenoids struggle to move through the digestive fluids because they are fat soluble. Water alone cannot carry them into the micelles that transport them through the gut.

Without support from fats, much of kale’s goodness passes through the body untouched.

Why kale loses nutrients

The researchers noted that raw kale releases very little of its carotenoids in the digestive model. Cooking does not solve the issue because kale tissue already breaks down easily during digestion.

Unlike carrots or tomatoes, which strongly resist breakdown until heated, kale has a looser tissue structure. This feature limits how much heat can improve nutrient release.

The study also shows that the digestive process changes the structure of plant fragments. As the kale moves through the mouth, stomach and intestine, the fragments loosen further, yet not enough to let carotenoids become fully accessible without fat.

Oil boosts nutrient release

Once researchers added oil based dressings or nano sized emulsions, carotenoid release improved sharply. These emulsions act as carriers with droplets that can enter softened plant tissue as digestion progresses.

The oil droplets also break down into substances that form mixed micelles, which transport fat soluble compounds. This combination makes lutein, α carotene and β carotene far more available to the body.

The model showed that raw and cooked kale paired with emulsions produced much higher carotenoid levels in the micelle phase. This confirms that oil plays the central role in lifting nutrient release, not cooking time alone.

Kale tissue and heat

Many kitchens simmer greens with sauce rather than adding dressing later. The researchers tested this habit and found that cooking kale with an oil-rich sauce works as well as adding it after cooking.

The emulsion stays effective because the heat does not damage its ability to support digestion. Kale tissue does not gain much from extra heating because it already breaks down quickly during digestion.

This means everyday cooking styles can help nutrient release without demanding major changes. People can heat the sauce with the kale or combine it later and still gain the same improvement.

Unlocking nutrients in kale

The study highlights a key insight: different vegetables release nutrients in different ways. Carrots and tomatoes often gain more carotenoid release after heating because their tissues remain firm until cooked. Kale behaves differently.

Its structure loosens fast in the digestive tract, so heat alone offers little benefit. The emulsion becomes the real driver of nutrient movement into micelles.

The researchers also noted that kale carries carotenoids inside chromoplasts and chloroplasts.

Digestion can free some of these compounds, but complete release still depends on the presence of dietary fat. The emulsions help move the carotenoids into droplets and later into mixed micelles.

Meaningful change in global nutrition

“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 findings show how thoughtful food design can help people get more from daily vegetables.

The study also highlights how plant structure influences health benefits, and why pairing leafy greens with the right fats matters. As scientists refine these emulsions, they hope to develop dressings that raise nutrient use even further.

The research is published in the journal Food Nutrition.

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