Eating spinach raw, preferably along with healthy fats, maximizes the levels of nutrients available, according to new research.

New European research has found that eating spinach uncooked in the form of a smoothie or juice is the best way to obtain the antioxidant lutein, especially when healthy fats are added to aid absorption.

Carried out by researchers at Linköping University, Sweden, the new study looked at different ways of preparing spinach to maximize the amount of lutein available after cooking.

Lutein is a natural fat-soluble pigment found in plants. Dark green vegetables contain particularly high levels. However, like many other nutrients, levels of lutein are decreased by cooking.

The researchers chose to study spinach as it contains comparatively high levels of lutein, and is one of the more popular dark green vegetables. To replicate how it is prepared in the home, the team purchased baby spinach at a supermarket and fried, steamed or boiled it for up to 90 minutes, measuring the lutein content at different times.

The findings, published in the journal Food Chemistry, showed that heating times and cooking methods are both important for retaining lutein.

The longer spinach is boiled, the less lutein it retains, and when spinach is fried at high temperature, a large amount of lutein is lost after only two minutes.

"What is unique about this study is that we have used preparation methods that are often used when cooking food at home, and we have compared several temperatures and heating times. We have also investigated methods of preparation in which the spinach is eaten cold, such as in salads and smoothies," said study author Lena Jonasson.

The team also looked at the effect of reheating spinach in a microwave as part of a packed lunch, a common practice. They found that microwave heating appeared to partly compensate for the previous cooking method, with more lutein released from the spinach and made available for the body as the plant structure is broken down further by the microwave.

However, the researchers concluded that it's best to eat spinach uncooked. 

"Best is not to heat the spinach at all. And even better is to make a smoothie and add fat from dairy products, such as cream, milk or yoghurt. When the spinach is chopped into small pieces, more lutein is released from the leaves, and the fat increases the solubility of the lutein in the fluid," said Rosanna Chung, principal study author.

In an earlier study, the team found that lutein can reduce inflammation in immune cells from patients with coronary artery disease. Low-grade chronic inflammation is linked to an increased risk of heart attack.

They also showed that lutein can be stored in immune cells, meaning that it is possible to build up a reserve of lutein within your body.

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