Study: Reducing heat in spinach preparation can boost lutein intake

02 Jan 2019 --- Consuming spinach in a smoothie or juice may deliver the highest antioxidant lutein levels, according to researchers at Linköping University (LiU), in Sweden. Dark green vegetables typically contain high levels of lutein and the study sought to determine which cooking method maximized the levels of lutein ending up in our final meals.

Lutein, a natural fat-soluble pigment abundant in dark leafy vegetables, such as spinach, has been associated with several health-promoting effects, such as reducing inflammation. The antioxidant is also a star ingredient in the eye health segment. According to Innova Market Insights data, new product launches (including supplements) tracked featuring lutein, as well as carotenoid zeaxanthin, saw a compound annual growth rate (CAGR) of 25 percent and 18 percent, respectively, between 2012 and 2016, when 2012 is taken as a base of 100. 

The Swedish researchers investigated which method of preparation was the best for obtaining high lutein levels in the diet. They chose to study spinach, which contains comparatively high levels of lutein and is consumed in large amounts across a range of regions. Just as many other nutrients, lutein is degraded by heat.

“It is pretty well-known that lutein can be degraded by heat in laboratory settings so we did expect that the levels of lutein in food would be reduced by most domestic practices that involve heat. However, the extent that lutein was affected was surprising to us,” Rosanna Chung, principal author of the study, tells NutritionInsight.

“What is unique about this study is that we have used preparation methods that common 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,” says Lena Jonasson, Professor in the Department of Medical and Health Sciences and consultant in cardiology.

The study subjected the spinach to frying, steaming and boiling for up to 90 minutes.

The findings demonstrated how important the heating time is to lutein content. For example, when it came to boiling, the longer the spinach was boiled, the less lutein it retained. The cooking method also proved important; when spinach was fried at high temperatures, a large fraction of the lutein degraded after only two minutes.

The researchers also found that reheating the food in a microwave compensated for the loss of lutein in cooked food. In this way, more lutein was released from the spinach as the plant structure was broken down further by the microwave.

Overall, the findings point to ingesting spinach raw and unheated.

“It is 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 yogurt. 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,” explains Chung.

“Perhaps the food and nutrition industry could be more aware that food preparation methods could significantly affect the final nutritional content they claim their food products contain,” she adds.

More research is needed to identify how other factors could affect lutein content, such as storage and storage duration, Chung concludes.

The study has been financed with support from the Swedish Heart-Lung Foundation and the Swedish Research Council.

University of South Australia researchers also investigated the health halo of lutein, noting that higher levels of lutein status may be associated with higher levels of physical activity, which may contribute to a reduced risk of chronic disease. The findings could pave the way for lutein to be used in a wider range of supplements or sports products. The study noted that increasing lutein status, or possibly also the status of other carotenoids, is able to increase physical activity. 

Lutein has also been used in the cognitive health space, in nootropics, also known as “smart drugs” or “cognitive enhancers.” 

Within this space, OmniActive offers its Lutemax 2020, which delivers all three macular carotenoids (lutein, RR-zeaxanthin and RS (meso)-zeaxanthin). The ingredient has a particularly strong market potential for long-duration digital device users due to its beneficial effects on ocular health and performance, sleep quality and eye strain and fatigue during long-duration exposure to digital devices and screens.