Coconut milk is the plant-based milk that works best when it comes to liberating the antioxidant lutein from spinach in green smoothies, according to a study published in the scientific journal Nutrients. Comparatively, high-fat and medium-fat cow’s milk were found to improve lutein liberation by 36 percent and 30 percent, respectively. “Cow’s milk with a high fat content as well as coconut milk improved lutein liberation. Among the plant-based milk, the researchers also discovered that soy milk was less effective than water when it comes to liberating lutein. “We saw that soy milk was actually less effective than water when it comes to liberating lutein in spinach smoothies,” Neelissen said.