Dairy and plant-based drinks may hinder lutein’s availability

They found that soy milk, whether with or without additives, showed significantly reduced lutein liberation when blended with spinach.

In addition, yoghurt, which is often used in smoothies, did not show particularly good results – a finding that was attributed to its fermentation method and type of culture used.

“In contrast to cow’s milk, none of the cow’s milk-derived yoghurt products were found to significantly improve lutein liberation compared to water,” wrote the paper’s authors, led by Rosanna Chung, principal study investigator and assistant professor at Sweden’s Linköping University.

“A weak fat-dependent trend was, however, observed amongst the yoghurt products. Although smoothies made with low-fat cow’s milk and low-fat yoghurt contained the same final fat content, low-fat cow’s milk resulted in significantly higher lutein levels.”

The findings, which were published last year in the journal Nutrients, have implications for smoothie manufacturers, as well as brands looking to position products around lutein’s benefits.

Lutein’s role in reducing low-grade inflammation and macular degeneration

The study highlights the need for beverage makers to carry out further testing of food companions for lipophilic ingredients like lutein, a bioactive compound linked to reduction of the low-grade inflammation characteristic of cardiovascular disease.

Research has also identified the compound’s role in maintaining eye health, with evidence pointing to its ability to delay the progression of age-related macular degeneration.

“As lutein is a fat-soluble compound, the findings of this study could potentially apply to other fat-soluble compounds, such as vitamin D,” Chung added.

“When formulating smoothies and other health products that contain fat-soluble active compounds, it may be more beneficial to combine with cow’s milk or coconut milk instead of soy milk.”

The influence of food interactions on nutrient absorption

Of significance, too, is the consideration of food matrix effects in nutritional research and dietary planning.

Growing evidence generated from simple food matrixes, defined by the interaction between two or three components, indicates that different components in food may interact with one another in the gut, leading to lowered or enhanced absorption.

“Nutritional research tends to not consider food interaction[s] or how the food was prepared or consumed, which could influent the final content of active compounds available in our bodies significantly,” explained Chung.

“Our diets are complex and diverse. This study highlights that not all dairy products or plant-based products are equal to one another without the categories.

“More research on food interaction in [a] real-life food matrix environment [is] needed to give more informed recommendations or to make dietary planning.”

Plant-based milks versus conventional dairy milk

The study builds on insights from the Plant Based Foods Institute's Plant-Based Migration Analysis Report, which revealed that 43% of plant-based customers who are new to or increasing their purchases of plant-based products choose plant-based milks over conventional dairy milk.

“Plant-based liquids have become increasingly common in smoothies,” said Jan Neelissen, doctorate student and one of the researchers behind the study.

“We saw that soy milk was actually less effective than water when it comes to liberating lutein in spinach smoothies. In other words, soy milk had a negative effect on lutein liberation in our study.”

The study also revealed that high-fat and medium-fat cow’s milk and coconut milk were superior in enhancing lutein dissolution.

“It is well documented that the fat globules in cow’s milk have emulsifying abilities for other common fat molecules such as triglycerides and cholesterols,” wrote Chung. “This study suggests that the milk fat globules could help lutein too.

“However, as soon as the cow’s milk [is] fermented into yoghurts, the structures of fat globules would change, and its emulsifying abilities would be lowered. Similarly, we also found coconut milk [has] comparable effects [to] high-fat and medium-fat cow’s milk.

“Although it is not well documented, some suggested that proteins in coconut milk could emulsify fat-soluble compounds. Therefore, we hypothesised that the effects we observed were due to the proteins from coconut milk. This hypothesis is yet to be tested.”