Red seaweeds have been prevalent as a culinary staple in various regions of Asia for thousands of years, and many researchers have pointed to these seaweeds as a potential reason for why Japan has the lowest colon cancer patients per capita compared with any other part of the world.
 
In a recent chemical study on red seaweeds, published in the journal Marine Drugs, researchers posited that a specific sugar unique to red seaweed could be responsible for conferring health benefits as they relate to colon cancer outcomes.
 
“In the past, people have wondered why the number of colon cancer patients in Japan is the lowest in the world,” Yong-Su Jin, food microbiology professor, said. “Many assumed that it was due to some aspect of the Japanese diet or lifestyle. We wanted to ask whether their seaweed diet was connected to the lower frequency of colon cancer.”
 
Several studies on Asian populations found that regular seaweed consumption had a dose-respondent relationship with reduced incidences of colon, colorectal, and breast cancer. However, it is unclear which component of red seaweeds was responsible for this risk reduction.
 
In the present study, researchers from the Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign broke down the structure of different red seaweed types using enzymes, and tested the sugars that were produced. Among the six different sugars, agarotriose and 3,6-anhydro-L-galactose (AHG) showed the most promise.
 
“After we produced these sugars, we tested their prebiotic activity using the bacteria Bifidobacterium longum ssp. Infantis,” Eun Ju Yun, a former postdoctoral researcher at the Carl R. Woese Institute, said.
 
B. infantis is a probiotic bacterium which naturally colonizes the guts of infants, and is associated with a number of health benefits. Among the seaweed-derived sugars, the bacteria was only able to consume agarotriose, indicating that this sugar works as a prebiotic by improving the growth of B. infantis.
 
“We also tested another strain, B. kashiwanohense, and found that it also consumed agarotriose,” Jin said. “These results show us that when we eat red seaweed, it gets broken down in the gut and releases these sugars which serve as food for the probiotic bacteria. It could help explain why Japanese populations are healthier compared to others.”
 
The researchers also found that AHG was able to inhibit the growth of human cancer cells in vitro by triggering cell death – at the same time, it didn’t affect the growth of normal cells in lab settings.
 
“There is a lot of information on how red seaweeds are degraded by microorganisms in the ocean and in the human body,” Kyoung Heon Kim, a professor of biotechnology and the co-advisor on the study, said. “Our work explains why red seaweeds are beneficial by providing the molecular mechanism. We will continue studying their function in animal models and hopefully we will be able to use them as a therapeutic agent in the future.”