João P. Trigo1,*, Mar Vall-Llosera1, Susanne Bryngelsson2, Ingrid Undeland1
1Department of Biology and Biological Engineering – Food and Nutrition Science, Chalmers University of Technology, Gothenburg, Sweden
2RISE Research Institutes of Sweden, Gothenburg, Sweden
The potential health benefits associated with seaweed consumption is a hotly debated topic that often arises when advocating the inclusion of seaweed in the Western diet. Its perception as a “healthy” food commodity is likely due to the abundance of dietary fibers, essential elements, and in vitro bioactive phenolic compounds. However, clinical evidence is needed to corroborate promising in vitro findings. This narrative review analysed randomized-controlled interventional trials (RCTs) from the last 22 years that tested whole seaweed. We aimed at critically assessing the methodology and Cochrane risk-of-bias as well as existing links between seaweed consumption and health endpoints.
Of the 26 RCTs collected, the most studied primary outcomes were blood glucose, blood lipids, and urinary iodine reflecting a focus on metabolic disorders and thyroid function. For the first two, the percentage of RCTs reporting significant reductions after the intervention compared to control diets was 40 and 18%, respectively, whereas 57% reported an increase in urinary iodine. A preliminary overall risk-of-bias judgment revealed that around 83% of all RCTs were at high-risk of bias, which altogether limits the possibility to draw firm conclusions. Regarding methodology, a total of 22 RCTs used dried seaweed with large variations in pre-treatment and drying methods, which impairs potential comparisons between RCTs testing the same species. Also, 15 RCTs opted for encapsulated seaweed, although most did not report potential flavour differences/similarities versus the placebo.
Overall, more well-designed RCTs are warranted to generate stronger clinical evidence on the role that seaweed can play in disease prevention.