Risks and Benefits of Consuming Edible Seaweeds
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Special Article Risks and benefits of consuming edible seaweeds Paul Cherry, Cathal O’Hara, Pamela J. Magee, Emeir M. McSorley, and Philip J. Allsopp Recent interest in seaweeds as a source of macronutrients, micronutrients, and bio- active components has highlighted prospective applications within the functional food and nutraceutical industries, with impetus toward the alleviation of risk factors associated with noncommunicable diseases such as obesity, type 2 diabetes, and cardiovascular disease. This narrative review summarizes the nutritional composi- tion of edible seaweeds; evaluates the evidence regarding the health benefits of whole seaweeds, extracted bioactive components, and seaweed-based food prod- ucts in humans; and assesses the potential adverse effects of edible seaweeds, including those related to ingestion of excess iodine and arsenic. If the potential functional food and nutraceutical applications of seaweeds are to be realized, more evidence from human intervention studies is needed to evaluate the nutritional benefits of seaweeds and the efficacy of their purported bioactive components. Mechanistic evidence, in particular, is imperative to substantiate health claims. INTRODUCTION components of interest to industry include isolated pol- ysaccharides (eg, alginate, fucoidan), proteins (eg, phy- Edible seaweeds (macroalgae) have the potential to pro- cobiliproteins), polyphenols (eg, phlorotannins), vide a rich and sustainable source of macronutrients carotenoids (eg, fucoxanthin), and n-3 long-chain poly- and micronutrients to the human diet, particularly in unsaturated fatty acids (eg, eicosapentaenoic acid). regions where seaweed makes a significant contribution Scientific experiments and human studies to date have to regular meals, eg, in Japan, where approximately focused predominantly on brown seaweeds and deriva- one-fifth of meals contain seaweed.1–3 Inclusion of sea- tives, largely because of their commercial abundance weeds in Western diets has traditionally been limited to and perceived sustainability. artisanal practices and coastal communities but has Despite the nutritional attributes of red seaweeds gained wider consumer interest in recent years, cour- such as Porphyra spp (also known as nori) and tesy of the health-food industry.4 The recent surge of in- Palmaria palmata (dulse), which have a high protein terest in seaweed is fueled by attention on the bioactive content, relatively few investigations have focused on components of seaweed, which have potential applica- red seaweeds as a source of bioactive components. tions in the lucrative functional food and nutraceutical Current understanding of the health-promoting activi- industries, with impetus toward the alleviation of meta- ties of red seaweeds derives from an abundance of bolic risk factors such as hyperglycemia, hypercholester- in vitro studies and in vivo animal studies. There are olemia, and hyperlipidemia.5 The candidate bioactive only limited reports of green seaweeds contributing to Affiliation: P. Cherry, C. O’Hara, P.J. Magee, E.M. McSorley, and P.J. Allsopp are with the Nutrition Innovation Centre for Food and Health, School of Biomedical Sciences, Ulster University, Coleraine, United Kingdom. C. O’Hara is with VOYA Products Limited, County Sligo, Ireland. Correspondence: P.J. Allsopp, Nutrition Innovation Centre for Food and Health, School of Biomedical Sciences, Ulster University, Cromore Road, Coleraine, Co. Londonderry BT52 1SA, United Kingdom. Email: [email protected]. Key words: functional foods, heavy metals, marine bioactives, nutrition, seaweed. VC The Author(s) 2019. Published by Oxford University Press on behalf of the International Life Sciences Institute. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs licence (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reproduction and distribution of the work, in any medium, provided the original work is not altered or transformed in any way, and that the work is properly cited. For commercial re-use, please [email protected] doi: 10.1093/nutrit/nuy066 Nutrition ReviewsVR Vol. 77(5):307–329 307 dietary intake of either essential nutrients or bioactive the available evidence and outlines the potential risks components, despite the potential for transient algal and health benefits of consuming whole seaweeds, blooms to be exploited.6 extracted bioactive components, and seaweed-based Aquaculture is recognized as the most sustainable food products in humans. Additionally, it identifies fu- means of seaweed production and accounts for approxi- ture opportunities for functional food and nutraceutical mately 27.3 million tonnes (96%) of global seaweed pro- applications. duction per annum, yet the growing demand for seaweed-based food ingredients calls for more estab- NUTRITIONAL COMPOSITION OF EDIBLE SEAWEEDS lished guidelines and regulations to ensure sustainabil- ity.7 Future considerations for stakeholder management A number of edible seaweeds are recognized as novel include resource ownership; best practices for cultiva- foods in Europe, although the nutritional composition tion; harvesting rights/licensing; certification/validation of brown, red, and green seaweeds varies between spe- of origin; overexploitation; biomass regrowth; environ- cies, season, and ecology of the harvesting location.15 mental impacts; and the development of a sustainable Therefore, there is a need to characterize the composi- value chain within the agrifood sector.2 tion of seaweeds in relation to the influence of location An abundance of commercially available seaweed and seasonality on seaweed content. Current efforts to cat- products, including both whole seaweed and seaweed alog information on the variability of nutritional composi- extracts, are marketed both directly and indirectly as tion will facilitate the identification of optimal harvesting value-added products for the promotion of health in the periods and/or locations for a given species. Such informa- supplement market. The health claims associated with tion would aid the functional food industry in targeting seaweed products are often based on insufficient (or optimal conditions for isolating specific bioactive compo- completely absent) evidence from human intervention nents.16–18 Table 1,17,19–32 Table 2,19–22,26,27,29–31,33–42 and studies to substantiate such statements. Furthermore, Table 319–24,26,27,29,30,36,43–53 present the macronutrient there are considerable safety concerns related to poten- content of multiple brown, red, and green seaweeds, tial adverse events associated with seaweed consump- respectively, and consider a 5-g serving relative to tion, particularly in light of the variable and potentially reference nutrient intakes. To provide a basis for dangerously high concentrations of iodine and heavy comparison, Tables S1 and S2 in the Supporting metals (including arsenic species) in certain seaweeds.8,9 Informationonlinepresentthesamenutritionalin- There is currently limited legislation to require food or formation for a selection of dried seaweed products supplement companies to disclose mineral, heavy metal, commercially available throughout the United or iodine content of seaweed products or to provide KingdomandtheRepublicofIreland. guidance on a safe portion size of certain whole sea- weeds in order to prevent excess intakes.4 Ultimately, if Protein seaweeds are to contribute to future global food secu- rity, either in their whole form or via extraction of their The protein content of seaweed has gained considerable nutrients, the industry should develop a sustainable attention, given the emerging challenges to improve heavy metal/iodine monitoring program or, alterna- food security by identifying alternative and sustainable tively, identify novel processing technologies to ensure protein sources.54 As outlined in Tables 1, 2, and 3, the that unsafe components such as arsenic are minimized protein content ranges from 5.02% to 19.66% in brown to safe levels, thus protecting the food chain.2,10–14 seaweeds; from 0.67% to 45.0% in red seaweeds; and The health benefits of seaweed, beyond the provi- from 3.42% to 29.80% in green seaweeds. A 5-g portion sion of essential nutrients, have been supported by of dried brown, red, and green seaweed corresponds, in vitro studies and some animal studies; however, respectively, to a maximum of 1.97%, 4.5%, and 2.98% many of these studies have inappropriate biomarkers to of the Reference Nutrient Intake for protein. On a substantiate a claim and have not progressed to suitably gram-for-gram basis, seaweeds have protein and amino designed human intervention trials to evaluate efficacy. acid contents comparable to those of beef; however, sea- The limited evidence that does exist makes some sea- weeds are consumed in much smaller quantities.55 It weed components attractive as functional food ingre- should also be noted that the protein content of seaweed dients, but more human evidence (including is often derived from total nitrogen by using a conver- mechanistic evidence) is needed to evaluate both the sion factor of 6.25 (Kjeldahl method), which likely pro- nutritional benefit conferred and the efficacy of pur- duces an overestimate, given the nonprotein sources of ported bioactives and to determine any potential ad- nitrogen in seaweed. Hence, species-specific conversion verse effects. Through an evaluation of the nutritional factors ranging from