Biomarkers of seaweed intake

Xi and Dragsted Genes & Nutrition (2019) 14:24 https://doi.org/10.1186/s12263-019-0648-4 REVIEW Open Access Biomarkers of seaweed intake Muyao Xi* and Lars O. Dragsted Abstract Seaweeds are marine macroalgae, some of which are edible. They are rich in specific dietary fibers and also contain other characteristic biological constituents. Biological activities have been investigated mainly in animal studies, while very few results are available from human studies. Biomarkers of food intake (BFIs) specific to seaweed could play an important role as objective measurements in observational studies and dietary intervention studies. Thus, the health effects of seaweeds can be explored and understood by discovering and applying BFIs. This review summarizes studies to identify candidate BFIs of seaweed intake. These BFIs are evaluated by a structured validation scheme. Hydroxytrifuhalol A, 7-hydroxyeckol, C-O-C dimer of phloroglucinol, diphloroethol, fucophloroethol, dioxinodehydroeckol, and/or their glucuronides or sulfate esters which all belong to the phlorotannins are considered candidate biomarkers for brown seaweed. Fucoxanthinol, the main metabolite of fucoxanthin, is also regarded as a candidate biomarker for brown seaweed. Further validation will be needed due to the very limited number of human studies. Further studies are also needed to identify additional candidate biomarkers, relevant specifically for the red and green seaweeds, for which no candidate biomarkers emerged from the literature search. Reliable BFIs should also ideally be found for the whole seaweed food group. Keywords: Biomarkers of food intake, Food exposure marker, Dietary assessment, Seaweed, Macroalgae Introduction Seaweeds or macroalgae, including species of brown, red, and green seaweeds, have been consumed as food in East Asia for a long time, but with more limited use in Europe and North America, except for the use of certain constituents as additives [1]. Recent interest in manufacturing and consuming high-value food products derived from seaweeds in Western countries is fueled by their proposed health benefits as well as by the introduction of Asian foods. Seaweeds may supply several nutrients and have been proposed to promote health and counteract a wide range of conditions and diseases, such as obesity, oxidative stress, hypertension, digestive problems, thrombosis, and even cancer [2–5]. However, this builds largely on very limited evidence from animal and in vitro studies. There are also a few trials with seaweeds or seaweed preparations in humans investigating effects on blood pressure [5, 6], appetite [7, 8], inflammation [9], and insulin response [10]. These health effects may * Correspondence: Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark originate from a variety of seaweed compounds, such as soluble fiber and carotenoids [6, 11–15]. Only one study has so far shown which compounds can be used as biomarkers of seaweed intake in overweight or obese subjects. In addition, no study has so far firmly documented longer-term effects of seaweed intake in human trials. In order to explore the relationship of seaweed intake with human health, it is important to measure intake accurately and it is therefore of importance to find specific compounds related to seaweed intake in general or to intake of any certain type of seaweed. Intake assessments in human studies to date largely depend on dietary assessment instruments such as food frequency questionnaires (FFQ) or 24-h recalls (R24h). These instruments are prone to recall bias and systematic errors [16]. Lack of compliance is also common in dietary intervention studies. Thus, it is difficult to evaluate the relationship between health effects and seaweed intake. Wellvalidated biomarkers of food intake (BFIs) may provide more objective estimates of actual intake. The objectives of this review are (1) to summarize information from the scientific literature related to © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Xi and Dragsted Genes & Nutrition (2019) 14:24 Page 2 of 13 compounds that may be currently used as, or considered as, candidate biomarkers for seaweed consumption [16] and (2) to provide systematic validation of the candidate BFIs based on recent methodology [17]. unless they contain information on unique seaweedderived compounds. Papers on contaminants and mineral contents of seaweed were also excluded from the search. Materials and methods Secondary search—evaluation of putative BFIs Defining the food group After identification of potential candidate BFIs from the primary literature search, a second search step was performed to evaluate the specificity of each putative BFI for seaweed intake. The second search was carried out by replacing (seaweed OR macroalgae) with (“the name and synonyms of the potential candidate biomarker” OR “the name and synonyms of potential candidate biomarker class”). In addition to the online databases listed above, hmdb [18] and foodb [19] were searched for each putative BFI in order to ascertain that they have not been measured previously in other foods. The full list of putative BFIs is shown in Table 1. Plausibility of the BFIs, i.e., the evaluation of whether the putative marker compound is likely to be uniquely present in seaweeds, was decided based on the secondary search; the final list of plausible BFIs are shown as the top 7 items of Table 2. Seaweeds are not well-defined in biological terms but cover largely the macroalgae. The macroalgae contain species belonging to several different phyla consisting of red, green, or brown algae and in some cases are considered to include also the prokaryotic photosynthetic cyanobacteria. Within the food group of seaweeds, there is a corresponding subdivision into three food subgroups, the red, brown, and green seaweeds, each with a large number of species. Although there are differences within and between these 3 subgroups of seaweed, it is considered of interest to find candidate biomarkers of the overall seaweed group as well as for each subgroup. Within each subgroup, there are many species that are likely to vary considerably in composition; however, the present review will not emphasize the detail of species or of varieties within species because little is known at this level of detail. Validation criteria of candidate BFIs Primary lite (...truncated)