The primary goal of this scoping review is to understand the varied aspects of research and consumption of macroalgae as potential food sources worldwide. We have distilled our findings into three main areas: the underexplored yet significant nutritional profile of macroalgae, the necessity of cultivating or harvesting them from uncontaminated environments, and the importance of grasping consumer attitudes and hesitations towards eating macroalgae. First, we highlight the nutritional potential of macroalgae, noting that among the 40 unique species we reviewed, we identified a plethora of essential nutrients, including vitamin B12, which is traditionally thought to be exclusive to animal products. Second, while acknowledging their nutritional benefits, it is critical to point out that edible algae might accumulate heavy metals and other pollutants if grown in polluted waters, due to their role in oceanic filtration. Yet, the current state of research does not allow for definitive conclusions on the safety of consuming algae. Lastly, we found that education level and food neophobia significantly influence algae consumption patterns. These factors could inform strategies for campaigns designed to encourage incorporating algae into sustainable diets, emphasizing the complexity and potential of macroalgae as a food source.
Nutritional Quality of Macroalgae
One of the key aspects we emphasize about the nutritional quality of macroalgae is their cobalamin content, commonly known as vitamin B12. This component generates optimism for their inclusion in plant-based diets, particularly for vegans (DRI 1998; Watanabe 2018). However, caution is advisable since evidence concerning the bioavailability of vitamin B12 in macroalgae remains limited (Dagnelie 1991). Currently, there is a lack of understanding about the specific forms of cobalamin found in these algae, including whether they exist as analogs or active forms suitable for human absorption (Slywitch 2022; Herrmann 2002). The human body cannot efficiently absorb and utilize analogous cobalamin due to its molecular structure, which is incompatible with the body’s metabolic processes (Slywitch 2022).
Insufficient studies on B12 absorption in humans mean that we currently lack reliable data to endorse non-animal B12 sources or to definitively identify which sources contain the vitamin's active form rather than inactive analogs (Rizzo 2016). Therefore, while algae show promise as a cobalamin source, further research is essential to confirm their bioavailability. Future comprehensive studies should include measurements of B12 in food and blood and assess markers of B12 function to verify the activity of the B12 form being utilized (Slywitch 2022).
The presence of unsaturated lipids in algae is also noteworthy. Typically, essential polyunsaturated fatty acids (PUFAs), including omega-3 fatty acids, are sourced from vegetable oils, fish oils, and other animal products (Shanab 2018). However, it is important to understand that for fish oils, the primary source of these PUFAs is not the fish themselves but the marine algae and phytoplankton they consume (Nordy 1989). This makes algae a direct, valuable source of these fatty acids, especially long-chain omega-3s like DHA, which have recognized health benefits supported by epidemiological studies and controlled intervention trials (Conquer & Holub 1996; Holub 2009; Cottin et al. 2011). The literature also highlights eicosapentaenoic acid n-3 (EPA) as a prevalent polyunsaturated fatty acid in marine vegetables such as algae (Wells 2017), often found alongside arachidonic acid, particularly in red algae (Wells 2017; Norziah & Ching 2000; Wen et al. 2000).
Regarding the fat content of algae, a study examining seven North Sea seaweed species discovered that Palmaria palmata contains the highest concentration of n-3 eicosapentaenoic acid (EPA), at about 8.3 mg/g of dry weight (Van Ginneken et al. 2011). This discovery is consistent with previous research indicating that several seaweed species, including Himanthalia elongata, Undaria pinnatifida, and Porphyra sp., have high levels of EPA. These levels are beneficial for reducing the risks of heart diseases, thrombosis, and arteriosclerosis (Plaza, 2008). Furthermore, another study analyzing the lipid profiles of three different seaweed species found that Eucheuma cottonii particularly stands out with notably high levels of this fatty acid, comprising approximately 45.72% omega-3. This contrasts with Sargassum polycystum and Caulerpa lentillifera, which contain 9.63% and 7.55% omega-3, respectively (Matanjun et al. 2009). Given these findings, along with similar research, it is evident that numerous macroalgae are rich in n-3 fatty acids (Polat 2013; Tanna & Mishra 2018). Consequently, incorporating algae into the diet may positively affect blood lipid composition and help in preventing cardiovascular diseases such as arteriosclerosis (Erkkila et al. 2000).
In addition to their beneficial lipid profile, seaweed's protein content is also significant. Amid increasing health concerns related to meat consumption, there is a noticeable trend towards plant-based and vegetarian diets (Lang 2020). In this context, seaweeds emerge as a viable alternative, providing a rich and unique protein source (Espinosa-Ramírez 2023). Research shows that red algae, in comparison to green and brown varieties, have a higher protein content, with levels ranging from 19 to 47% of dry weight (Echave et al. 2021; De Souza 2023). In some cases, the protein concentrations in these red algae are either comparable to or exceed those found in traditional plant proteins from legumes (20–30%), cereals (10–15%), and nuts (20–30%) (De Souza 2023; Espinosa-Ramírez 2023).
Seaweed's potential to enhance dietary protein intake aligns with sustainability principles and could lead to significant changes in dietary habits (Echave et al. 2021). However, integrating seaweed proteins into mainstream diets faces the challenge of their bioavailability, which often appears lower than that of benchmark proteins like casein found in milk. This assessment comes from in vitro models that use digestive enzymes (Arasaki et al. 1984; Wells 2017). Despite these challenges, the protein potential of seaweed is promising and warrants further detailed study.
Seaweeds are rich in minerals, boasting a mineral content that is 10 to 20 times greater than terrestrial plants, and can constitute 20–50% of their dry weight in some cases (Muñoz 2020; Holdt & Kraan 2010; Pereira 2011; Piñeiro 2012; Rubio et al. 2017). For instance, species like Himanthalia elongata (sea spaghetti) contain more iron than Lens esculenta (lentils), and species such as Undaria pinnatifida (wakame) and Chondrus crispus (Irish moss) have calcium levels that surpass those in milk (Pereira 2011). However, the bioavailability of these nutrients warrants further investigation. Macroalgae are also rich in calcium, iron, magnesium, and iodine (Freitas et al. 2021). While there is concern that excessive consumption of iodine-rich algae could lead to hyperthyroidism, for most people, algae are not the primary dietary source of iodine (Smyth 2021). At standard servings, such as 4g of dry algae, iodine levels do not pose a significant health risk, as exceeding the recommended daily intake for adults (1100 µg/day) would require consuming an excessively large amount, approximately 286 g/day (Darias-Rosales et al. 2020).
Finally, further studies are necessary to explore the variation in algae's nutritional content, considering ecological factors that can significantly impact their nutritional value. These factors include the species of algae being cultivated, geographical regions, seasonal changes, harvesting effects, storage, and processing techniques (Wells 2017). For example, the mineral content in algae can vary with seasonal and environmental changes (Holdt & Kraan 2011; Rubio et al. 2017). In Norway, species like Saccharina latissima, Laminaria spp., and Alaria esculenta show lower ash content in the months of September, October, and November and higher content during spring, from February to June (Haug & Jensen 1954). Lighting conditions also affect their fatty acid profile (Hotimchenko 2002). Advancing our understanding of the nutritional composition of different algal species and the factors that influence the bioavailability of their nutrients when consumed by humans is therefore crucial.
Potential Risks Associated with Contaminants
While seaweeds may offer valuable nutritional contributions, their regular consumption could also expose individuals to contaminants. A key characteristic of these organisms is their capacity to absorb metallic ions and organic compounds from their aquatic surroundings (Vidotti 2004). Understanding the human health effects of ingesting heavy metals, which these organisms can bioaccumulate, is crucial and depends on how different species adapt to various, potentially contaminated environments.
Metals such as mercury, cadmium, copper, lead, and zinc represent the most common contaminants in biological products like algae (Arulkumar 2019). Recent research has found alarming levels of metals, radioactive isotopes, ammonia, dioxins, and pesticides in edible seaweeds (Spiegel et al. 2013; Rubio et al. 2017). However, consensus on the health risks posed by these contaminants is lacking, largely because their presence varies depending on the specifics of the seaweed's cultivation or extraction site. This variation has led the European Food Safety Authority (EFSA) to recommend conducting individualized analyses at national or regional levels, underscoring that contamination relates more to the growing environment than to the seaweeds themselves (EFSA 2005). For instance, a study on several brown algae species from Sri Lanka found low levels of arsenic, chromium, and cadmium, suggesting they are safe to eat (Makawita et al. 2020). Another study, examining eight species of red and brown algae from Asia and the European Union, found aluminum, cadmium, and lead levels within safe health limits according to European standards (Rubio et al. 2017). However, like other seafood, seasonal variations (Banach et al. 2020) and the potential lack of traceability regarding their origin and processing warn against unrestricted consumption.
Research has explored the potential for removing metals like copper, cadmium, and lead from algae during post-harvest processing (Tresnati et al. 2021). However, current research does not definitively determine the response of various algae species and metals to these cleaning methods, nor does it identify the most effective procedures for each unique scenario (Wells 2017). These unresolved issues pertaining to the food safety of algae consumption represent an additional obstacle to its promotion and, especially, to the regulation of its market (Araújo 2021).
Role of Socioeconomic and Psychological Variables of Consumers
Edible macroalgae, like other food groups, are chosen based on a variety of social, economic, cultural, and psychological factors (Freitas 2021). This review identifies education levels and food neophobia as significant factors influencing the consumption and avoidance of algae.
Specifically, we observed a positive correlation between years of schooling and algae consumption within modern food systems, as seen in Australia (Birch, 2019). This finding contrasts with what we observed in communities that follow traditional food systems, which are practices inherited across generations. In these communities, people usually reside in rural areas and rely on seasonal foods for personal consumption or for sale in informal markets (HLPE 2017). Our review indicates that there does not appear to be a significant relationship between education levels and seaweed consumption within these traditional systems. However, we propose the possibility of an inverse relationship, where higher levels of formal education are associated with lower knowledge and usage of such resources, including plants (Mcdade et al. 2007). This phenomenon might occur because educational curriculums, even those tailored for these populations, often neglect the cultural aspects of traditional communities (Mcdade et al. 2007). Nevertheless, due to the limited scope of research on seaweed, this hypothesis remains speculative at this stage.
The literature indicates that food neophobia negatively affects consumer interest in edible seaweeds. Defined as the fear or reluctance to try new foods, food neophobia leads to an aversion to the unfamiliar, influencing dietary choices (Jomori 2008). The introduction of unfamiliar products like seaweeds often elicits reactions of disgust, commonly known as the 'yuck factor' (Pluhar 2010; Verbeke et al. 2005). These findings suggest that simply highlighting seaweeds as healthy and sustainable may not effectively change the attitudes of consumers who view seaweed as an unfamiliar food. According to the COM-B model of behavioral change, capability, opportunity, and motivation are three critical elements that can facilitate behavioral change. Capability involves an individual's psychological and physical capacity to undertake an activity, opportunity refers to the external circumstances that enable a behavior, and motivation includes the cognitive processes that guide and encourage behavior (Michie 2011). Therefore, while the idea of consuming seaweeds might appeal to those aiming for healthier and more sustainable diets, overcoming psychological barriers to change remains a significant challenge.
Palmieri's study (2023) discovered that older respondents showed less willingness to try new foods, aligning with other research that suggests younger individuals tend to have lower levels of food neophobia (Loewen & Pliner 2000; Tuorila et al., 2001). Therefore, age appears to be another factor that, together with neophobia, enhances the tendency to reject new foods, including algae (Onwezen et al. 2021; Torri et al. 2020).
Moreover, the methods of food preparation and the combinations in which food is presented can significantly improve consumer attitudes (Kröger et al. 2022; Torri et al. 2020; Tuccillo et al. 2020). For example, seaweed offers a variety of consumption methods, such as being eaten fresh, dried, cooked, fried, dehydrated, flaked, powdered, and toasted (Batoréu 2005; Butcher 2020; Chapman et al. 2015; Lucas 2019; Mouritsen 2013; Tiitii 2022). Additionally, its recognized nutritional benefits lead to its incorporation in products like biscuits, yogurts, dairy, and bakery items (Moss 2021; Mohammad et al. 2019). The diversity in seaweed preparation and its culinary adaptability, along with its nutritional advantages, can play a role in diminishing food neophobia. This could make the process of adopting these foods less daunting and more gradual for those who are unfamiliar with them.