Seaweed has for many years been hailed as a healthy food due to its rich mineral content, especially as a source of iodine. It is also highly versatile – in its dried form, it can be an easy grab-and-go snack, an essential ingredient in Asian cuisine, such as sushi, onigiri (Japanese rice balls), kimbap (Korean sushi rolls), or even as a topping for congee and rice. According to the Consumer Council’s latest test on 27 ready-to-eat seaweed samples, all samples were found with a high iodine content, which could help maintain metabolism when consumed in moderation, but could affect thyroid functions with excessive intake. In particular, amongst the 4 samples labelled as suitable for infants and young children under 36 months old, 1 was found to have an iodine content per serving that exceeded the daily recommended nutrient intake (RNI) for infants and young children aged 1 to 3 by 90%. Parents are advised to pay extra heed when preparing meals with seaweed for their children.
At the same time, 70% (19 samples) were found to be “high-sodium” foods according to the standard set out by the Centre for Food Safety (CFS) (i.e. more than 600mg sodium per 100g solid food sample), while close to 40% (10 samples) were “high-fat” foods (i.e. more than 20g total fat per 100g food). As seaweed is often seen as tasty bite-sized snacks, it is easy to eat several servings at a time which would increase the risk of nutrients intake exceeding their respective upper limit, especially for infants and young children.
The 27 ready-to-eat seaweed samples included 18 seaweed snacks, 8 nori seaweed wrappers for sushi or onigiri, and 1 shredded seaweed sample, priced from $10.0 to $62.0 per pack, equivalent to a unit price of $40.6 to $386.7 per 100g, a difference of over 8 times. The seaweed snack sample with the highest unit price ($386.7 per 100g) only received an overall rating of 3.5 points, which was amongst the lowest. On the other hand, some of the samples with lower price receive a more satisfactory 4-point overall rating, once again evidencing that there are good quality yet affordable products on the market.
Amongst the samples, 4 seaweed snacks were labelled as suitable for infants and young children under 36 months old, thus were classified as foods for infants and young children. Test items included the nutrient content, and 6 types of metallic contaminants, while the nutrition labelling was also reviewed and compared against the test results.
All Samples Reached “Rich in Iodine” Levels
While 1 sample Exceeded Recommended Daily Intake Level for Adults
Iodine is an essential mineral for maintaining normal thyroid functions and metabolism in the human body, and for development of the brain, nervous system and body of infants. Severe iodine deficiency might lead to brain damage in foetuses or newborns, and could even impose risks of premature labour or miscarriages in pregnant women. On the other hand, prolonged excessive iodine intake could result in thyroid dysfunction, such as goitre, hyperthyroidism and hypothyroidism. The Council reminds consumers that as the human body cannot store huge amounts of iodine, it must be consumed in small amounts regularly.
Various types of human activity have led to climate change and caused ocean acidification. Based on a study in 2019, ocean acidification might increase the accumulated levels of iodine in seaweed, whereas seaweed native to different regions could also have drastically different iodine concentrations.
The test results revealed that all samples reached “rich in iodine” levels (not less than 45μg iodine per 100g solid food sample) set out in the “Food and Drugs (Composition and Labelling) Regulations” (“Labelling Regulations”), with iodine contents per 100g ranging from 1,030μg to 34,600μg, equivalent to 10μg to 450μg per suggested serving size. When consumed in appropriate amounts, they could help prevent iodine deficiency.
The highest iodine content per 100g was found in a sample of nori seaweed for rice balls (34,600μg). Consumption of 1 suggested serving (1.3g) would amount to an iodine intake of 450μg, which is higher than the daily RNI of iodine for adults (120μg), and equivalent to 75% of the tolerable upper intake level (UL) (600μg/day) set by the Chinese Nutrition Society (CNS). Upon consumption of 2 servings of the above sample (2.6g), the iodine intake would exceed the daily UL for adults recommended by the CNS while reaching 50% of that recommended by the World Health Organization (WHO) (not more than 30μg iodine per kg body weight, i.e. 1,800μg for a 60kg adult). As such, consumers should be mindful of the content per serving size so as to prevent excessive iodine intake.
1 Sample for Infants and Toddlers Exceeded Upper Intake Level of Iodine with 2 Servings
In particular, parents should pay extra heed to the seaweed consumption size by infants and young children, as they have a lower UL of iodine as compared with adults. For the 4 samples labelled as suitable for infants and young children under 36 months old, the iodine content per suggested serving ranged from 51μg to 171μg, of which the sample with the highest iodine content (171μg per serving) exceeded the RNI for young children aged 1 to 3 by 90%. Referencing the UL for young children set by CNS, Australia and New Zealand, consuming 2 servings (i.e. 2 packets, total 4g) of the aforementioned sample with the highest iodine content would incur an iodine intake of 342μg, which exceeded the daily iodine UL for children aged 1 to 10.
Aside from seaweed, a number of foods in the daily diet are already rich in iodine, such as saltwater fish, seafood (prawns, oysters, clams, etc.), eggs, milk and dairy products. Taking for example a daily menu with an egg (around 63g) for breakfast, 2 onigiri rice balls for lunch (each using 1 piece of 1g seaweed), an afternoon snack of skim milk (250ml), and a portion of golden threadfin bream (40g uncooked, around the size of a table tennis ball) for dinner, the total iodine intake would add up to around 172μg, equivalent to 191% of the RNI and 86% of the UL for a 4 to 6-year-old child. With this in mind, parents should pay attention to the serving size of seaweed as well as other iodine-rich ingredients when preparing meals for their children.
High-sodium and High-fat Dietary Traps Cannot be Ignored
As seaweed naturally contains salt, its sodium content would be even higher if salt is added during the manufacturing process. Excessive sodium intake over a prolonged period would increase the risks of high blood pressure and cardiovascular diseases.
In the test, 70% (19 samples) were found to reach the high-sodium food levels as defined by the CFS, with detected sodium content per 100g ranging from 614mg to 4,840mg. In the snack category, the sample with the highest sodium content per 100g (2,960mg) translated to a sodium intake of 89mg per serving (3g). While this only accounted for 4% of the daily maximum level of intake for adults as recommended by the WHO (less than 2,000mg), if one consumes the whole box of 9 pieces (3g/piece; total 27g), the sodium intake would amount to 799mg, equivalent to 40% of the daily maximum intake for adults.
In terms of the non-snack category, the sample with the highest sodium content (per 100g) was found with 4,840mg sodium. Despite its sodium intake (around 63mg) per serving (1.3g) merely accounting for 3% of the maximum intake for adults, the implication would be much greater for children. Assuming that a parent prepares onigiri for their child using 2 pieces of this seaweed sample, the seaweed alone would incur a sodium intake (126mg) equivalent to 11% of the proposed intakes for preventing non-communicable chronic diseases (PI-NCD) for children aged 4 to 6 recommended by the CNS. If the onigiri also contained other high-sodium ingredients, such as sauces, luncheon meat, etc., it would greatly increase the sodium intake of the child.
Meanwhile, in terms of the fat content, 10 samples (37%) were “high-fat” foods, with fat content per 100g ranging from 29.1g to 60.4g. Amongst these, the sample with the highest fat content (60.4g) was the highest across the total fat, saturated fatty acid and trans fatty acid contents per 100g. While it is easy to assume that seaweed, with their light and relatively dry texture, would not be high in fat, novelty varieties of seaweed snacks, such as those fried and heavily seasoned, its fat level cannot be undermined.
Metallic Contaminants Within Safety Limits but Nutrition Labelling Demands Improvement
6 types of metallic contaminants, namely cadmium, lead, chromium, total mercury, inorganic arsenic, and antimony, were tested. All 27 samples were detected with 2 to 5 types of metallic contaminants, with cadmium and inorganic arsenic, a human carcinogen, being the most common metallic contaminants, both found in all 27 samples, while antimony was not detected in any of the samples. Nevertheless, with reference to the respective maximum level, tolerable intake or provisional tolerable intake set out in Hong Kong, the Mainland, European Union and international committee for each type of metallic contaminant, the detected amounts of all metallic contaminants in the samples did not exceed the respective standards, and would probably not pose health risks when consumed in regular portions.
Aside from 4 samples which could not be directly compared, the rest were found with discrepancies between the declared and detected contents of 1 or more nutrients that did not comply with the requirements set out in the “Technical Guidance Notes on Nutrition Labelling and Nutrition Claims” (“Technical Guidance Notes”) by the CFS. The information of all relevant samples has been referred to the CFS for follow-up. As it is a fundamental right of consumers to receive accurate product information, the Council recommends manufacturers to promptly review and rectify their food labelling information to allow consumers to make informed choices.
Furthermore, despite the iodine content not being mandated for prepackaged foods according to the Labelling Regulations, in view of the large variance in iodine content amongst the seaweed samples (1,030μg to 34,600μg per 100g, a considerable variance of almost 33 times), the Council recommends manufacturers to include such information in the nutrition labels of their products for consumers’ reference, especially for seaweed products intended for consumption by infants and young children.
Consumption Tips on Ready-to-eat Seaweed:
- Carefully read the list of ingredients and nutrition label on seaweed products and be mindful of the sodium, fat and sugar intake levels. Consumers are recommended to select varieties of original flavour or with less seasoning;
- As seaweed snacks are light, airy and tasty, consumers should be mindful of unintentionally consuming more than the recommended portion;
- The Council reminds consumers that taste preferences are established in infancy and early childhood. If infants and young children are regularly fed "strong-tasting" foods, such as those high in sodium, they may develop a preference for salty foods in adulthood;
- While all the samples were "high-protein" (not less than 12g protein per 100g solid food sample) and "high-fibre" (not less than 6g dietary fibre per 100g solid food sample) foods, they should not be treated as the main source of protein and fibre;
- As recommended by the Hong Kong Dietitians Association, if consumers have symptoms such as a swollen thyroid suspected to be caused by excessive iodine intake, they should seek medical advice as soon as possible. Moreover, individuals with chronic kidney diseases or patients taking warfarin (a type of medication to help prevent blood clots) should consult with doctors or dietitians before consuming seaweed.
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