Nutritional properties of seaweeds
14 October 2016 • Author(s): Lynn Cornish, Seed Stock Manager, Acadian Seaplants Limited
The Webster’s Dictionary defines food as “a material consisting of protein, carbohydrate, and fat used in the body of an organism to sustain growth, repair, and vital processes, and to furnish energy”.
As such, the foods we eat affect our overall health, development, and well-being. Therefore, there is some irony in the fact that neurological diseases, particularly in developed countries, are on the rise1, with the economic costs of these estimated to be in the €798 billion range2. Such neuro-degenerative disorders include Alzheimer’s, dementia, Parkinson’s Disease, Multiple Sclerosis, and Huntington’s, among many others. Another sobering statistic around human health relates to cardiovascular diseases that remain the number one cause of death globally3. Indeed, the American Heart and Stroke Association reported in 2015 that approximately 2,150 Americans die each day from these diseases; that equates to one every 40 seconds4. While the reasons for these troubling statistics are both complicated and varied, food remains a fundamental component contributing to our overall health and wellness.
Seaweeds are a substantial source of prebiotic fibres, amongst other proven health benefits
From the provision of all the brain essential nutrients, to high fibre contents and robust antioxidant capacities, macroalgae (seaweeds) can play important roles in human health and nutrition. The only nutritional element seaweeds collectively lack – in terms of a food to ‘sustain growth, repair, and vital processes, and to furnish energy’ – is calories. In these troubling ‘obesogenic’ times, that is not a bad attribute; in fact it is an important factor regarding the contention that seaweeds are ideal candidates for improving the nutritional quality of manufactured foods5. In their role as an ancient and natural food resource, seaweeds remained important to only a relatively small number of global consumers; mostly in Asia and a scattering of coastal populations around the world. However, today science is enlightening the general public in regard to the nutritional and wellness benefits of this fascinating precursor to land plants. It is estimated, for example, that around nine million tonnes of farmed seaweeds were used for direct human consumption in 20126. Soon the expectation is that, in order to meet the demands of an ever increasingly educated public, food manufacturers will be formulating and producing a plethora of goods containing whole seaweeds and seaweed ingredients or extracts.
In terms of protein content, seaweeds can be an excellent source, although total amounts depend upon species and culture conditions. Dulse (Palmaria palmata), for example, can range between 8-35% protein and some nori species (Pyropia) have been shown to contain as much as 47% protein. The carbohydrate content of seaweeds is most significant in relation to the high proportion of soluble and insoluble fibres associated with them. These function both as important pre-biotic agents, enhancing gut health and improving bacterial populations, and by providing bulking effects, facilitating smooth passage through the gastrointestinal tract. The fat content of seaweeds is relatively low and mainly consists of lipids, or fatty acids. However, it is noteworthy that algae – both microalgae and macroalgae – are the rudimentary sources of the essential n-3 polyunsaturated fatty acids, docosahexanoic acid (DHA) and eicosapentaenoic acid (EPA). It is actually at this lower level of the food chain where those vital fatty acids are synthesised de novo, and they are then consumed and concentrated by fish and shellfish7,8. Significantly, the ratio of n-6 to n-3 in seaweeds (and fish) is approximately 1:1, very similar to the proportions of the fatty acids in the human brain. Disturbingly, the wide global availability of n-6 in our foods has skewed that important ratio such that, in the United States, for example, the ratio of n-6 to n-3 is actually in the vicinity of 20; in Denmark it is around eight; and in Mexico it is 25. The ideal is considered to be 1-59.
In addition to the macronutrients necessary for sustaining human growth and development, seaweeds also contain all the brain essential nutrients necessary for neural growth and protection, cognition, learning, and memory. This point is especially important with respect to maternal diets as brain development begins with the foetus and continues until approximately age two. Deficiencies in the neonate of vitamin B12, zinc, iodine, iron, or DHA, for example, can lead to impaired learning and poor cognitive development even later in life. Some seaweeds are viable sources of B12 and Pyropia is one of them, however only a small proportion of the over 10,000 seaweed species in the world have been adequately analysed for this essential vitamin, which can only be obtained from our diet. Also critical for human cognitive function and development, linking neuronal pathways and playing a pivotal role in learning and memory, is the transition metal, zinc. After iron, this is the most abundant metal nutrient in the body, and it is present in all tissues. Zinc is normally present in a minor plasma pool within the human body and it has a rapid turnover rate, such that a daily intake is required to achieve steady state and to maintain and support all the functions it is involved in. With their less diverse diets, many elderly people are also susceptible to zinc deficiencies, as this mineral is present in relatively small amounts in most foods. Good sources of zinc are certain cuts of meat, such as liver, oysters and crustaceans and, of course, seaweeds.
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