Polyphenol-rich seaweed extracts may have anti-diabetic effects: Study
By Nathan Gray, 25-Nov-2010

Related topics: Research, Antioxidants, carotenoids, Cancer risk reduction, Diabetes

Polyphenol-rich extracts from edible seaweed may have anti-diabetic effects due to their ability to inhibit certain digestive enzymes, according to new research.
The study, published in Food Chemistry, suggests that the phenolic-rich extracts from four species of commonly found edible seaweed may possess the capacity to inhibit digestive enzymes as well as having potential to inhibit colon cancer.

“This paper outlines potential biological activities of polyphenols from edible seaweeds and, in particular, suggests that phlorotannin components of Ascophyllum nodosum have potential anti-diabetic effects through the inhibition of both alpha-amylase and alpha-glucosidase,” wrote the researchers, led by Felix Nwosu, from the University of Abertay Dundee, in partnership with the Scottish Crop Research Institute (SCRI)

Seaweed phenolics

Edible marine macroalgae, such as seaweeds form an important part of the diet in many far Eastern countries, whilst they are less used as foods in Western countries, their use is well documented.

Apart from food uses, including their main industrial use as thickeners and gelling agents, seaweeds are widely used as ingredients in cosmetics and as fertilizers.

However, edible seaweeds contain a range of components which have been suggested to have potential health benefits. They are good sources of dietary fibre, especially soluble fibre such as alginates, which can influence satiety and glucose uptake from foods – These soluble polysaccharides may also act as prebiotics, stimulating growth of beneficial bacteria in the colon.

The authors stated that as well as being sources of polyunsaturated fatty acids, minerals and certain vitamins, “edible seaweeds can contain appreciable amounts of polyphenols, which are effective antioxidants and may have particular biological activities.”

“For example, polyphenol-rich extracts and isolated phlorotannin components have been shown to inhibit proliferation of cancer cells and to influence anti-inflammatory responses,” wrote the researchers.

Nwosu and colleagues reported that recent, but limited, information suggests that polyphenol rich extracts from edible seaweeds have potential anti-diabetic effects through the modulation of glucose-induced oxidative stress, and inhibition of starch-digestive enzymes such as alpha-amylase and alpha-glucosidase.

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In the new study, phenolic-rich extracts from four edible marine macroalgae commonly found in U.K. waters (Ulva, Ascophyllum, Alaria, and Palmaria) were tested for their potential biological effects towards cultured colon cancer cells and for their ability to inhibit digestive enzymes to achieve potential anti-diabetic effects.

Effective extracts

The authors reported that all of the polyphenolic-rich extracts from the seaweeds inhibited proliferation of cultured colon cancer cells, observing that Alaria extracts were the most effective.

They found extracts from Palmaria, Ascophyllum and Alaria, but not Ulva, gave “reasonable recoveries of phenolics and inhibited the proliferation of colon cancer cells in a dose responsive manner.”

Extracts from Palmaria, Ascophyllum and Alaria all were all also found to inhibit alpha-amylase, whilst Ascophyllum extracts were observed to inhibit alpha-glucosidase, the other key enzyme involved in starch digestion and blood glucose regulation.

Achievable levels

Nwosu and co workers concluded that the seaweed extracts have the capacity to inhibit alpha-amylase and alpha-glucosidase activities “at levels which are easily achievable in the gut.”

They said that further research, to identify the active ingredients responsible for these effects is needed, noting that their findings may support and explain the anti-diabetic properties associated with algal extracts and algal phenolics in various in vivo studies.

Source: Food Chemistry
Published online ahead of print, doi:
“Anti-proliferative and potential anti-diabetic effects of phenolic-rich extracts from edible marine algae”
Authors: F. Nwosu, J. Morris, V.A. Lund, D. Stewart, H.A. Ross, G.J. McDougall