food australia Journal, Vol. 74 (1) January - March 2022

The anti-obesity potential of ulvan from the green seaweed Ulva

Words by Dr Jessica Pahl

The prolific green seaweed Ulva is an edible sea lettuce well-known for the formation of ‘green tides’ owing to rapid growth rates and broad environmental tolerance. However, the same properties that enable species of Ulva to form green tides are highly suitable for cultivation and this has been demonstrated in land-based cultivation in South Africa for abalone feedstock.(1) In addition to being a sustainable food source, Ulva contains commercially valuable bioactive compounds that have potential for the treatment of metabolic syndrome. Metabolic syndrome is the term used to describe the co-occurrence of abdominal obesity, high blood pressure, and high concentrations of glucose, cholesterol, and triglycerides in the bloodstream. Rates of obesity are increasing worldwide, and consequently the prevalence of metabolic syndrome is also increasing and with it a greater risk of developing type 2 diabetes and cardiovascular disease.

There are many factors at play that lead to this increased risk of metabolic syndrome and related conditions, but one potentially modifiable factor is the gut microbiome. The human gastrointestinal tract is colonised by up to 10 trillion microbes and the diversity and prevalence of certain species can indicate whether a gut microbiome is ‘healthy’ or implicated in disease. A gut microbiome that has decreased diversity, loss of beneficial organisms or irregular bacteria blooms has been linked to the development of various diseases.(2) The factors leading to this are not completely understood, however, genetic factors and a diet high in saturated fats and simple carbohydrates but low in dietary fibre are believed to have a causative role.(3)

Ulva contains a unique soluble fibre called ulvan (12% of the dry biomass), which is resistant to human enzymatic digestion and could therefore potentially exert prebiotic effects to confer beneficial changes to the composition and/or activity of the gut microbiome. We tested ulvan using an established 16-week model in rats, whereby a high-carbohydrate, high-fat diet was fed for the first eight weeks to induce obesity. In the remaining eight weeks of the study, the rats continued to consume the high carbohydrate, high-fat diet, but with an additional 0.5% of ulvan mixed into the food (an intake of approximately230 mg/kg body weight of the rat/day). The changes to body weight, body composition, blood pressure, glucose tolerance and the gut microbiome was tracked from start to finish of consuming ulvan in the diet.

In our study, ulvan slowed the progression of obesity by lowering body weight gain by 29% and fat mass gain by 45%. This anti-obesity effect was correlated with a 25% reduction in feed efficiency and a change in the gut microbiome towards one more associated with a lean phenotype, showing that ulvan potentially is an effective prebiotic. Ulvan was unable to reduce systolic blood pressure, blood cholesterol and triglycerides, and oral glucose tolerance. Further research of the health benefits of ulvan and to discover other uses of Ulva, for example the high lipid and protein yield in comparison to traditional crops, (4) would encourage the cultivation and commercial production of Ulva products in Australia, thus fully utilising a seaweed that is sustainable and native to the Australian coastline.

References

1. Bolton, J.J.; Robertson-Andersson, D.V.; Shuuluka, D.; Kandjengo, L. Growing Ulva (Chlorophyta) in integrated systems as a commercial crop for abalone feed in South Africa: a SWOT analysis. Journal of Applied Phycology 2009, 21, 575-583, doi:10.1007/s10811- 008-9385-6.

2. Dabke, K.; Hendrick, G.; Devkota, S. The gut microbiome and metabolic syndrome. Journal of Clinical Investigation 2019, 129, 4050-4057, doi:10.1172/JCI129194.

3. DeGruttola, A.K.; Low, D.; Mizoguchi, A.; Mizoguchi, E. Current understanding of dysbiosis in disease in human and animal models. Inflammatory Bowel Diseases 2016, 22, 1137-1150, doi:10.1097/MIB.0000000000000750.

4. Mata, L.; Magnusson, M.; Paul, N.A.; de Nys, R. The intensive land-based production of the green seaweeds Derbesia tenuissima and Ulva ohnoi: biomass and bioproducts. Journal of Applied Phycology 2016, 28, 365-375, doi:10.1007/s10811-015-0561-1.

Dr Jessica Pahl is a researcher at the University of Southern Queensland and was runner-up of the Judge’s Award at the AIFST 2021 Research Poster Competition. Email: jessica.pahl@usq.edu.au

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