# Potential Prebiotic and Anti-Obesity Effects of _Codium fragile_ Extract
## 1 Introduction  
Marine algae are important sources of compounds with health-enhancing biological properties [1], including anti-inflammatory, anticancer, and immune enhancing functionalities [2; 3; 4; 5]. Marine algae contain large amounts of sulfated polysaccharides that can be used as prebiotics [6]. These polysaccharides are structurally atypical compared to terrestrial glycans and are resistant to gastric acid, gastrointestinal absorption and host digestive enzymes [7]. In addition, enzymatic hydrolysis of seaweed-derived carbohydrates and proteins promotes changes in physicochemical properties and enhances the efficacy of bioactivities such as antioxidant activity [8; 9]. Marine algae polysaccharides can be used as prebiotics for gut microbiota, which partially degrade them into other bioactive compounds, such as oligosaccharides and short chain fatty acids (SCFAs) acting as food sources for these organisms and allowing them to proliferate [10; 11; 12; 13; 14]. In addition to these polysaccharides, marine algae contain other bioactive compounds, such as polypeptides, polyphenols, and phytochemicals, which can be used as prebiotics. Despite their myriad of biologically active compounds, marine algae are predominantly consumed as food, processed with salt or seasoning. There is, therefore, scope for expanding the development of functional foods which contain various bioactive compounds derived from marine algae. _Codium fragile_ is a green alga used as a traditional food ingredient in Asia [15]. Green algae produce high amounts of sulfated polysaccharides including sulfated galactans, mannans, xylans, and ulvans. These sulfated polysaccharides are composed of galactose, rhamne, xylose, glucose, glucuronic acid and sulfates (and more rarely, mannose and arabinose) [6; 16]. Sulfated polysaccharides derived from green algae have shown various biological activities, including anti-viral, immune-stimulatory, and anticancer effects [17; 18; 19]. Obesity is a disorder involving excessive body fat, which increases the risk of many diseases, including diabetes, high blood pressure, and other cardiovascular complications. Marine algae consumption is associated with an anti-obesity activity affected by various mechanisms including alterations of lipid metabolism, inhibition of inflammation, suppression of adipocyte differentiation and delay in gastric emptying [5]. Marine algae are rich in dietary fiber, so they can be used as an anti-obesity ingredient. In addition, there are many reports of potential therapeutic effects of marine algae consumption in weight and obesity management. [20]. Ulvan from brown algae also lowers triglycerides, total cholesterol, and total lipid levels [21]. The anti-obesity activity of marine algae is associated with bioactive compounds, including polysaccharides, peptides, phlorotannins, and carotenoids [22]. Fucoxanthin is the most well studied marine algae bioactive compound displaying an anti-obesity effect [23]. Adipose tissue is a loose connective tissue composed mostly of adipocytes [24]. As an energy reservoir and endocrine organ, adipose tissue is known to play an important role in the regulation of energy metabolism for the human body through expression and secretion of an array of adipokines [25; 26]. Adipocyte differentiation, also called adipogenesis, is the process during which fibroblast-like preadipocytes develop into mature adipocytes [27]. 3T3-L1 cells, originally derived from mouse embryos, have served as a useful in vitro model for adipocyte differentiation and function [28]. Phlorotannin has been shown to strongly inhibit lipid accumulation in 3T3-L1 adipocytes [29], as well as inhibit adipocyte differentiation. Fucosterol has been reported to decrease the expression level of the adipocyte marker proteins PPAR and C/EBP. Marine algae may also prevent obesity by modifying relative amounts of different gut bacteria and polysaccharides and have been shown to repair the intestinal barrier and reduce inflammation [30].