*3.4. Integrity of Gut Barrier*

Dysregulation of intestinal mucosal barrier function and loss of integrity of the gut barrier can increase the passage to the intestinal pathogens and endotoxins, which cause infection or inflammation [46]. Animal models have provided evidence linking gut barrier dysfunction, activation of inflammation signaling pathways, and progression of insulin resistance to type 2 diabetes [47]. The potential of *Ecklonia radiata*, a brown seaweed from New Zealand, and its polysaccharides (fucoidan and alginate) were reported to improve gut health in a rat model by increasing stool bulk, short-chain fatty acids, and butyrate production [48]. However, Michiels et al. [49] showed no effect of a dried extract of *Ascophyllum nodosum* on gut microbiota in piglets. To our best knowledge, no studies have addressed the impact of brown seaweed on the health and integrity of the gut barrier in humans. In the context of our study, no effect of our brown seaweed extract was observed on LBP, an acute-phase protein secreted by the liver in the bloodstream in response to a bacterial infection, and zonulin, a protein associated with a loss of intestinal barrier function that modulates the permeability of tight junctions between cells of the wall of the digestive tract. Further studies measuring various parameters of gut integrity, such as occludin, claudins, or mucin, in addition to LBP and zonulin, are necessary to determine the impact of brown seaweed and their extracts on gut integrity among people at risk of type 2 diabetes.

The results of the present study showed a marginal beneficial impact of a polyphenolrich extract obtained from two algae, *Ascophyllum nodosum* and *Fucus vesiculosus*, in the context of moderate weight loss over 12 weeks on metabolic risk factors of type 2 diabetes and cardiovascular disease, namely glucose homeostasis, heart rate, and Il-6 in prediabetic subjects. Moreover, our results should be interpreted with caution, given certain limitations. On the one hand, diet and physical activity were not strictly controlled, but on the other hand, our experimental approach was closer to the real context. Furthermore, we used 2 h OGTT instead of 3 h OGTT, which could have minimized the real effect of brown seaweed extract on glycemia, insulin, and C-peptide during OGTT. Finally, it might be worthwhile in subsequent studies to extend the duration of the trial to 6 months.

We acknowledge that this discussion has been focused on phlorotannins and fucoidans due to their known bioactive properties, but the extract contains other compounds such as small saccharides (mono- and disaccharide) as well as oligo- and polysaccharides, fatty acids, and phenolic compounds, as measured by Gabbia et al. [18]. For instance, the polysaccharide-rich composition of brown algae has shown the potential to act as prebiotics and to positively modulate the gut microbiota [50]. Moreover, in addition to phlorotannins, there are other polyphenolic compounds such as phenolic acids, flavonoids, phenolic terpenoids, and bromophenols in brown seaweeds, as reported by Cotas et al. [51]. On their own, each of these compounds can exhibit significant biological properties, including antidiabetic, anti-inflammatory, and antioxidant activities [51], and could potentially affect the parameters measured in this study. However, compared to phlorotannins, less is known about those polyphenols due to a lack of their characterization, isolation, and specific bioactivity analysis. Furthermore, it is possible that when combined, these compounds have interactions with each other, depending on the type and structure of these compounds, thereby modulating their effects.

In conclusion, the present results indicate that the consumption of a brown seaweed extract of *Ascophyllum nodosum* and *Fucus vesiculosus* for 12 weeks had no effect on body weight and blood glucose but induced a marginal beneficial impact on insulin secretion, heart rate, and Il-6 in overweight/obese prediabetic subjects. These results suggest that early attenuation of the inflammatory response by 500 mg of brown seaweed extract in the context of moderate weight loss could be associated with modest changes in metabolic parameters related to the prevention of type 2 diabetes. More studies with different doses and intervention durations are needed to determine the effects of this supplement on cardiovascular and type 2 diabetes risk factors.
