Effects of Sweeteners on the Gut Microbiota: A Review of Experimental Studies and Clinical Trials

The consumption of sugar-free foods is growing because of their low-calorie content and the health concerns about products with high sugar content. Sweeteners that are frequently several hundred thousand times sweeter than sucrose are being consumed as sugar substitutes. Although nonnutritive sweeteners (NNSs) are considered safe and well tolerated, their effects on glucose intolerance, the activation of sweet taste receptors, and alterations to the composition of the intestinal microbiota are controversial. This review critically discusses the evidence supporting the effects of NNSs, both synthetic sweeteners (acesulfame K, aspartame, cyclamate, saccharin, neotame, advantame, and sucralose) and natural sweeteners (NSs; thaumatin, steviol glucosides, monellin, neohesperidin dihydrochalcone, and glycyrrhizin) and nutritive sweeteners (polyols or sugar alcohols) on the composition of microbiota in the human gut. So far, only saccharin and sucralose (NNSs) and stevia (NS) change the composition of the gut microbiota. By definition, a prebiotic is a nondigestible food ingredient, but some polyols can be absorbed, at least partially, in the small intestine by passive diffusion: however, a number of them, such as isomaltose, maltitol, lactitol, and xylitol, can reach the large bowel and increase the numbers of bifidobacteria in humans. Further research on the effects of sweeteners on the composition of the human gut microbiome is necessary.

Effects of Probiotics and Synbiotics on Obesity, Insulin Resistance Syndrome, Type 2 Diabetes and Non-Alcoholic Fatty Liver Disease: A Review of Human Clinical Trials

The use of probiotics and synbiotics in the prevention and treatment of different disorders has dramatically increased over the last decade. Both probiotics and synbiotics are well known ingredients of functional foods and nutraceuticals and may provide beneficial health effects because they can influence the intestinal microbial ecology and immunity. The present study reviews the effects of probiotics and synbiotics on obesity, insulin resistance syndrome (IRS), type 2 diabetes (T2D) and non-alcoholic fatty liver disease (NAFLD) in human randomized clinical trials. Select probiotics and synbiotics provided beneficial effects in patients with obesity, mainly affecting the body mass index and fat mass. Some probiotics had beneficial effects on IRS, decreasing the cell adhesion molecule-1 levels, and the synbiotics decreased the insulin resistance and plasma lipid levels. Moreover, select probiotics improved the carbohydrate metabolism, fasting blood glucose, insulin sensitivity and antioxidant status and also reduced metabolic stress in subjects with T2D. Some probiotics and synbiotics improved the liver and metabolic parameters in patients with NAFLD. The oral intake of probiotics and synbiotics as co-adjuvants for the prevention and treatment of obesity, IRS, T2D and NAFLD is partially supported by the data shown in the present review. However, further studies are required to understand the precise mechanism of how probiotics and synbiotics affect these metabolic disorders.

Exogenous nucleosides modulate the expression of rat liver extracellular matrix genes in single cultures of primary hepatocytes and a liver stellate cell line and in their co-culture

BACKGROUND & AIMS

We have previously reported the antifibrotic effect of dietary nucleotides in cirrhotic rats. In this work, we used primary rat hepatocytes, a liver stellate cell line (CFSC-2G) and co-cultures of both cell types to investigate the effects of exogenous nucleosides on the gene expression of various extracellular matrix components and on markers of liver function, and to ascertain whether the effects found in vivo are due to CFSC-2G, hepatocytes, or are the consequence of cell-cell interactions.

RESULTS

Nucleosides enhanced fibronectin, laminin, and alpha1(I) procollagen levels in CFSC-2G and hepatocytes, as well as collagen synthesis and secretion in CFSC-2G. In contrast, nucleosides lowered fibronectin, laminin and alpha1(I) procollagen levels, and decreased collagen synthesis in co-cultures. Matrix metalloproteinase-13 content and collagen secretion increased in co-cultures incubated with nucleosides. Albumin increased in hepatocytes and co-cultures incubated in the presence of nucleosides.

CONCLUSIONS

Nucleosides modulate the production of extracellular matrix in single cultures of hepatocytes and of CFSC-2G, and in co-cultures. This effect seems to be regulated at the translational level. The opposite behavior of single cultures and co-cultures is probably due to the fact that the latter model reproduces many of the physical and functional relationships observed in vivo between hepatocytes and stellate cells.