Obesity and NAFLD: The Role of Bacteria and Microbiota

This study investigated the inhibitory effects of super-comminuted dietary fiber from pomelo peel (SCPPDF) against high-fat diet (HFD)-induced obesity in mice. Mice were divided into five groups, which were fed with a normal diet, HFD, and HFD supplemented with low, medium, and high doses of SCPPDF for six weeks, respectively. Results showed that the SCPPDF supplementation effectively decreased the body weight and fat accumulation in liver and epididymal tissues in the HFD-fed mice, and decreased serum levels of triglycerides, low-density lipoprotein cholesterol, and total cholesterol. In addition, SCPPDF supplementation also decreased the Firmicutes to Bacteroidetes ratio (F/B), increased the relative abundances of short-chain fatty acids-producing bacteria, such as Lactobacillus, Bifidobacterium, and Allobaculum, reduced those of pathogenic bacteria, such as Staphylococcus and Corynebacterium_1, thereby regulating the HFD-induced imbalance of gut microbiota in mice. These findings indicated that SCPPDF could effectively inhibit obesity by regulating blood lipid levels, improving gut microbiota. SCPPDF has great potential to be developed into prebiotics or functional foods.

Nonpharmacological treatment in metabolic-associated fatty liver disease (MAFLD) consists of lifestyle interventions, mainly based on physical exercise and changes in dietary habits to slow the progression and improve the course of the disease. This chapter starts by introducing the liver response to lifestyle interventions in biochemical parameters, imaging tests, and histology. Next, we review the evidence to date and go in-depth into the study of how different dietary patterns, including the Mediterranean diet that has been the most studied diet in this disease, but also how different macro and micronutrients can influence the course of MAFLD. We also review the current evidence to date about the different models of exercise that have shown efficacy in slowing or stopping the progression of this disease. At the end of the chapter, we show our conclusions highlighting the most solid scientific evidence.

Non-alcoholic fatty liver disease (NAFLD), characterized by the accumulation of excessive intrahepatic fat, is a leading metabolic disorder also considered as the hepatic manifestation of metabolic syndrome (MS). Though more commonly observed in obese individuals and those with metabolic risk factors, it also develops in a considerable number of non-obese individuals as well as participants without having any component of MS. The basic mechanism involved in the development of fatty liver is the imbalance between lipid uptake, synthesis, and metabolism in the liver, normally controlled by several mechanisms to maintain lipid homeostasis. As a complex progressive liver disorder, the NAFLD pathogenesis is multifactorial, and several new pathogenic phenomena were discovered over time. The available literature suggests the role of both genetic and environmental factors and associated metabolic factors; however, the mechanism of progression is not completely understood. In this review, we discuss different pathogenic mechanisms and their interplay to provide an elaborate idea regarding NAFLD development and progression. Better understanding of pathogenic mechanisms will be useful in finding new treatment for patients with NAFLD.

Gut microbiota dysbiosis and oxidative stress may play important roles in the progression of nonalcoholic fatty liver disease (NAFLD). Fermented foods contain probiotics and other bioactive components that may improve gastrointestinal health and provide other health benefits. Here, we investigated the effect of Lactobacillus-fermented black barley on NAFLD rats. Adult Sprague Dawley rats were randomized into four groups: normal chow diet (NC), high-fat diet (HF), HF + fermented black barley treatment (HB) and HF + Lactobacillus treatment (HL). The rats in the HB and HL groups were continuously administered fermented black barley or Lactobacillus, respectively, for 12 weeks (1 mL/100 g·BW, containing 1 × 10⁸ CFU/mL Lactobacillus). Compared with the HF treatment, HB treatment effectively inhibited the increase in body weight, liver and abdominal fat indexes and hepatic lipids (p < 0.01), increased hepatic SOD activity (p < 0.05), decreased thiobarbituric acid reactive substances (TBARSs) (p < 0.01) and improved liver function. Moreover, Lactobacillus-fermented black barley exhibited regulatory effect on high-fat diet-induced intestinal microbiota dysbiosis by increasing the relative microbiota abundance and diversity, increasing the relative abundance of Bacteroidetes, decreasing the Firmicutes/Bacteroidetes ratio, increasing the abundances of some intestinal probiotics (such as Akkermansia and Lactococcus), and influencing some of the fecal metabolites related to hormones and lipid metabolism. The supplementation of fermented cereal food might be a new effective and safe preventive dietary strategy against NAFLD.

Recent evidence indicates the use of probiotics in the prevention and treatment of diseases. Probiotics are capable of changing the gut microbiota composition and bile acid synthesis to elicit health benefits such as cholesterol-lowering, weight reduction, and improving insulin sensitivity. The aging population is prone to develop diseases because of their decreased physiological and biological systems. Probiotics are one of the promising supplements that may potentially counteract these detrimental effects. This review will discuss the influence of probiotics on bile acids in different populations-the elderly, obese individuals, and those with hypercholesterolemia, type 2 diabetes, hypertension, and non-alcoholic fatty liver disease.