# Current Research on the Effects of Non-Digestible Carbohydrates on Metabolic Disease
## 1 Introduction  
Metabolic disorders occur when the normal processes of macronutrients, such as proteins, carbohydrates, and lipids, in the human body are disrupted by various factors resulting in dysfunctions, including atherogenic dyslipidemia, insulin resistance, hypertension, and obesity [1]. Individuals with these dysfunctions are at high risk for developing metabolic diseases (MD), such as cardiovascular diseases (CVD) and diabetes [2], both of which are the most common cause of death globally [3]. The most important behavioral risk factors of MD are obesity, physical inactivity, and dietary habits [1]. In particular, several clinical trials and epidemiological studies suggest that dietary patterns characterized by high consumption of sugars, fat, and salt and low consumption of polyunsaturated fatty acids, vegetables, fruit, and fiber are strongly associated with a higher risk of MD [4]. Studies over the past decade using multiple genetic and diet-induced animal models have shown that insulin and leptin signaling cascades and the brain and its central nervous system are strongly involved in key metabolic signaling pathways of MD [5; 6; 7; 8; 9]. However, some of the mechanisms underlying the pathogenesis of MD are still unclear [10] and the use of drug therapies developed for the treatment of MD are also limited due to various side effects [11]. Therefore, physical activity, weight control, and diet control are very important to suppress the development of MD [12; 13; 14]. In particular, scientific evidence accumulated over the last few decades strongly suggests that balanced healthy diets rich in fruits, vegetables, legumes, whole grains, fish, nuts, and low-fat dairy products can decrease the risk of MD [15; 16]. Consumption of certain plants, seaweeds, and fermented food-derivedcompounds is known to have excellent health effects in preventing and suppressing the development of MD [17; 18]. Among these compounds, non-digestible carbohydrates (NDCs), mainly represented by resistant starch and dietary fiber, have received considerable attention as one of the most important components of MD development because of their numerous physiological advantages [19]. Many clinical and animal studies revealed that high intake of NDCs increased intestinal viscosity, fecal bulking, and production of short chain fatty acids (SCFAs) via gut fermentation, resulting in improving blood glucose, lipid, and insulin levels, reducing energy intake, and promoting satiety [19]. It was released that these physiological changes due to the high intake of NDCs were strongly correlated with suppression of the incidence of MD. Moreover, many meta-analysis results have confirmed the correlation between intake of NDCs and MD incidence [20]. However, their correlation was different according to the type, source, dose, and duration of NDC intake [21] and some of the mechanisms underlying the efficacy of NDCs on MD remain unclear.  
Therefore, the aim of this review is to discuss how NDCs regulate the incidence of MD, including obesity, diabetes, and CVD, by focusing on mechanisms by which the physical and fermentation properties of NDCs in the gastrointestinal (GI) system interfere with the absorption of MD risk-associated metabolites, increase satiety, and improve gut health.