# Current Research on the Effects of Non-Digestible Carbohydrates on Metabolic Disease
## 5 NDCs and MDs  
### Obesity  
Obesity, defined as a state of excess adiposity, is one of the most important risk factors for MD [52]. Obesity is related to the balance between energy intake and expenditure; thus, reducing energy intake and increasing energy expenditure are ways to control obesity. Energy intake is particularly associated with eating habits. Among various foods, a high intake of NDCs has a strong correlation with a reduction in obesity [53].  
Intake of NDCs interferes with the absorption of energy sources, including glucose and lipids, and with the accessibility of digestion enzymes to substrates in the intestine because of the viscous and fecal bulking properties of NDCs, although SCFAs produced from NDCs by gut microbiota are used as an energy source. Additionally, both properties can increase the gastric emptying time, resulting in an increase in satiety [54]. SCFAs can also stimulate satiety through the activation of satiety hormones, such as PYY and GLP-1, and energy-balancing hormones, such as leptin [55]. Consequently, energy intake can be reduced by the intake of NDCs, whereas the breakdown of stored energy sources, such as fat in the body, can be increased through energy production metabolism, including \(\beta\)-oxidation and the citric acid cycle, resulting in a reduction in obesity [56]. Therefore, intake of NDCs can reduce obesity and related disorders.  
The anti-obesity effects of pectin, \(\beta\)-glucan, psyllium, FOS, GOS, and non-fiber NDCs have been investigated (Table 2). Animal studies showed that fruit pectin intake showed anti-obesity effects by regulating the circulation of energy balancing hormones such as adiponectin, leptin, and ghrelin [57; 58; 59]. In particular, high-esterified pectin, a major component of soluble dietary fiber present in vegetables and fruits, was more effective in suppressing obesity than low-esterified pectin [60]. Intake of 2% barley \(\beta\)-glucan for 12 weeks or 10% FOS for 6 weeks also reduced body weight gain and fat mass in HFD-induced obese mice and increased secretion of gut hormones, PYY and GLP-1 in the plasma [61]. Moreover, mice fed with non-fiber soluble NDCs, such as malto-oligosaccharides (MOS 6 g/kg for 11 weeks), chitin oligosaccharides (COS 200 mg/kg for 21 weeks), and bovine-milk oligosaccharides (BMO, 6% BMO diet for 6 weeks) showed a reduction in BW, improved lipid profile, and increased glucose tolerance [62; 63; 64]. However, some studies have shown that the anti-obesity effect of NDCs differs according to their type and source. Mice fed with 10% (\(w/w\)) insoluble cereal fiber for 45 weeks had lower weight gain and improved insulin sensitivity compared with those fed with soluble guar fiber [65]. In a human study, the anti-obesity effects of pectin were also reported [66] as similar to the results of animal studies [57; 58; 59]. Psyllium husk has also been shown to have anti-obesity effects in obese humans [67], but there was no significant difference in almost all anthropometric measures in NAFLD patients consuming psyllium husk at 10 g/day for 12 weeks, except for the reduction in body weight and BMI [68]. FOS and GOS showed decreased hunger, desire to eat, energy intake, body weight, waist circumference, waist-to-height index, sagittal abdominal diameter, body fat, and serum TG levels in obese adults and children [69; 70; 71; 72]. To further explain the differences in the impact of NDCs on obesity according to the type and source of NDCs, other mechanisms, such as population and diversity of gut microbiota and their metabolites, including secondary bile acids, except for SCFAs, may be needed because many studies suggest that gut microbiota and secondary bile acids affected by high intake of NDCs are strongly related to obesity [39].