Type 2 diabetes mellitus is a chronic metabolic disorder. The morbidity of the world population attributable to diabetes is expected to increase from 415 million in 2015 to 642 million by 2040 [13]. The number of people with diabetes is increasing due to population growth, aging, urbanization, obesity, and physical inactivity [1], and refined carbohydrates, including rice and noodles have been implicated in the deterioration of glucose metabolism [14]. However, rice and noodles are major staple foods of Asian people such as the Chinese, Korean, and Japanese. Therefore, we have developed LS-HDF noodles containing okara and konjac for those who consume noodles regularly. In this study, we demonstrated the effect of LS-HDF noodles on glycemic response in healthy humans as a cross-over trial for the first time.
In a previous study, we investigated the effect of LS-HDF noodles intake on blood glucose levels in healthy ICR mice compared with that of commercial wheat noodles intake and reported that the increase in postprandial blood glucose levels was significantly suppressed after consumption of LS-HDF noodles [10]. In this study, postprandial blood glucose levels of the LS-HDF noodles group remained stable for 120 min after consumption of LS-HDF noodles. This result was almost similar to that of our previous data on mice; however, the difference in postprandial blood glucose levels between healthy humans who consumed wheat noodles and LS-HDF noodles was increased compared with that of healthy mice. The postprandial blood insulin levels of the LS-HDF noodles group remained stable for 120 min after intake of LS-HDF noodles. Accili et al. reported that not only hypoinsulinemia, but also hyperinsulinemia was harmful for body functions [15]. In particular, high levels of insulin levels in otherwise metabolically healthy persons are assumed to pose a risk factor towards the development of obesity [16, 17]. To prevent obesity in healthy individuals, it is important to suppress the increase in insulin levels. Therefore, we thought that LS-HDF noodles might be effective to prevent obesity. In addition, it is crucial to prevent metabolic syndrome diseases such as hyperglycemia and hyperlipidemia [18]. To reduce the number of individuals suffering from such diseases, it is necessary to develop processed foods that do not stimulate an increase in postprandial blood glucose levels and secretion of insulin [19]. Taking these reports into account, it can be suggested that LCDs such as LS-HDF noodles might be effective in protecting against metabolic syndrome diseases.
In the present study, we investigated the effect of LS-HDF noodles on glycemic response in healthy humans using a single meal test. In a previous study, we had demonstrated the effect of LS-HDF noodles on blood glucose levels in Spontaneously Diabetic Torii fatty rats, a model for obese type 2 diabetes, using a one-month test (28 days administration) and reported that the levels of blood glucose, HbA1c, and glycated albumin levels of the LS-HDF noodles group were significantly lower than those of control group [12]. In our study, after administration of LS-HDF noodles for 28 days, an oral glucose tolerance test (OGTT) indicated that blood glucose levels of the LS-HDF noodles group were significantly lower than those of control group. From this result, we could predict that intake of LS-HDF noodles might be effective for preventing type 2 diabetes in humans. There are benefits and risks of an LCD in type 2 diabetes patients; LCD increases mineral deficiency and hypovitaminosis and reduces dietary fiber intake [20, 21]. The dietary fiber levels were 11.3 g in the LS-HDF noodles used in this study (180 g). This indicates that LS-HDF noodles can replenish dietary fiber in LCDs, and LS-HDF noodles showed antioxidant activity in vitro [12]. Soy residues “okara” which contained a by-product obtained following the processing of soybeans is one of main ingredients in LS-HDF noodles. Okara is only soy residue, even though, it is rich in nutrients. In generally known, okara dry matter contains the insoluble fiber [22], protein [23], lipid [24] and isoflavones [25]. Especially, approximately 40–60% insoluble fiber (cellulose and hemicellulose) is contained in dried okara. Moreover, Vital et al. reported that phenolic compounds and flavonoids which showed antioxidant activities was contained in okara [26]. Furthermore, in our previous reports, we investigated that okara and fermented okara with Rhizopus oligosporus showed the reactive oxygen scavenging activity [27–28]. Konjac is one of main ingredients in LS-HDF noodles as well as okara. Konjac contained the konjac glucomannan, is water soluble polysaccharide [29]. Zhao et al. carried out the in vivo antioxidant and anti-inflammatory effects of konjac glucomannan in type 2 diabetic rats [30]. Therefore, we expect that the LS-HDF noodles which have the antioxidant activities might be effective for protecting against type 2 diabetes mellitus.