Possible involvement of food texture in insulin resistance and energy metabolism in male rats

Eating behaviors and incidence of type 2 diabetes in Japanese people: The population-based Panasonic cohort study 15

AIM/INTRODUCTION

This historical cohort study sought to research the relationship between eating behaviors and the incidence of type 2 diabetes in a large, long-term cohort of Japanese subjects.

MATERIALS AND METHODS

Panasonic Corporation employees who had no history of diabetes and attended yearly health surveys between 2008 and 2018 were included in this study. The main outcome measure was diabetes onset.

RESULTS

This study included 128,594 participants and 6,729 participants who developed type 2 diabetes in the study period. Skipping breakfast, fast eating, snacking after dinner, and eating meals before sleeping were linked with the risk of the incidence of type 2 diabetes. In individuals with a BMI < 25 kg/m2, fast eating (hazard ratio [HR]: 1.61, 95% confidence interval [CI]: 1.37-1.90), and eating meals before sleeping (HR: 1.09, 95% CI: 1.02-1.17) were likewise associated with an increased risk of incident type 2 diabetes. Nevertheless, fast eating (HR: 1.08, 95% CI: 0.89-1.30) and meals before sleeping (HR: 0.94, 95% CI: 0.88-1.01) were not related to the occurrence of type 2 diabetes in individuals with a BMI ≥25 kg/m2 (P value for interaction = 0.0007 [fast eating] and 0.007 [meals before sleeping], respectively). No significant interaction effect between sex and eating behavior was found.

CONCLUSIONS

With respect to Japanese people, especially in people with a BMI < 25 kg/m2, eating behaviors may be a risk factor for the occurrence of type 2 diabetes.

Mechanism of muscle atrophy in a normal-weight rat model of type 2 diabetes established by using a soft-pellet diet

Dietary factors such as food texture affect feeding behavior and energy metabolism, potentially causing obesity and type 2 diabetes. We previously found that rats fed soft pellets (SPs) were neither hyperphagic nor overweight but demonstrated glucose intolerance, insulin resistance, and hyperplasia of pancreatic β-cells. In the present study, we investigated the mechanism of muscle atrophy in rats that had been fed SPs on a 3-h time-restricted feeding schedule for 24 weeks. As expected, the SP rats were normal weight; however, they developed insulin resistance, glucose intolerance, and fat accumulation. In addition, skeletal muscles of SP rats were histologically atrophic and demonstrated disrupted insulin signaling. Furthermore, we learned that the muscle atrophy of the SP rats developed via the IL-6-STAT3-SOCS3 and ubiquitin-proteasome pathways. Our data show that the dietary habit of consuming soft foods can lead to not only glucose intolerance or insulin resistance but also muscle atrophy.

Merkel cells and keratinocytes in oral mucosa are activated by mechanical stimulation

The detection of mechanical qualities of foodstuffs is essential for nutrient acquisition, evaluation of food freshness, and bolus formation during mastication. However, the mechanisms through which mechanosensitive cells in the oral cavity transmit mechanical information from the periphery to the brain are not well defined. We hypothesized Merkel cells, which are epithelial mechanoreceptors and important for pressure and texture sensing in the skin, can be mechanically activated in the oral cavity. Using live-cell calcium imaging, we recorded Merkel cell activity in ex vivo gingival and palatal preparations from mice in response to mechanical stimulation. Merkel cells responded with distinct temporal patterns and activation thresholds in a region-specific manner, with Merkel cells in the hard palate having a higher mean activation threshold than those in the gingiva. Unexpectedly, we found that oral keratinocytes were also activated by mechanical stimulation, even in the absence of Merkel cells. This indicates that mechanical stimulation of oral mucosa independently activates at least two subpopulations of epithelial cells. Finally, we found that oral Merkel cells contribute to preference for consuming oily emulsion. To our knowledge, these data represent the first functional study of Merkel-cell physiology and its role in flavor detection in the oral cavity.

Food texture affects glucose tolerance by altering pancreatic β-cell function in mice consuming high-fructose corn syrup

The incidence of metabolic diseases, such as type 2 diabetes, has increased steadily worldwide. Diet, beverages, and food texture can all markedly influence these metabolic disorders. However, the combined effects of food texture and beverages on energy metabolism remains unclear. In the present study, we examined the effect of food texture on energy metabolism in mice administered high-fructose corn syrup (HFCS). Mice were fed a soft or hard diet along with 4.2% HFCS or tap water. Body weight and total caloric intake were not affected by food texture irrespective of HFCS consumption. However, caloric intake from HFCS (i.e., drinking volume) and diet were higher and lower, respectively, in the hard food group than in the soft food group. The hard food group’s preference for HFCS was absent in case of mice treated with the μ-opioid receptor antagonist naltrexone. Despite increased HFCS consumption, blood glucose levels were lower in the hard-diet group than in the soft-diet group. In HFCS-fed mice, insulin levels after glucose stimulation and insulin content in the pancreas were higher in the hard food group than the soft food group, whereas insulin tolerance did not differ between the groups. These food texture-induced differences in glucose tolerance were not observed in mice fed tap water. Thus, food texture appears to affect glucose tolerance by influencing pancreatic β-cell function in HFCS-fed mice. These data shed light on the combined effects of eating habits and food texture on human health.

Fast eating is a strong risk factor for new-onset diabetes among the Japanese general population

Although many studies that have examined the relationship of type and amount of food and the frequency of eating with new onset of diabetes, there are few reports on the relationship between how meals are eaten, such as skipping breakfast, snacking or food ingestion speed, and the onset of diabetes. We investigated the relationship between eating speed, as well as other eating habits such as snacking and skip breakfast, and new onset of diabetes in a nation-wide Japanese cohort. We obtained data from the nation-wide annual health check program in Japan. In 197,825 participants without diabetes in 2008, questionnaires recorded data on the diet habits (eating speed, snack after supper or before sleep, and skipping breakfast) and unadjusted and multivariable-adjusted logistic regression models were used to measure the odds ratio of new-onset diabetes mellitus in a 3-year follow up. The proportion of fast eaters, those who snack after supper, snack before sleep, and skip breakfast was higher in the new-onset diabetes group than in the group who did not develop diabetes mellitus. As compared with the non-fast eater group, fast eaters were generally younger, had higher BMI, had more weight gain from 20 years onwards, and experienced frequent weight fluctuations of ≥3 kg within 1 year. The risk of fast eaters developing diabetes mellitus remained even after correction for multiple factors including age, body weight, rate of weight change, blood pressure, smoking, and alcohol consumption. No other eating habits were independent predictors for onset of diabetes mellitus. Results show that fast eating is a sole predisposing factor among eating habits for new-onset diabetes. Future studies were warranted to evaluate whether avoidance of fast eating is beneficial for prevention of diabetes mellitus.

Insight into miRNAs related with glucometabolic disorder

A microRNA (miRNA) is a single-stranded, small and non-coding RNA molecule that contains 20-25 nucleotides. More than 2000 miRNAs have been identified in human genes since the first miRNA was discovered in Caenorhabditis elegans in the early 1990s. miRNAs play a crucial role in various biological processes by regulating gene expression through post-transcriptional mechanisms. The alterations of their levels are associated with various diseases, such as glucometabolic disorder and lipid metabolism disorder. In recent years, miRNAs have been proved to be involved in regulating the functions of pancreatic β-cells, insulin resistance and other biological behaviors related to glucometabolic disorder and the pathogenesis of diabetes mellitus (DM). This review summarized specific miRNAs, including miRNA-375 (miR-375), miRNA-155 (miR-155), miRNA-21 (miR-21), miRNA-33 (miR-33), the let-7 family and some other miRNAs related to glucometabolic regulation, introduced the obstacles and challenges in miRNA therapy, and discussed the prospect of new treatment methods for glucometabolic disorder.

Theaflavins Improve Insulin Sensitivity through Regulating Mitochondrial Biosynthesis in Palmitic Acid-Induced HepG2 Cells

Theaflavins, the characteristic and bioactive polyphenols in black tea, possess the potential improving effects on insulin resistance-associated metabolic abnormalities, including obesity and type 2 diabetes mellitus. However, the related molecular mechanisms are still unclear. In this research, we investigated the protective effects of theaflavins against insulin resistance in HepG2 cells induced by palmitic acid. Theaflavins significantly increased glucose uptake of insulin-resistant cells at noncytotoxic doses. This activity was mediated by upregulating the total and membrane bound glucose transporter 4 protein expressions, increasing the phosphor-Akt (Ser473) level, and decreasing the phosphorylation of IRS-1 at Ser307. Moreover, theaflavins were found to enhance the mitochondrial DNA copy number, down-regulate the PGC-1β mRNA level and increase the PRC mRNA expression. Mdivi-1, a selective mitochondrial division inhibitor, could attenuate TFs-induced promotion of glucose uptake in insulin-resistant HepG2 cells. Taken together, these results suggested that theaflavins could improve hepatocellular insulin resistance induced by free fatty acids, at least partly through promoting mitochondrial biogenesis. Theaflavins are promising functional food ingredients and medicines for improving insulin resistance-related disorders.

Influence of food texture on energy metabolism and adiposity in male rats

NEW FINDINGS

What is the central question of this manuscript? What is the effect of food texture on fat accumulation, lipogenesis and proinflammatory factors in the adipose tissue and on energy balance in male rats? What is the main finding and its importance? Calorie intake and fat accumulation in rats fed soft pellets ad libitum increased, but their body weight did not. The data suggest that, even when BMI is normal, frequent consumption of soft food may contribute to the development of lifestyle-related diseases.

ABSTRACT

Dietary factors such as food texture are known to affect feeding behaviour and energy metabolism. We recently found that rats fed soft pellets (SPs) on a 3 h restricted feeding schedule showed glucose intolerance, insulin resistance with disruption of insulin signalling, and hyperplasia of pancreatic β-cells, even though there were no differences in energy intake and body weight between rats fed control pellets (CPs) and rats fed SPs. We investigated the effect of food texture on fat accumulation, lipogenesis and proinflammatory factors in the mesenteric fat, as well as on energy balance in male rats fed CPs or SPs. We used 7-week-old Wistar rats that were randomly divided into two groups, ad libitum fed either CPs or SPs for 27 weeks. Body weight and calorie intake were monitored once a week throughout the experiment. The calorie intake, lipogenesis and fat accumulation of the rats fed SPs increased, whereas their body weight did not. Additionally, SP rats used their fat mainly as a source of energy and increased their energy expenditure. Our data suggest that the habit of frequently eating soft food causes visceral fat accumulation without an increase in body weight. Further investigations using soft-textured foods could lead to the development of appropriate interventions for non-overweight patients with lifestyle-related diseases.

IRS-2 Partially Compensates for the Insulin Signal Defects in IRS-1-/- Mice Mediated by miR-33

Insulin signaling is coordinated by insulin receptor substrates (IRSs). Many insulin responses, especially for blood glucose metabolism, are mediated primarily through Irs-1 and Irs-2. Irs-1 knockout mice show growth retardation and insulin signaling defects, which can be compensated by other IRSs in vivo; however, the underlying mechanism is not clear. Here, we presented an Irs-1 truncated mutated mouse (Irs-1-/-) with growth retardation and subcutaneous adipocyte atrophy. Irs-1-/- mice exhibited mild insulin resistance, as demonstrated by the insulin tolerance test. Phosphatidylinositol 3-kinase (PI3K) activity and phosphorylated Protein Kinase B (PKB/AKT) expression were elevated in liver, skeletal muscle, and subcutaneous adipocytes in Irs-1 deficiency. In addition, the expression of IRS-2 and its phosphorylated version were clearly elevated in liver and skeletal muscle. With miRNA microarray analysis, we found miR-33 was down-regulated in bone marrow stromal cells (BMSCs) of Irs-1-/- mice, while its target gene Irs-2 was up-regulated in vitro studies. In addition, miR-33 was down-regulated in the presence of Irs-1 and which was up-regulated in fasting status. What's more, miR-33 restored its expression in re-feeding status. Meanwhile, miR-33 levels decreased and Irs-2 levels increased in liver, skeletal muscle, and subcutaneous adipocytes of Irs-1-/- mice. In primary cultured liver cells transfected with an miR-33 inhibitor, the expression of IRS-2, PI3K, and phosphorylated-AKT (p-AKT) increased while the opposite results were observed in the presence of an miR-33 mimic. Therefore, decreased miR-33 levels can up-regulate IRS-2 expression, which appears to compensate for the defects of the insulin signaling pathway in Irs-1 deficient mice.

The short-term effects of soft pellets on lipogenesis and insulin sensitivity in rats

The purpose of the present study was to investigate the short-term effects of a 12-day, soft pellet (SP) diet with a 3-h restricted feeding schedule on caloric intake, body weight, lipid metabolism, and insulin sensitivity. Glucose and insulin levels were measured pre-, mid-, and post-feeding. The SP rats exhibited postprandial hyperglycemia compared to rats fed control pellets (CP). The insulin response of SP rats during a meal was significantly higher than that of CP rats. There were no significant differences in the hepatic triacylglycerol contents and lipogenesis gene mRNA levels of SP and CP rats. However, the hepatocytes of SP rats were slightly hypertrophic. In addition, histological analysis revealed that the pancreases of SP rats had more islet areas than those of CP rats. This study demonstrated that feeding an SP-only diet for 12 days induces glucose intolerance, suggesting that the consumption of absorbable food, like a soft diet, may trigger glucose metabolism insufficiency and lead to life-threatening diseases.