Objective: The aim of this study was to evaluate the effects of rice as a carbohydrate source and its molecular mechanisms on insulin resistance induced by a high-fat diet (HFD).
Methods: C57 BL/6 J mice were divided into three groups and were fed a low-fat diet (LFD); a HFD (with 18% fat, 0.5% cholesterol, 51.5% w/w cornstarch and sucrose); or a HFD with rice (HFD-CR, with 18% fat, 0.5% cholesterol and 51.5% w/w rice powder) for 12 wk. In the HFD-CR diet, cooked rice powder was substituted for cornstarch and sucrose in the HFD as a carbohydrate source.
Results: HFD-CR–fed mice had significantly lower body weight, blood glucose, insulin and leptin levels and ameliorated glucose responses with decreased homeostasis model assessment-insulin resistance compared with HFD-fed mice. Hepatic mRNA levels of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase were down-regulated in the HFD-CR group. The hypertrophied islet size and the decreased pancreatic mRNA expression of glucose transporter 2 in the HFD group were normalized with cooked rice consumption. Rice promoted glucose uptake by activating AMP-activated protein kinase and downstream glucose transporter 4 in the skeletal muscle.
Conclusion: Rice consumption as a carbohydrate source might potentiate improvements in glucose uptake via AMP-activated protein kinase activation and glucose transporter 4 expression in the skeletal muscles, thereby improving insulin sensitivity.
Alex’s Notes: Asian diets and lifestyles are slowing becoming more Western, and an unsurprising consequence of this shift is an increase in metabolic disorders such as diabetes. One of the staple foods of a traditional Asian diet is white rice, which has been shown to be more beneficial for blood glucose and insulin than the Western bread counterpart. On a related note, epidemiological studies have reported that in individuals who ate rice two to three times a week, incidence of diabetes after a six year follow-up was 12%, and in those who ate rice no more than once a week, it was 20%. Why is this one starch – rice – so much different than the other starch – bread? Well, the current study aimed to find out.
The study divided mice into one of three dietary groups for 12 weeks.
“A low-fat diet (LFD), HFD, and HFD that incorporated cooked rice (HFD-CR). The HFD contained (in percent weight) 20% casein as protein, 18% fat supplemented with 0.5% cholesterol and 51.5% carbohydrate (21.5% cornstarch and 30% sucrose). The HFD-CR included 51.5% rice as a carbohydrate source by replacing 21.5% of the cornstarch and 30% of the sucrose.”
Note that the rice replaced corn and sugar – two staples of a typical Western diet. The results are fascinating, and I list the HFD-CR results below.
- 16% less weight gain compared to HFD despite identical food intake
- 43% less visceral fat gain compared to HFD
- No significant change from LFG for leptin, insulin, or adiponectin, while the HFD had a 4-fold increase in leptin, and nearly 2.5-fold increase in insulin
- 68% increase in fasting glucose compared to LFG, while the HFD had a 181% increase
- No significant change to HOMA-IR while the HFD increased by 685%
- Prevented the pancreatic islet cell hypertrophy seen in the HFD
- Up-regulated Glut-2 gene expression in the pancreas to levels similar in the LFD group
- Increase Glut-4 gene expression in the muscle tissue as well as the AMPK and AKT levels
So what does all this mean? In a nutshell, the high-fat Western diet lead to increased fat mass, glucose intolerance, insulin resistance, and pancreatic damage, but substituting rice for the corn and sugar attenuated many of the changes in weight and gene expression while completely preventing the increases in insulin sensitivity and pancreatic damage. These changes are through improved glucose uptake into tissues such as the muscle and improved functioning of the liver and pancreas. So if you have to choose between corn-on-the-cob and a soda, or some lovely polished white rice, go with the rice.