A low glycaemic diet improves oral glucose tolerance but has no effect on β-cell function in C57BL/6J mice

Aim: Clinical studies have suggested a role for dietary glycaemic index (GI) in body weight regulation and diabetes risk. Here, we investigated the long‐term metabolic effects of low and high glycaemic diets using the C57BL/6J mouse model. Methods: Female C57BL/6J mice were fed low or high glycaemic starch in either low‐fat or medium‐fat diets for 22 weeks. Oral and intravenous glucose tolerance tests were performed to investigate the effect of the experimental diets on glucose tolerance and insulin resistance. Results: In this study, a high glycaemic diet resulted in impaired oral glucose tolerance compared to a low glycaemic diet. This effect was more pronounced in the group fed a medium‐fat diet, suggesting that a lower dietary fat content ameliorates the negative effect of a high glycaemic diet. No effect on body weight or body fat content was observed in either a low‐fat diet or a medium‐fat diet. Static incubation of isolated islets did not show any differences in basal (3.3 mM glucose) or glucose‐stimulated (8.6 and 16.7 mM glucose) insulin secretion between mice fed a low or high glycaemic diet. Conclusion: Together, our data suggest that the impaired glucose tolerance seen after a high glycaemic diet is not explained by altered β‐cell function.