Improved Beta Cell Function, with Reduction in Secretion of Intact and 32/33 Split Proinsulin, after Dietary Intervention in Subjects with Type 2 Diabetes Mellitus

Diet in Type 2 diabetes often reduces both hyperglycaemia and weight and both these factors may contribute to improvement in beta cell function. Sixty‐nine subjects with newly diagnosed Type 2 diabetes had their glucose, insulin, intact and 32/33 split proinsulin measured at diagnosis, and after 16 (12–20) weeks of conventional diet. In the whole group following diet there was reduction in weight ( p < 0.0001), Haemoglobin A 1 ( p < 0.0001), and fasting glucose ( p < 0.0001). There was a fall in fasting intact proinsulin ( p < 0.03), 32/33 split proinsulin ( p < 0.0001), and the percentage of fasting proinsulin to total insulin‐like molecules ( p < 0.0001). Subjects were separated according to weight loss (group 1 < 0.5 kg, group 2 0.5–4 kg, group 3 > 4 kg). Only subjects in group 3 (mean weight loss 6.2 kg) had a fall in fasting insulin ( p < 0.04). The fasting glucose achieved following diet was positively correlated with the initial fasting glucose ( r = 0.7) and negatively correlated with the degree of insulin deficiency at diagnosis (with the initial 30 min insulin r = −0.62). The effect of diet on the final concentration of insulin, 32/33 split proinsulin and intact proinsulin was examined using multiple regression. The final insulin concentration was determined by the initial BMI and absolute weight loss, 32/33 split proinsulin concentration by the initial fasting glucose and absolute glucose fall, and intact proinsulin concentration by a combination of both weight loss and glucose reduction. We conclude that diet without weight loss increases the insulin secreted relative to the glucose concentration and reduces the concentration of proinsulin‐like molecules. Weight loss reduces insulin resistance thereby lowering the insulin and intact proinsulin concentrations.