Increased insulin binding to adipocytes and monocytes and increased insulin sensitivity of glucose transport and metabolism in adipocytes from non-insulin-dependent diabetics after a low-fat/high-starch/high-fiber diet

Nine non-insulin-dependent diabetics were studied before and after 3 weeks on an isoenergetic high-fiber/high-starch/low-fat diet (alternative diet), and nine non-insulin-dependent diabetics were studied on their usual diet. In the group that ate the alternative diet, the intake of fiber and starch increased 120% and 53%, whereas fat intake decreased 31%. Diabetes control improved as demonstrated by decreased fasting plasma glucose (P < 0.05) and 24-hour urinary glucose excretion (P < 0.05). The in vivo insulin action increased (K_IVITT increased, P < 0.05) with no change in fasting serum insulin levels. In fat cells obtained from patients in the alternative-diet group, insulin receptor binding increased (P < 0.05) after the change of diet. Insulin binding to purified monocytes (more than 95% monocytes) also increased (P < 0.05), whereas no change was found in insulin binding to erythrocytes. When lipogenesis was studied at a tracer glucose concentration at which glucose transport seems to be rate limiting, insulin sensitivity increased (P < 0.02). This is the predicted consequence of increased receptor binding. Moreover, when CO₂ production and lipogenesis were studied at a higher glucose concentration, where steps beyond transport seem to be rate limiting for glucose metabolism, increased insulin sensitivity was also observed. In contrast, no change was found in maximal insulin responsiveness. Fat and blood cells from the patients who continued on their usual diet showed no changes of the mentioned quantities. In the total group of non-insulin-dependent diabetics, fat cell insulin binding as well as rates (both basal and maximal insulin-stimulated rates) of glucose transport, CO₂ production, and lipogenesis were very heterogeneous, but when results from the first and second fat biopsy from the same patient were compared, these values varied only slightly. We conclude that the beneficial effect of a high-fiber/high-starch/low-fat diet on metabolic control in diabetics may in part be mediated through an increased insulin-binding ability of target cells for insulin, which causes an increased insulin sensitivity in these cells.