We demonstrated that whey protein, when given before or with a high-carbohydrate meal, resulted in a substantial reduction in postprandial glycemia in diet-controlled type 2 diabetic patients. Given that the magnitude of the reduction was comparable with what would be hoped for using pharmacological therapy, such as sulfonylureas, these data have considerable implications for nutritional strategies in the management of diabetes.
The pivotal role of the gastrointestinal tract in determining postprandial glycemia has often been overlooked, but it is assuming increasing prominence, partly because of the development of gut peptide–based therapies for diabetes, such as the GLP-1 analog exenatide (8
) and the amylin analog pramlintide (9
), which may act predominantly by slowing gastric emptying. Similar to what we reported after an oil preload (4
), whey slowed gastric emptying substantially, in particular when given before the meal, and is associated with the stimulation of GLP-1 and CCK. However, in contrast to the delayed insulin response observed after oil, whey augmented insulin secretion markedly, possibly by a combination of the incretin effect and the direct stimulation of the β-cells by absorbed amino acids (10
). It is likely that the stimulation of insulin by whey was responsible for the much greater reduction in glycemia after whey than after oil, given that the effects on gastric emptying were comparable.
Although our study involved a small number of subjects who had well-controlled, predominantly uncomplicated type 2 diabetes, the improvement in postprandial glycemia was marked and highly consistent. Further evaluation is now required in poorly controlled patients and those taking oral hypoglycemic agents in order to determine whether the acute effects are sustained in the longer term. It would also be important to confirm whether the effects are evident with a smaller load of protein in order to minimize additional energy intake. Although concerns have been raised about hyperinsulinemia as a risk factor for vascular disease (11
), it is more likely that it represents a marker for other risk factors (12
), and in the UK Prospective Diabetes Study (UKPDS), stimulation of insulin by sulfonylureas was not associated with increased cardiovascular events (13
The concept of using dietary manipulations to treat type 2 diabetes, based on our knowledge of the contribution of gastric emptying and gut peptides to postprandial glycemic responses, appears to hold much promise.