Abstract
The fatty acid, lauric acid (‘C12’), and the amino acid, tryptophan (‘Trp’), when given intraduodenally at loads that individually do not affect energy intake, have recently been shown to stimulate plasma cholecystokinin, suppress ghrelin and reduce energy intake much more markedly when combined. Both fatty acids and amino acids stimulate insulin secretion by distinct mechanisms; fatty acids enhance glucose-stimulated insulin secretion, while amino acids may have a direct effect on pancreatic β cells. Therefore, it is possible that, by combining these nutrients, their effects to lower blood glucose may be enhanced. We have investigated the potential for the combination of C12 and Trp to have additive effects to reduce blood glucose. To address this question, plasma concentrations of glucose, insulin and glucagon were measured in 16 healthy, lean males during duodenal infusions of saline (control), C12 (0.3 kcal/min), Trp (0.1 kcal/min), or C12+Trp (0.4 kcal/min), for 90 min. Both C12 and C12+Trp moderately reduced plasma glucose compared with control (p < 0.05). C12+Trp, but not C12 or Trp, stimulated insulin and increased the insulin-to-glucose ratio (p < 0.05). There was no effect on plasma glucagon. In conclusion, combined intraduodenal administration of C12 and Trp reduced fasting glucose in healthy men, and this decrease was driven primarily by C12. The effects of these nutrients on postprandial blood glucose and elevated fasting blood glucose in type 2 diabetes warrant evaluation.
Highlights
Fat or protein, when consumed immediately before a carbohydrate-containing meal, may reduce the postprandial glycaemic excursion in health and type 2 diabetes substantially [1,2,3]
There were no significant differences in baseline plasma glucose, insulin or glucagon between study days
C12 and C12 and Trp (C12+Trp), but not Trp, reduced the plasma glucose AUC compared with control, with no significant differences between C12+Trp and C12 or Trp
Summary
Fat or protein, when consumed immediately before a carbohydrate-containing meal, may reduce the postprandial glycaemic excursion in health and type 2 diabetes substantially [1,2,3]. There is considerable variation between nutrients in their effects to stimulate gut and glucoregulatory hormones; fat appears to be a more potent stimulant of GLP-1 than protein, whereas protein appears to have greater effects on insulin and glucagon [7,8]. Fatty acids enhance glucose-stimulated insulin secretion [9], while amino acids may have a direct effect on pancreatic β cells to simulate insulin release independent of glucose [10]. In this context, lauric acid, a fatty acid containing 12 carbon atoms (‘C12’), and tryptophan (‘Trp’), an aromatic amino acid, are of particular interest [11,12,13], since both potently stimulate pyloric
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