The effect of manipulating the macronutrient composition of meals on postprandial lipid metabolism

Dietary lipid intake is directly related to the levels of circulating lipids and lipoproteins, and is associated with the onset of obesity, cardiovascular disease and insulin resistance. Current evidence suggests that the magnitude and duration of postprandial lipaemia (PPL), and subsequent effects on substrate oxidation following a meal may be manipulated by altering the macronutrient composition of the meal, yet few studies have examined both circulating lipids and lipid oxidation in one study. The aims of the research were to examine the effect of manipulating the macronutrient composition of a meal on postprandial lipid metabolism paying particular attention to the control of lipid oxidation.Indirect calorimetry and plasma concentrations of lipids were used in conjunction with stable isotope tracer methodology to examine the postprandial metabolism of dietary lipid following a series of modified testmeals (lipid and carbohydrate content) containing a labelled triacylglycerol ([1,1,1-13C]tripalmitin) in a group of healthy, young subjects. Stool and breath specimens were collected and analysed for their 13C-enrichment, whilst plasma specimens were collected and analysed for lipid concentrations and 13C-enrichment.The magnitude of intra-individual variability in all measures was small compared to previous studies, and was used to conduct power analysis. The magnitude of PPL increased with the consumption of a high fat meal, and a low sucrose meal, with subsequent increases in lipid oxidation. In contrast, PPL decreased with the addition of 50g of sucrose, whilst the duration of PPL was extended with 100mg of sucrose. The addition of sucrose suppressed endogenous lipid oxidation, whilst exogenous lipid oxidation decreased only with 100g of sucrose. The mechanism relating PPL and substrate oxidation remains unclear, however, the results suggest that the rate of fatty acid oxidation may have a 'negative feedback' effect on circulating lipid concentrations resulting in raised PPL when lipid oxidation is suppressed. By manipulating the macronutrient composition of the meal, it is possible to alter the rate of lipid oxidation and therefore the circulating lipid response, which may in turn manipulate the relationship between dietary lipid and disease.