Triglycerides can be present in the plasma from dietary sources packaged in chylomicrons or from endogenously produced fatty acids packaged into very low density lipoproteins (VLDL). Plasma VLDL-triglyceride levels are often measured along with other lipoproteins to form lipid profiles that can indicate metabolic abnormalities. Raised plasma triglycerides are a risk factor for cardiovascular disease because postprandial hypertriacylglycerolaemia is associated with atherosclerosis. High carbohydrate intakes are associated with elevated plasma triglyceride levels, despite recommendations for those at risk of cardiovascular disease to consume high carbohydrate low fat diets. Excess carbohydrate not used to synthesise glycogen or for immediate energy needs is converted to fatty acids in the liver in a process called de novo lipogenesis. These fatty acids are then incorporated into VLDL and exported to peripheral tissues such as muscle and adipocytes.
Most of the research on triglyceride levels has been performed in metabolic units and involved feeding subjects macronutrients to assess their impact on plasma triglyceride levels. Results from these studies have shown step wise increases in plasma triglyceride levels after consumption increasing levels of fat in the diet. From these results it has been interpreted that dietary fat is able to raise plasma triglyceride levels. However, these feeding studies do not reflect the normal consumption of mixed meals in the general population. To address these problems, researchers1 allowed subject to self test their own triglyceride levels at home at 6 time points over a 3 day period. From the daytime triglyceride levels, profiles of triglycerides were calculated for absolute and incremental changes. Food intake was recorded in a food diary in order to calculate associations.
The results showed that mean energy intake was 2599 kcal/d (33% fat, 48% carbohydrate and 16% protein), and the mean fasting triglyceride concentration was 1.20 mmol/L. Analysis of the data showed that the plasma triglyceride levels were not related to dietary intakes of triglycerides. The change in triglycerides (as area under the curve) was significantly related to carbohydrate intake (r = 0.38), protein intake (r = 0.29) as well as total energy (r = 0.28), but negatively associated with fat intake (r = -0.30). As dietary fat intake increased amongst the subject, dietary carbohydrate levels went down. Changes in plasma triglyceride levels were significantly lower in those with the highest intake of fat compared to those with the lowest intake of fat, suggesting that the changes in triglyceride levels were associated with the carbohydrate content of the diet in free-living individuals.
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