Triglyceride clearance during diets rich in carbohydrate or fats

Development of hypertriglyceridemia in patients with enterocutaneous fistulas

BACKGROUND & AIMS

Hypertriglyceridemia is commonly observed in patients with enterocutaneous fistulas, compromising their health status. In this study potential causes for hypertriglyceridemia in patients with an enterocutaneous fistula are explored and treatment options discussed accordingly.

METHODS

A database was created consisting of all consecutively treated patients with an enterocutaneous fistula from 1991 until 2007. Two successive measures of serum triglyceride concentrations of more than 3.0 mmol/L (266 mg/dL) were regarded as hypertriglyceridemia. The relation between fistula specific characteristics and hypertriglyceridemia was analyzed using a multivariable Cox proportional hazard model with time-dependent covariates.

RESULTS

A total 102 patients were eligible for this study of whom 25 had hypertriglyceridemia. Multivariable analysis showed that sepsis (HR 4.503, CI 1.778-11.401, P=0.002), high output small bowel fistula (HR 3.534, CI 1.260-9.916, P=0.016), parenteral nutrition (HR 5.689, CI 1.234-26.216, P=0.026) and inflammatory diseases (inflammatory bowel disease vs. malignancy HR 6.211, CI 1.081-35.696, P=0.041) were independent predictors of hypertriglyceridemia.

CONCLUSIONS

High triglyceride concentrations in patients with an enterocutaneous fistula were mainly associated with sepsis, a high output small bowel fistula, nutrition by the parenteral route and primary diseases with inflammatory aetiology. This should direct a treatment strategy that focuses on these aspects.

Dietary fatty acids, lipoproteins, and cardiovascular disease

Dietary fat quality and quantity significantly affect the metabolism of all the plasma lipoproteins and probably constitute the most significant dietary determinants of plasma lipoprotein levels. Since the major role of the plasma lipoproteins is the transport of exogenous and endogenous fat, this would be expected of a highly regulated, metabolically homeostatic system. The data clearly show that dietary fat saturation affects all aspects of lipoprotein metabolism, from synthesis to intravascular remodeling and exchanges to receptor-mediated and nonspecific catabolism. The experimental data regarding dietary fatty acid effects on lipoprotein metabolism are complicated and at times contradictory due to the large degree of metabolic heterogeneity in the population, which, when coupled with the known abnormalities of lipoprotein metabolism associated with certain types of hyperlipoproteinemia, can present responses from A to Z. It is clear that the same dietary pattern has different effects in different individuals and that complicating factors of individuality raise some concerns regarding generalized dietary recommendations. As new knowledge of the role of dietary factors and CVD risk develops, and our abilities to characterize the individual patient's response to dietary interventions become more refined, it may be possible to specify dietary fat intervention from a patient-oriented concept rather than a single all-purpose diet approach. Thus it would be possible to design dietary interventions to match patient needs and gain both efficacy and compliance. With the spectrum of approaches possible--low fat, moderate fat with MUFA, n-3 PUFA, etc.--we should be able to approach dietary interventions to reduce CVD risk at both a population-based level and a patient-specific level. There remains much to learn regarding the effects of dietary fatty acids on the synthesis, intravascular modifications, and eventual catabolism of the plasma lipoproteins. The area of lipoprotein metabolism in health and disease, of its modifications by diets and drugs, and of the contributions of genetic heterogeneity to these processes is one of notable advances over the past two decades and continues to be an area of intense investigation.

Suppression by diets rich in fish oil of very low density lipoprotein production in man

The highly polyunsaturated fatty acids in fish oils lower the plasma triglyceride concentration. We have studied the effect of a diet rich in fish oil on the rate of production of the triglyceride-transporting very low density lipoprotein (VLDL). Seven subjects, five normal and two with hypertriglyceridemia received up to 30% of daily energy needs from a fish oil preparation that was rich in eicosapentaenoic acid and docosahexaenoic acid, omega-3 fatty acids with five and six double bonds, respectively. Compared with a diet similarly enriched with safflower oil (in which the predominant fatty acid is the omega-6 linoleic acid, with two double bonds), the fish oil diet lowered VLDL lipids and B apoprotein concentrations profoundly. High density lipoprotein lipids and A1 apoprotein were also lowered, but the effect on low density lipoprotein (LDL) concentration was inconsistent. The daily production or flux of VLDL apoprotein B, calculated from reinjected autologous 125I-labeled lipoprotein, was substantially less in six subjects studied after 3 wk of fish oil, compared with after safflower oil. This effect on flux was more consistent than that on the irreversible fractional removal rate, which was increased in the four normolipidemic but inconsistent in the hypertriglyceridemic subjects. This suggests that fish oil reduced primarily the production of VLDL. The daily production of VLDL triglyceride, calculated from the kinetics of the triglyceride specific radioactivity-time curves after [3H]glycerol was injected, also showed very substantial reductions in five subjects studied. The marked suppression in VLDL apoprotein B and VLDL triglyceride formation was found not to be due to diminished plasma total free fatty acid or plasma eicosapentaenoic flux, calculated during constant infusions of [14C]eicosapentaenoic acid and [3H]oleic acid in four subjects. In two subjects there was presumptive evidence for substantial independent influx of LDL during the fish oil diet, based on the precursor-product relationship between the intermediate density lipoprotein and LDL apoprotein B specific radioactivity-time curves.

Metabolic utilization of intravenous fat emulsion during total parenteral nutrition

The effect of nutritional therapy on the utilization of an intravenous fat emulsion was studied in patients with injury, infection, and nutritional depletion using I-14C-trioleate labeled Intralipid. The plasma fractional removal rate and 14C-Intralipid oxidation rate was 55% ad 25% higher, respectively, in patients following trauma and during periods of infection receiving 5% dextrose than in healthy control subjects. Total parenteral nutrition (TPN) was administered as either 1) nonprotein calories given as glucose (Glucose System) or 2) equal proportions of glucose and intravenous fat emulsion (Lipid System). In comparison to TPN with the Lipid System, administration using the Glucose System resulted in higher plasma clearance rates and lower oxidation rates in both acutely ill and depleted patients. There was no correlation between the rates of plasma removal and oxidation of the intravenous fat emulsion (r = -0.04; NS) indicating that the removal of exogenous fat from plasma cannot be used as an indicator of oxidation. A negative linear relationship was seen between the oxidation rate of intravenous fat and carbohydrate intake (r = -0.92; p less than 0.001). Glucose intakes exceeding energy expenditure did not totally inhibit oxidation of the fat emulsion. The oxidation rate of 14C-Intralipid was linearly related to net whole body fat oxidation calculated using indirect calorimetry (r = -0.90; p less than 0.001) suggesting that the fat emulsion was oxidized in a similar manner to endogenous lipids. This study suggests that intravenous fat emulsions are utilized as an energy substrate in patients with major injury, infection or nutritional depletion. This observation, along with a relative unresponsiveness to glucose in surgical patients suggests that fat emulsions may be useful as a calorie source in patients receiving parenteral nutrition.

Acute dietary effects on plasma lipids, lipoproteins and lipolytic enzymes in healthy normal males

Diurnal plasma lipids and lipoproteins were studied in twelve healthy young males on corn oil and palm oil diets, respectively. The major triglyceridy. Lecithin-cholesterol acyl transferase, lipoprotein lipase and hepatic triglyceride lipase were also measured. diurnal changes of triglycerides and cholesterol were confined to lipoproteins of d less than 1.006 kg/l. There was a diurnal rise of lecithin-cholesterol acyl transferase activity with corn oil but not with palm oil. Fasting and postprandial postheparin lipoprotein lipase and hepatic triglyceride lipase were similar but there was a significant correlation of postprandial hepatic lipase with postprandial plasma triglycerides on palm oil. Marked diurnal changes of triglyceride fatty acids were observed not only in 'very low density lipoprotein' but also in high-density lipoprotein amounting to approximately one third of total high density lipoprotein triglyceride fatty acids.

Sucrose-induced changes in VLDL- and LDL-B apoprotein removal rates

Dietary sucrose has been shown to increase triglyceride transport in very-low-density lipoproteins (VLDL), but it is not known whether the metabolism of the entire particle is affected. Measurements were therefore carried out on VLDL-B apoprotein flux and removal rate before and after the consumption of high sucrose diets (55% of calories). Autologous 125I-labeled VLDL were injected and the specific activity-time curves analyzed by two-pool kinetics. Two kinds of response to sucrose were seen. In two subjects, the pool of VLDL-B apoprotein decreased by 20% and 14% (despite increased fluxes) due to substantial increases in removal rates of 42% and 116%. In four subjects, pool size expanded by 154%, 426%, 50% and 105%, primarily as the result of decreased removal rates (decreases of 55%, 67%, 30%, and 43%). Changes in flux were inconstant, suggesting that accumulation of VLDL particles was related to delayed clearance rather than to increased formation. This may reflect the longer time required to remove the larger load of triglyceride from each particle. The catabolic rate of low-density lipoprotein (LDL) was also measured in five subjects: in four, the clearance of LDL increased with sucrose and was associated with decreases in LDL-B apoprotein and plasma cholesterol.

Changes in lactate dehydrogenase, LDH isoenzymes, lactate, and pyruvate as a result of feeding low fat diets to healthy men and women

A study was conducted to evaluate the effects on blood lipids and lipoproteins of feeding 21 healthy volunteers, 40-60 yr old, foods commonly eaten in the United States for two 40-day periods. Activities of lactate dehydrogenase (LDH) and LDH isoenzymes, lactate, and pyruvate were monitored. Results showed that LDH activity was significantly lower in all subjects at the end of the 25% fat-calorie period (period I) than at the beginning of the study, but rose above initial levels at the end of the 35% fat-calorie period (period II). While total LDH fell during period I, relative activity of M type subunits of LDH rose significantly in relation to H type in both sexes. This rise is probably indicative of an increase in glycolytic activity as a consequence of the increased intake of dietary carbohydrate. In period I, lactate and pyruvate decreased significantly in males (pyruvate greater than lactate) but not in females. Values for males returned to near initial levels in period II. The ratio of lactate/pyruvate was elevated in both sexes after period I. The greater change in pyruvate relative to lactate with increased dietary carbohydrate suggests increased Krebs Cycle activity. There was a statistically significant positive correlation between lactate, pyruvate, and serum triglyceride for males after they ate the 25% and 35% fat-calorie diets and for females after they ate the 35% fat-calorie diet, but not between lactate, pyruvate, and serum cholesterol for either sex.

Differences among hyperlipoproteinaemic subjects in the response of lipoprotein lipids to resin therapy

Ih has been reported that cholesterol turnover is raised when hypercholesterolaemia occurs in association with elevated levels of very low density lipoprotein, but normal when hypercholesterolaemia reflects an increase in the concentration of low density lipoprotein alone. The relationship of plasma lipoprotein levels to cholesterol metabolism has been further investigated in the present experiments, in which the acute effects on lipoprotein lipids of stimulating cholesterol turnover with a bile acid-sequestering resin, colestipol, have been compared in normal subjects and in patientw with four types of hyperlipoproteinaemia. Very low density lipoprotein (VLDL) lipids increased in every subject. The increase was greatest in patients with type IV or type V hyperlipoproteinaemia, least in normal subjects and in those with type IIa hyperlipoproteinaemia, and intermediate in patients with type IIb hyperlipoproteinaemia. The induced increments in VLDL cholesterol and triglyceride mass were accordingly positively correlated with the pre-treatment concentrations. Low density lipoprotein (LDL) lipids decreased during resin therapy in all subjects, except those with type IV or type V hyperlipoproteinaemia in whom there was a transient rise. The reductions in LDL cholesterol were significantly greater in patients with type II hyperlipoproteinaemia than in the normal volunteers, and in both groups of subjects were proportionately greater than those in LDL triglyceride. These findings demonstrated clear differences among the hyperlipoproteinaemias in the response of lipoprotein lipids to resin therapy, and profide further evidence for the heterogeneity of cholesterol metabolism in these conditions. The colestipol-induced changes in type UV and type V patients could be partially reproduced in normal subjects during the consumption of high carbohydrate diets, which might be expected to increase VLDL synthesis. It is suggested, therefore, that the synthesis of VLDL cholesterol may be enhanced in such patients, and that any rise in LDL cholesterol observed during resin therapy reflected subsequent metabolism of VLDL to LDL rather than diminished LDL cholesterol clearance.