Medium-chain Triglycerides Ingestion Research Articles

Metabolic and hormonal responses to lipid and carbohydrate diets during exercise in man

Nine healthy subjects were studied to determine their performance and the metabolic and hormonal responses to prolonged exercise after ingestion of a carbohydrate or a lipid diet. Subjects exercised on a bicycle ergometer (60% VO2max) until exhaustion four times at weekly intervals. The exercise test was performed 1 h after ingestion of three different isocaloric meals (400 Kcal) containing either glucose, medium-chain triglycerides (MCTs) or long-chain triglycerides (LCTs). The fourth test was performed after a night fast. The metabolism of these nutriments was followed using [U-13C]glucose, [1-13C]octanoate, and [1-13C]palmitate added as tracers. The average work time was comparable whatever nutriment used (116 +/- 11 min). Oxidation of the ingested nutriment over this period was 80% for glucose, 45% for MCTs, and 9% for LCTs. Glucose ingestion produced an early insulin peak associated at the end of the exercise with a lower glycemia compared to the fat diets. After MCT ingestion, an increase in ketone bodies was observed. Catecholamine response to physical exercise was decreased by all the meals when compared to fasting. Thus, we conclude that a different lipid meal, MCTs, or LCTs, compared to glucose feeding, do not modify exhaustion time in spite of differences in hormonal and metabolic responses.

Identification and quantification of octanoyl glucuronide in the urine of children who ingested medium-chain triglycerides.

In addition to the previously described metabolites, octanoyl glucuronide was identified in the urine of four children who received medium-chain triglycerides. Octanoyl glucuronide in the urine of a child after ingestion of medium-chain triglycerides (C8:C10, 3:1) was quantitated as octanoic acid after glucuronidase treatment by means of gas chromatography/mass spectrometry. The urinary excretion increased rapidly to a maximum 1-2 h after ingestion, and decreased thereafter. During 0-3 h, 6.11 mumol of octanoyl glucuronide was excreted, which comprised 0.034% octanoic acid administered as glyceride, and 0.07% octanoic acid was postulated to be excreted as glucuronide within 24 h. Neither decanoyl glucuronide nor hexanoyl glucuronide was detected. Glucuronidation of branched medium-chain fatty acids, whose beta-oxidation is hindered, has been described previously. The present findings show that even straight-chain fatty acids undergo glucuronidation, although to a lesser extent, in addition to omega-oxidation and beta-oxidation.

Thermic effect of medium-chain and long-chain triglycerides in man

The thermic effects of 400 kcal meals of medium-chain triglycerides (MCT) and long-chain triglycerides (LCT) were compared in seven healthy men. Metabolic rate was measured before the meals and for 6 h after the meals by indirect calorimetry. Mean postprandial oxygen consumption was 12% higher than basal oxygen consumption after the MCT meal but was only 4% higher than the basal oxygen consumption after the LCT meal. There was a 25-fold increase in plasma beta-hydroxybutyrate concentration and a slight increase in serum insulin concentrations after MCT ingestion but not after LCT ingestion. Plasma triglyceride concentrations increased 68% after the LCT meal and did not change after the MCT meal. These data raise the possibility that long-term substitution of MCT for LCT would produce weight loss if energy intake remained constant.

Effect of dietary medium chain triglyceride on lipogenic enzyme activity in rat liver.

This study was conducted to confirm that medium chain triglyceride (MCT) feeding itself would increase hepatic lipogenic enzyme activity without causing a lack of essential fatty acids (EFA) in the liver. Male weaning rats were fed for 11 weeks on diets containing 2% corn oil and 13% various fats: MCT, corn oil, tripalmitin or beef tallow, respectively. MCT feeding was clearly shown to increase the activities of fatty acid synthetase (FAS) and malic enzyme (ME) in the liver. Rats weighing 170 g were pair-fed for 7 days on diets containing 15% MCT, 13% MCT + 2% corn oil, 15% corn oil, and 2% corn oil and no fat (control groups), respectively, under a fixed level of carbohydrate (sucrose). The addition of 2% corn oil to MCT (13%) did not depress these enzyme activities, even though supplementing the fat-free diet with 2% corn oil resulted in a significant decline in the activities. When the rats received various amounts of MCT, the extent to which the degree of FAS and ME activities increased by MCT feeding depended on the amount of MCT in the dietary fat mixture with corn oil. Supplement of over 5% corn oil to MCT diets did not inhibit them sufficiently. In the liver lipids of animals fed MCT, there were no appearances of 20:3 omega 9 (5,8,11-eicosatrienoic acid), but the levels of mono-unsaturated fatty acids were increased by MCT feeding. The results suggest that MCT ingestion itself enhances lipogenic enzyme activity via some metabolic charge.

Effect of equimolar amounts of long-chain triglycerides and medium-chain triglycerides on plasma cholecystokinin and gallbladder contraction

The present study was undertaken to compare the effects of equimolar amounts of long-chain triglycerides (LCT) and medium-chain triglycerides (MCT) on plasma cholecystokinin (CCK) concentrations and gallbladder contraction in man. On separate mornings and in random order six healthy volunteers ingested either 60 mmol LCT or 60 mmol MCT. Plasma CCK concentrations were measured by a sensitive and specific radioimmunoassay and gallbladder contraction by ultrasonography. Ingestion of LCT induced significant increases in plasma CCK from 2.8 ± 0.5 to 6.5 ± 0.7 pmol/1 (p < 0.005) and decreases in gallbladder volume from 33.4 ± 5.9 to 13.2 ± 4.2 cm3 (p < 0.005). On the other hand, no significant changes in plasma CCK and gallbladder volume were found after MCT. Ingestion of MCT was followed by abdominal cramps and diarrhea, while LCT were without side effects. It is concluded that, in contrast to LCT, MCT do not induce CCK release and gallbladder contraction.

Ketogenic Response to Medium-Chain Triglyceride Load in the Rat

We studied ketonemia induced in rats by a single oral load of medium-chain triglycerides (MCT) (C8:0 50.5%, C10:0 48.0%, C12:0 1.0%). Medium-chain fatty acids, rather than being incorporated into the lipids synthesized by the liver, are oxidized there, with high production of ketone bodies. Severe and long-lasting hyperketonemia developed rapidly. With increased MCT loads, ketonemia also increased, although not linearly. The level of the hyperketonemia seemed equal in the two sexes. Ingestion of MCT by fasting rats caused an additional rise in ketonemia. Long-chain triglycerides were not ketogenic, since their constituent fatty acids are incorporated into lipids and are thus less subject to oxidation. Lipids induce less severe ketonemia in genetically obese rats than in normal-weight rats.

A disorder of muscle lipid metabolism and myoglobinuria. Absence of carnitine palmityl transferase.

Two brothers, 29 and 33 years of age, had recurrent myoglobinuria, renal failure and azotemia, but were otherwise normal, without apparent muscle weakness or exercise intolerance. Ischemic exercise resulted in normal lactate production. Muscle glycogen content and activities of phosphorylase and phosphofructokinase were normal. Plasma triglycerides were elevated (500 mg per deciliter) on a regular diet and rose during fasting. During a 72-hour fast, serum creatine phosphokinase rose more than 10 times, and myoglobin was detected in urine. Plasma ketone production was minimal during fasting, but prompt ketonemia ( a normal response) occurred after ingestion of medium-chain triglycerides. Carnitine palmityl transferase activity was virtually absent in crude muscle extracts and mitochondrial fractions. Lack of this enzyme impairs long-chain fatty acid utilization, reflected in increased content of plasma free fatty acids and plasma triglycerides. Depletion of ATP because of this metabolic block in muscle may account for the attacks of myoglobinuria.

Standardized ketosis in man following medium chain triglyceride ingestion

Ingestion of medium chain triglycerides (MCT) results in a quantitatively reproducible increase of acetone concentrations in end-expiratory air as measured by gas chromatography. Acetone concentrations rise rapidly, reach a maximum several hours after ingestion of MCT and gradually return to base-line values. Under standardized conditions, ingestion of increasing amounts of MCT results in increasing acetone concentrations. Repeated tests in the same subject are reproducible within narrow limits. The acetone response is quantitatively suppressed by the administration of increasing amounts of sucrose. Maximal acetone concentrations increase with prolongation of fasting before ingestion of MCT. Three insulin-dependent diabetics had an acetone response in the MCT test 2 1 2 times greater than the mean response of 4 normal subjects. The acetone response of a thiazide-induced diabetic was normal. Interpretation of the results of MCT tests in normal subjects is that the magnitude of ketosis in man is the result of carbohydrate deficiency relative to the amount of fat entering the liver. The MCT test is a means of measuring the tendency of a subject to develop ketosis in response to a standardized fat load and may be useful for the classification of diabetes mellitus.