Zeitschrift fur Ernahrungswissenschaft最新文献

Hypersecretion of biliary cholesterol appears to be the key defect in the pathogenesis of cholesterol gallstones, and this may be due to an enhanced synthesis of cholesterol. To measure fractional syntheses of biliary and plasma cholesterol, five male and 3 female healthy humans with an intact enterohepatic circulation were infused intravenously with [1-13C]acetate for 15 h. Samples of duodenal bile and blood were taken hourly and an enteral formula diet was given. Free cholesterol mass distribution was analyzed by gas chromatography mass spectrometry. The Mass Isotopomer Distribution Analysis (MIDA) technique allowed to calculate fractional synthesis. After 6 hours of infusion, the [13C]label of the cytosolic acetate pool reached a plateau of approximately 12%. Individual fractional cholesterol synthesis is plasma and bile correlated significantly (6-15 h) and amounted to 4.2% and 5.3% after 15 h, respectively. It may be concluded from this study, that newly synthesized cholesterol is secreted into bile to a higher extent than into plasma.

The disaccharide lactose is present as a natural component of foods only in milk and dairy products. In the gastrointestinal tract, lactose is hydrolysed by the enzyme beta-galactosidase (lactase) into glucose and galactose. These components are absorbed. With the exception of the caucasian race, the lactase activity decreases in most people at an age of 4 to 6 years. Lactose intake can cause symptoms of bloating, flatulence, abdominal pain, and diarrhea due to the lactose reaching the large intestine. This phenomenon is called lactose intolerance. It is generally recommended to those persons that they refrain from the consumption of milk and dairy products. However, most lactose intolerant people are able to digest small amounts of milk. They can also consume cheese that contains no (hard and semi-hard) or only small amounts of lactose (present in only 10% of soft cheeses). These products are very important sources of calcium. Compared to milk, the lactose content of yogurt is usually lower by about one third. Studies during the last 10 years have shown that in spite of its lactose content yogurt is very well tolerated by lactose intolerant persons. This advantage is ascribed to the presence of living lactic acid bacteria in fermented dairy products which survive passage through the stomach and also to the lactase present in these products.

The doubly labeled water method for the measurement of average daily metabolic rate (ADMR), combined with a measurement of resting metabolic rate, permits the calculation of energy expenditure for physical activity under normal daily living conditions. This procedure was used to evaluate the use of movement registration for physical activity assessment under daily living conditions. Subjects were 16 men and 14 women with normal weight (body mass index (BMI) 24.6 +/- 2.4 kg/m2). Their body movement was registered with a triaxial accelerometer over a 7-day interval, simultaneous with an ADMR measurement with a doubly labeled water method. Resting metabolic rate was measured overnight in a respiration chamber (sleeping metabolic rate (SMR)) at the start of the ADMR measurement. Subjects did wear the accelerometer during waking hours. Accelerometer output (AO, counts/min) was related to physical activity as quantified by adjustment of ADMR for SMR. Additional studies were performed in 11 subjects with anorexia nervosa (BMI 16.7 +/- 1.7 kg/m2) and 8 subjects with morbid obesity (BMI 45.3 +/- 6.8 kg/m2). AO explained most of the variation in ADMR, after adjustment for SMR (R2 = 0.64, SEE = 0.9 MJ/d) Average AO was 1108 +/- 293, 1144 +/- 318, and 946 +/- 391 for subjects with normal weight, anorexia nervosa, and morbid obesity, respectively, and was not significantly different between the three groups. However, in the anorectics AO was significantly related to body mass index (r = 0.84, (p < 0.01), subjects with a BMI17 kg/m2 were equally or more active compared with control subjects, while subjects with a BMI < 17 kg/m2 were equally or less active compared with control subjects. In the morbid obese group, 5 of the 8 subjects had a low activity level (AO < 900 counts/day) and the other 3 had a high activity level (AO1150 counts/day). The triaxial accelerometer is an objective method that can be used to quantify physical activity related energy expenditure and to distinguish differences in activity levels between individuals.

To investigate the alpha 2-adrenergic effect on the metabolic rate, young bulls were exposed to environmental variants (feeding levels of 1.0 and 1.6 times the MEm and ambient temperatures of 18 degrees C and 4 degrees C) and treated preprandially with a alpha 2-adrenergic agonist (clonidine) in each case. The heat production (HP) was continuously measured by indirect calorimetry using climatized respiratory chambers. Post-clonidine, the preprandial HP fell in all variants but the strongest decrease occurred at 4 degrees C, 1.6 times the MEm. The postprandial HP rose 1.3-fold the HP of animals received the carrier (saline) at 4 degrees C, 1.6 times the MEm. Animals exposed to 18 degrees C, 1.6-fold the MEm did not significantly increase the postprandial HP after clonidine administration, suggesting different sympathetic outflow corresponded to differing resting metabolic rate, occurring in the environmental variants. Circulating fuels (glucose, non-esterified fatty acids) responded to alpha 2-adrenergic reduction of the sympathetic outflow but did not parallel the HP changes. Studies on monocytes revealed a linear correlation (r2 > 0.9) between resting metabolic rate and expression of sulfonylurea receptors, the constitutive component of ATP-sensitive K+ channels (KATP) suggesting a function of KATP in coupling the systemic HP with cellular metabolism.

Intervention studies have shown that the adaptation of fat oxidation to fat intake, when changing the dietary fat content, is not abrupt. This study was conducted to measure the time course of adaptation of oxidation rates to increases in the fat content of the diet, when feeding subjects at energy balance. Twelve healthy, non-obese males and females (age: 26 +/- 2, BMI: 21.4 +/- 0.5, habitual fat intake: 29 +/- 1% energy) consumed a low-fat diet for 6 days (days 1-6) followed by a high-fat diet for 7 days (day 7-13). Days 5-9 and day 13 were spent in a respiration chamber. After adjusting energy intake to 24h energy expenditure on day 5, subjects were in energy balance (range -0.15 to +0.23 kJ/day) on days 6-9 and day 13. Fat balance was zero on day 6 but became positive after changing to the high-fat diet (1.06 +/- 0.15, 0.75 +/- 0.15, and 0.55 +/- 0.14 MJ/day for days 7, 8, and 9 respectively, p. < 0.05), reaching a new balance on day 13, 7 days afterwards. Thus, in case of energy balance, lean subjects are capable of adjusting fat oxidation to fat intake within 7 days, when dietary fat content is increased.

Lean tissue growth occurs when the rate of protein synthesis exceeds the rate of protein breakdown. Although absolute rates of protein synthesis and breakdown rise during growth from birth to maturity fractional rates fall. Both these processes are sensitive to nutrient intake but responses to feeding vary greatly amongst different tissues. Protein, carbohydrate and fat can all stimulate body protein accretion in immature animals and in children but the mechanisms by which they do so, and the energy expenditures involved, seem to be different.

Actual amounts of free amino acids in the blood are sufficient to support whole body protein synthesis for some minutes only. This indicates that the levels of free amino acids in the circulation are kept small and constant relative to the amounts of amino acids supplied by daily intake and turnover of body proteins. The clearance of the amino acids originating from either endogenous or exogenous sources is mainly due to protein synthesis and metabolic degradation. The partitioning of dietary amino acids between these processes, on the short term, is supposed to play an important role in whole body amino acid economy. Therefore whole body amino acid economy could be improved by nutritional measures that favour the clearance of dietary amino acids by protein synthesis instead of by metabolic degradation. These nutritional measures should to be focused on threshold values for metabolic degradation of individual amino acids.

This presentation gives an overview about the factors involved in the regulation of gluconeogenesis. Then, based on these regulatory principles, the changes seen in impaired liver function are discussed. Gluconeogenesis from lactate and pyruvate is mediated through pyruvate carboxylase (PC) and phosphoenolpyruvate carboxykinase (PEPCK) activity. The PC mediated pathway depends on substrate supply and on the downregulation of the oxidative pathway for pyruvate. Both enzymes need ATP or GTP and, thus, depend on the cellular energy charge. Tissue anoxia can reduce the energy charge and limit the flow through the PEPCK pathway. Thus, one expects a coupling between reduced splanchnic blood flow, limited oxygen supply to the liver, resulting tissue anoxia, and reduced gluconeogenesis. Conditions are shown, where this coupling exists. Since gluconeogenesis is concentrated in the periportal region of the liver, the local oxygen tension is sufficient under many circumstances to maintain a high glucose production level. Also, the enzyme activity of PEPCK can compensate for long term anoxia. Thus, gluconeogenesis is sufficient in most cases, as seen in critically ill patients. However, this could be associated with a reduction in the perivenous oxygen tension, possibly below critical levels. Beta-adrenergic stimulation increases gluconeogenesis. Examples are shown where this stimulation can overlay the dependency on the oxygen tension and substrate supply. Catecholamines are generally used to stabilize the hemodynamic system. This treatment could limit splanchnic bloodflow and, as a consequence, the oxygen supply to the liver with a simultaneous stimulation of gluconeogenesis and can cause severe anoxia in the perivenous region. These negative side effects of catecholamine treatment should be avoided and the ideal treatment should aim at improving splanchnic flow without stimulation of gluconeogenesis.