Nutrition and metabolism最新文献

The average western diet contains approximately 40% of total calories as dietary fat or approximately 100 g of fat. The efficiency of the entire process of fat absorption can be judged by the fact that under normal conditions less than 5% of ingested fat is recovered in the stool. In the past several years, new concepts have greatly added to our understanding of the process by which dietary fat is digested, absorbed and processed in the intestinal epithelial cell for delivery to the body via the intestinal lymph and the portal venous system. These newer concepts include an understanding of the physical chemistry of lipids, the physiology of bile salts and the formation and metabolisms of lipoprotein all directly influencing the process of fat absorption. The present discussion will emphasize the formation of lipoproteins within the intestinal mucosa. New information suggests that the small intestinal mucosa is a quantitatively important source of lipoprotein constituents for systemic lipoproteins. This is hardly surprising when one considers the large quantities of lipid transversing the intestinal mucosa each day which must exit in the form of lipoproteins.

In sterilized spinach which was inoculated with bacteria, a reduction of NO3- to NO2-, due to their metabolic activity, was detectable, depending on the holding conditions. The reaction rate was highest in the presence of thermophilic bacteria. A lower reaction rate was altogether found with mesophilic bacteria which, depending on counts and holding time, may temporarily cause high nitrite contents. The reaction rate was lowest with cold-tolerant bacteria.

The intravenous application of the branched chain amino acid L-valine to patients with hepatic coma resulted in a specific drop of tryptophan, serotonin and 5-hydroxyindole acetic acid. Clinical improvement of hepatic encephalopathy and of the underlying neurotransmitter (serotonin) and ammonia derangements by administration of L-valine suggest a possible role of this competitive amino acid on intermediary metabolism and ammonia detoxification.

The rate-limiting step in adrenal steroidogenesis is associated with the mitochondrial-cytochrome-P450scc-dependent production of pregnenolone from cholesterol. This sterol side-chain cleavage reaction is influenced by the supply of cholesterol to the mitochondria. Cholesterol is stored as cholesterol esters while the cytosol contains a hormone-sensitive cholesterol ester hydrolase. This enzyme is activated by phosphorylation involving a cyclic AMP-dependent protein kinase and ATP; this enzyme preferentially attacks cholesterol oleate or cholesterol linoleate. The lipid composition of the adrenal cortex is influenced by diet so that animals on a low-fat diet tend to store cholesterol oleate and as the linoleate content of the diet is increased, the cholesterol linoleate content of the adrenal cortex increases. Animals maintained on a high erucate diet tend to store large amounts of cholesterol erucate in the adrenal cortex; such animals have an impaired adrenal cortical function. Animals maintained on a low-fat diet (marginally deficient in essential fatty acids), a linoleate-replete diet or a moderate erucate diet, all exhibited normal responses to ACTH and normal corticosterone production rates.

The rate of hydrolysis of the synthetic trypsin substrate N alpha-benzoyl-L-arginine-p-nitroanilide was determined from turnover rate curves, when the trace elements zinc, iron, cobalt, and nickel were added in the concentration range from 0.9 . 10(-7) to 0.9 . 10(-3) mol Men+/l. The enzyme substrate ratio was 1:50. An influence on the activity of trypsin, depending on the element used and on its concentration could be determined. Cobalt and iron accelerated the enzyme's capacity of hydrolysis at all concentrations used, whereas addition of higher but not toxic amounts of zinc or nickel resulted in an inhibition.

In the male rat a diet rich in beef fat facilitates the occurrence of hyperinsulinemia after a glucose load whereas fats rich in linoleic acid produce no such effect. The combination of saturated fat and saccharose facilitates the occurrence of hypertriglyceridemia in the male rat, no such effect is produced by the combination of fats rich in linoleic acid and saccharose. Linoleic acid prevents natrium chloride from provoking hypertriglyceridemia in male and in female rats subjected to a diet enriched in saccharose and fat. Estrogen-induced hypertriglyceridemia in castrated animals is strongly inhibited if the diet is rich in linoleic acid. Physical effort can prevent saccharose combined with saturated fats from inducing hypertriglyceridemia.

The polyene fatty acid composition of cardiac phospholipids is modified by age, diet and stress in the rat. In the aging heart there is a progressive replacement of 18:2n6 by 20:4n6 in phosphatidylcholine (PC) and a replacement of 18:2n6 by 22:6n3 in phosphatidylethanolamine (PE). Norepinephrine stress accelerates aging of cardiac PC and PE. Dietary fish oil causes a replacement of 18:2n6 and 20:4n6 by 22:6n3 in cardiac PC and PE but not in cardiolipin. Studies on human cardiac autopsy samples suggest that: (a) polyene fatty acid composition changes with age; (b) stability of cardiac phospholipids is a function of the fatty acid composition, chain length and unsaturation; (c) coronary atherosclerosis is associated with a reduced content of 18:2n6 in phospholipids, an increased content of glycerides of abnormal composition and an unexpectedly low level of free fatty acids (FFA) in the heart muscle, and (d) many cases of sudden cardiac death in the absence of marked coronary artery stenosis or myocardial infarction may be associated with significant alterations in myocardial levels of FFA (increase) or PE (decrease).

In Hungary, fat consumption is inadequate both from a quantitative and from a qualitative point of view. Statistical data also reveal that per capita consumption of fat has become stabilized and that within the vegetable fats/oils, margarine consumption increases year by year. To accelerate this process, a study was carried out on the effect of personal persuasion on the consumption of vegetable oils and different kinds of margarine. The results of this investigation are summarized in our paper.

The contamination of dietary fats and oils can have various origins: contamination of the raw materials that could not be eliminated by the industrial process; refining completely eliminates this type of contamination; contamination with one of the processing aids can occur if the process is not properly conducted; contamination with packaging materials will increase with the storage duration of the finished product (in the case of vinyl chloride monomer and styrene contamination); only the strict control and adequate choice of the materials and packaging conditions will allow complete elimination of this contamination type. The presence of small amounts of another fat (in vegetable margarines for instance) should also be mentioned although it is not a real contamination. The secondary reactions that may occur during the processing of dietary fats are primarily due to unwanted chemical reactions leading to the formation of fatty acid or native glyceride isomers (e.g. formation of geometric isomers during deodorization, formation of position isomers during hydrogenation). In the present stage of knowledge, it is fairly easy to avoid secondary reactions during deodorization, those that take place during hydrogenation are not yet under control, however.