Lipids dietary fats

Dietary fats, libers, and other carotenoids have been reported to interfere with carotenoid bioaccessibility. It is clear that by their presence in the gut, lipids create an environment in favor of hydrophobic compounds such as carotenoids. When arriving in the small intestinal lumen, dietary fats stimulate bile flow from the gallbladder and therefore enhance the micelle formation, which in turn could facilitate the emulsification of carotenoids into lipid micelles. Without micelle formation, carotenoids are poorly absorbed a minimum of 3 g of fat in meal is necessary for an efficient absorption of carotenoids, except for lutein esters that require higher amounts of fat. ... 

The full effect of changes in coffee consumption on serum cholesterol does not occur as quickly as it does to changes in dietary fat intake. Typically, when a stable high-saturated fat diet is replaced with a stable low-saturated fat diet, the maximum changes in serum lipid levels are achieved in two to four weeks.29 30 The serum lipid response to changes in coffee consumption does not appear to reach its full effect until after four weeks or more. 

Orlistat induces weight loss by lowering dietary fat absorption, and it also improves lipid profiles, glucose control, and other metabolic markers. Soft stools, abdominal pain or colic, flatulence, fecal urgency, and/or incontinence occur in 80% of individuals, are mild to moderate in severity, and improve after 1 to 2 months of therapy. Orlistat interferes with the absorption of fat-soluble vitamins and cyclosporine. 

The physiological functions of carboxylesterases are still partly obscure but these enzymes are probably essential, since their genetic codes have been preserved throughout evolution [84] [96], There is some evidence that microsomal carboxylesterases play an important role in lipid metabolism in the endoplasmic reticulum. Indeed, they are able to hydrolyze acylcamitines, pal-mitoyl-CoA, and mono- and diacylglycerols [74a] [77] [97]. It has been speculated that these hydrolytic activities may facilitate the transfer of fatty acids across the endoplasmic reticulum and/or prevent the accumulation of mem-branolytic natural detergents such as carnitine esters and lysophospholipids. Plasma esterases are possibly also involved in fat absorption. In the rat, an increase in dietary fats was associated with a pronounced increase in the activity of ESI. In the mouse, the infusion of lipids into the duodenum decreased ESI levels in both lymph and serum, whereas an increase in ES2 levels was observed. In the lymph, the levels of ES2 paralleled triglyceride concentrations [92] [98],... 

Dietary fat consists essentially of mixed triglycerides. These fatty lipids pass through the stomach into the small intestine without much change in structure. In the small intestine, triglycerides are partly hydrolyzed by an enzyme (lipase) that leads to the formation of oil-water emulsion. 

The regular digestion of dietary fats and fat-soluble substances and/or their absorption via the lipid route is compromised in the frame of various diseases such as cystic fibrosis, short bowel syndrome, cholestasis, and chronic inflammatory bowel diseases. 

FIGURE 5.7 Absorption of dietary fat-soluble substances via the lipid route affected by insufficiently emulsified and micellised lipids. 

A. Dietary fats are packaged by the enterocytes into chylomicrons, a very large type of lipid-protein complex or lipoprotein, for export to other organs. 

Vitamin A absorption from the small intestine requires dietary fat and pancreatic lipase to break down retinyl esters and bile salts to promote the uptake of retinol and carotene. Drugs, such as mineral oil, neomycin and cholestyramine, that can modify lipid absorption from the gastrointestinal tract can impair vitamin A absorption. The use of oral contraceptives can signihcantly increase plasma vitamin A levels. 

Awad, T. B. and J. P. Chattopadhyay. Effect of dietary fats on the lipid composition and enzyme activities of rat cardiac sarcolemma. J Nutr 1983 113(9) 1878-1883. 

CN133 Oliveros, L. B., A. M. Videla, and M. S. Gimenez. Effect of dietary fat saturation on lipid metabolism, arachi-donic acid turnover, and peritoneal macrophage oxidative stress in mice. Braz J Med Biol Res 2004 37(3) 311-320. 

CN160 Kalra, S., S. Mahmood, ]. P. Nagpaul, and A. Mahmood. Changes in the chemical composition of surfactantlike particles secreted by rat small intestine in response to different dietary fats. Lipids 2002 37(5) 463-468. 

CN201 Trautwein, E. A., A. Kunath-Rau, J. Dietrich, S. Drusch, and H. F. Erbersdobler. Effect of dietary fats rich in lauric, myristic, palmitic, oleic or li-noleic acid on plasma, hepatic and biliary lipids in cholesterol-fed hamsters. Br J Nutr 1997 77(4) 605-620. 

The relationship between diet and cancer risk is extremely complex (7). Factors that appear to enhance carcinogenesis under one set of conditions may have no effect or even inhibit carcinogenesis under different conditions (2). The link between dietary fat and cancer is complicated by many factors, in particular total calorie intake and fatty acid composition (2). Among the fatty acids that comprise lipid, only linoleic acid is clearly linked to the enhancement of carcinogenesis in rat manunary gland (5), pancreas (4) and colon (5). 

Yordy, J.R. Alexander, M. (1981) Formation of N-nitrosodiethanolamine from diethanolamine in lake water and sewage. J. environ. Qual, 10, 266-270 Zeisel, S.H. (1996) Choline. A nutrient that is involved in the regulation of cell proliferation, cell death and cell transformation. In Hebver Kritchevsky, eds. Dietary Fats, Lipids, Hormones and Tumorigenesis, New York, Plennm Press, pp. 131-141... 

VLDLs to fat and muscle tissue. The NADPH necessary for lipid synthesis is obtained by oxidation of glucose in the pentose phosphate pathway. Excess amino acids are converted to pyruvate and acetyl-CoA, which are also used for lipid synthesis. Dietary fats move via the lymphatic system, as chylomicrons, from the intestine to muscle and fat tissues. 

Increased synthesis of fatty acids De novo synthesis of fatty acids from acetyl CoA in adipose tissue is nearly undetectable in humans, except when refeeding a previously fasted individual. At other times, fatty acid synthesis in adipose tissue is not a major pathway (see Figure 24.5, G). Instead, most of the fatty acids added to the lipid stores of adipocytes are provided by dietary fat (in the form of chylomicrons), with a lesser amount is supplied by VLDL from the liver (see p. 229). 

Carrol, R.M. and Rudel, L.L. 1981. Dietary fat and cholesterol effects on lipoprotein cholesterol ester formation via lecithin-cholestrol acyltrans-ferase (LCAT) in vervet monkey. J. Lipid Res. 22 359-363. 

Ostos MA, Lopez-Miranda J, Ordovas JM et al. Dietary fat clearance is modulated by genetic variation in apolipoprotein A-IV gene locus. J Lipid Res. 1998, 39 2493-2500. 

Weinberg RB, Geissinger BW, Kasala K et al. Effect of apolipoprotein A-IV genotype and dietary fat on cholesterol absorption in humans. J Lipid Res. 2000, 41 2035-2041. 

J. M. Laher, M. W. Rigler, R. D. Vetter, J. A. Barrowman, and J. S. Patton, Similar bioavailability and lymphatic transport of benzo(a)pyrene when administered to rats in different amounts of dietary fat, J. Lipid. Res. 25 1337-1342 (1984). 

If lipid oxidation is a factor in promotion of tumorigenesis by dietary fat, one might expect the process to be inhibited by dietary antioxidants. This topic is discussed in more detail elsewhere in this symposium (28 ), but the results have not provided clear-cut answers to the question. Some of the synthetic antioxidants such as butylated hydroxytoluene (BHT) appear to inhibit the promotion of tumorigenesis by dietary fat, but results with vitamin E, a naturally-occurring antioxidant, have been largely negative (29). 

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