Fat, dietary

Kalbus, G. E. Lieu, V. T. Dietary fat and Health An Experiment on the Determination of Iodine Number of fats and Oils by Goulometric Titration, /. Chem. Educ 1991, 68, 64—65. 

Bde salts, cholesterol, phosphoHpids, and other minor components are secreted by the Hver. Bile salts serve three significant physiological functions. The hydrophilic carboxylate group, which is attached via an alkyl chain to the hydrophobic steroid skeleton, allows the bile salts to form water-soluble micelles with cholesterol and phosphoHpids in the bile. These micelles assist in the solvation of cholesterol. By solvating cholesterol, bile salts contribute to the homeostatic regulation of the amount of cholesterol in the whole body. Bile salts are also necessary for the intestinal absorption of dietary fats and fat-soluble vitamins (24—26). 

The rising incidence of obesity has not paralleled sucrose consumption. The FDA Task Force concluded that sugars have no unique role in obesity and that dietary fat rather than carbohydrate is a significant contributor to this condition (62,67,68). However, sugar can promote weight gain in individuals with life-styles marked by excess caloric intake and insufficient exercise. 

Dairy products (see Milk and milkproducts) have been staple items of the diet for many centuries, and have long been the target for imitation. The development of nutritional guidelines emphasizing the need to reduce total dietary fat, dietary cholesterol [57-88-5] C2yH4 0, and saturated fatty acids (see Fats and fatty oils Fat substitutes), has increased the interest in imitation dairy foods. However, with the exception of butter and cream the market penetration of dairy substitutes has been limited. 

Possibly the most serious nutrition problem in the United States is excessive food consumption, and many people have experimented with fad diets in the hope of losing excess weight. One of the most popular of the fad diets has been the high-protein, high-fat (low-carbohydrate) diet. The premise for such diets is tantalizing because the tricarboxylic acid (TCA) cycle (see Chapter 20) is the primary site of fat metabolism, and because glucose is usually needed to replenish intermediates in the TCA cycle, if carbohydrates are restricted in the diet, dietary fat should merely be converted to ketone bodies and excreted. This so-called diet appears to work at first because a low-carbohydrate diet results in an initial water (and weight) loss. This occurs because... 

Ester hydrolysis is common in biological chemistry, particularly in the digestion of dietary fats and oils. We ll save a complete discussion of the mechanistic details of fat hydrolysis until Section 29.2 but will note for now that the reaction is catalyzed by various lipase enzymes and involves two sequential nucleophilic acyl substitution reactions. The first is a trcinsesterificatiori reaction in which an alcohol gioup on the lipase adds to an ester linkage in the tat molecule to give a tetrahedral intermediate that expels alcohol and forms an acyl... 

Amide hydrolysis is common in biological chemistry. Just as the hydrolysis of esters is the initial step in the digestion of dietary fats, the hydrolysis of amides is the initial step in the digestion of dietary proteins. The reaction is catalyzed by protease enzymes and occurs by a mechanism almost identical to that we just saw for fat hydrolysis. That is, an initial nucleophilic acyl substitution of an alcohol group in the enzyme on an amide linkage in the protein gives an acyl enzyme intermediate that then undergoes hydrolysis. 

Answers questions and offers suggestions for ways to reduce dietary fat intake. 

Various authors The cholesterol facts. A summary of the evidence relating dietary fats, serum cholesterol, and coronary heart disease. Circulation 1990 81 1721. 

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. ... 

Jayaranjan, P., Reddy, J.P. and Mohanram, M., Effect of dietary fat on absorption of (3-carotene from green leafy vegetables in children, Indian J. Med. Res., 70, 53, 1980. 

Increased body mass index (especially in women) Higher dietary fat intake Light-colored irides Increased exposure to sunlight... 

Reduced dietary fat intake associated with high-fiber diets... 

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. 

Mathews-Roth M. M. and Krinsky N. I. (1984). Effect of dietary fat level on UV-B induced skin tumors, and anti-tumor action of beta-carotene. Photochem Photobiol 40(5) 671-673. 

Excessive dietary fat (calories) General increase in incidence of... 

It is well appreciated that dietary fat retards proximal gastrointestinal transit. For hydrophobic drugs with low aqueous solubility, dissolution becomes the rate-limiting process the appreciation that fat might increase bioavailability by increasing time available for dissolution and that mixed triglycerides often provide a better solvent than aqueous media has not been lost on formulation scientists. 

Dietary fats are required for carotenoid uptake by intestinal cells. Fats have an important role in the continuation of the process of carotenoid absorption, because the human intestine is incapable of secreting significant quantities of chylomicrons into the bloodstream in the absence of fats (Ornelas-Paz and others 2008b). Some studies have suggested that at least 5 g/day of dietary fat are required for suitable (3-carotene absorption (West and Castenmiller 1998), whereas others suggested the consumption... 

Omelas-Paz JJ, Failla ML, Yahia EM and Gardea-Bejar AA. 2008b. Impact of the stage of ripening and dietary fat on in vitro bioaccessibility of (1 carotene in Ataulfo mango. J Agric Food Chem 56 1511-1516. 

Familial lipoprotein lipase deficiency is characterized by a massive accumulation of chylomicrons and a corresponding increase in plasma triglycerides or a type I lipoprotein pattern. Presenting manifestations include repeated attacks of pancreatitis and abdominal pain, eruptive cutaneous xanthomatosis, and hepatosplenomegaly beginning in childhood. Symptom severity is proportional to dietary fat intake, and consequently to the elevation of chylomicrons. Accelerated atherosclerosis is not associated with this disease. 

Treatment of type I hyperlipoproteinemia is directed toward reduction of chylomicrons derived from dietary fat with the subsequent reduction in plasma triglycerides. Total daily fat intake should be no more than 10 to 25 g/day, or approximately 15% of total calories. Secondary causes of hypertriglyceridemia should be excluded, and, if present, the underlying disorder should be treated appropriately. 

Type V hyperlipoproteinemia requires stringent restriction of dietary fat intake. Drug therapy with fibrates or niacin is indicated if the response to diet alone is inadequate. Medium-chain triglycerides, which are absorbed without chylomicron formation, may be used as a dietary supplement for caloric intake if needed for both types I and V. 

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