Fat, absorption

Energy production from triacylglycerols starts with their hydrolysis into free fatty acids and glycerol. Enzymes called lipases, which catalyze the reaction, carry out this hydrolysis. 

The reaction releases the three fatty acids and glycerol. An intestinal carrier absorbs the glycerol, which will eventually rejoin with fatty acids in the intestinal cells. 

The bile salts form the edge of the micelle and also appear, in fewer numbers, dispersed throughout the inside of the micelle. The lipids exist in a bilayer on the inside of the disc. Bile acids are important for fatty acid absorption. Fat-soluble vitamins (A, D, E, and K) absolutely require bile acids for absorption. 

The mixed micelle provides a large surface area for the action of pancreatic lipase, which is responsible for the majority of digestive 

Bile-acid metabolism explains the ability of certain kinds of dietary fiber to help lower serum cholesterol. A molecule of bile acid circulates through the liver and intestine five or more times before finally being eliminated. Soluble fiber (such as that found in oat bran) binds bile acids, but itself cannot be absorbed. Therefore, fiber-bound bile acids are eliminated in the stool. Because bile acids derive from cholesterol, synthesizing more bile acid drains the body s stores of cholesterol, which leads to a reduction in serum cholesterol, and therefore, to a lower risk of coronary artery disease. Eating oat fiber cannot overcome an excessive dietary cholesterol consumption, of course. In other words, consuming excessive amounts of well-marbled steak and expecting to overcome the effects by eating a bran muffin would be foolish. 

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Oilseed proteins are used as food ingredients at concentrations of 1—2% to nearly 100%. At low concentrations, the proteins are added primarily for their functional properties, eg, emulsification, fat absorption, water absorption, texture, dough formation, adhesion, cohesion, elasticity, film formation, and aeration (86) (see Food processing). Because of high protein contents, textured flours and concentrates are used as the principal ingredients of some meat substitutes. 

The symptoms of vitamin E deficiency in animals are numerous and vary from species to species (13). Although the deficiency of the vitamin can affect different tissue types such as reproductive, gastrointestinal, vascular, neural, hepatic, and optic in a variety of species such as pigs, rats, mice, dogs, cats, chickens, turkeys, monkeys, and sheep, it is generally found that necrotizing myopathy is relatively common to most species. In humans, vitamin E deficiency can result from poor fat absorption in adults and children. Infants, especially those with low birth weights, typically have a vitamin E deficiency which can easily be corrected by supplements. This deficiency can lead to symptoms such as hemolytic anemia, reduction in red blood cell lifetimes, retinopathy, and neuromuscular disorders. 

There has been considerable focus on the development of drugs that lead to a reduction in the total amount of adipose tissue. These include agents targeted at limiting fat absorption, the inhibition of appetite, and the stimulation of energy expenditure (thermogenesis)-or a combination thereof. The best example of drugs,... 

Effect Reduced fat absorption Appetite suppression Appetite suppression, peripheral actions... 

Vitamins are organic nutrients with essential meta-bohc functions, generally required in small amounts in the diet because they cannot be synthesized by the body. The hpid-soluble vitamins (A, D, E, and K) are hydrophobic molecules requiring normal fat absorption for their efficient absorption and the avoidance of deficiency symptoms. 

The food, now in a liquid form known as chyme, passes through the pyloric sphincter into the duodenum, where stomach acid is neutralized. There is wide variation in lengths of the components of the small intestine (i.e., duodenum, jejunum, and ileum) between individuals (Table 98-1). Most absorption of digested carbohydrate and protein occurs within the jejunum. Most fat absorption occurs within the jejunum and ileum. In the small bowel, breakdown of macronutrients (i.e., carbohydrate, protein, and fat) occurs both within the lumen of the gut and at the intestinal mucosal membrane surface. The absorptive units on the intestinal mucosal membrane are infoldings known as... 

The protein ingredients reduce fat absorption while potato starch improves shelf life by retaining moisture. 

Commercial bakeries and doughnut shops normally use a system that extrudes a batter from a reservoir directly into the deep fat fryer (Figure 5). In such a system the rheology of the batter is vitally important. The batter must flow and spread as needed. The major influence on the batter viscosity is the water content, which is around 70% of the flour or around 40% of the dry mix. Various gums are sometimes added to the dry mix to bind water, reduce fat absorption, and control the viscosity. Examples of these gums are guar gum, locust bean gum and carboxymethyl cellulose. 

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. 

B12. Berkowitz, D., Croll, M. W., and Shapiro, B., A critical evaluation of isotopic lipid techniques to measure fat absorption. Gastroenterology 40, 667 (1961). 

In the studies discussed, wheat bran, cellulose, and psyllium fiber feeding resulted in increased fecal fat losses and in lowered blood serum cholesterol and triglyceride levels (14,15,32,41) as well as increased fecal losses of calcium. Possible involvement of dietary fat with high or low dietary fiber intake has not been extensively investigated. However, that calcium is involved in intestinal fat absorption is generally accepted (42-45). 

In steatorrhea, the formation and precipitation of insoluble calcium soaps formed from calcium and fatty acid has been generally credited as the cause of reduced calcium and fat absorption. 

Fat absorption has been found to be less efficient in infants than in adult humans (60-63). Thus, the potential for formation and precipitation of calcium soaps inhibiting the absorption of calcium would appear to be greater. Furthermore, formulation of products to best promote both fat and calcium utilization by bottle fed infants would appear to be a desirable, obtainable objective. 

Several studies have been conducted on calcium-fat interactions in human infants (64-70). Low synthesis of bile salts and low pancreatic lipase activity may be responsible for poorer fat utilization in infants than in adults (63,71). Fat from infant formulas may be lower than that from human milk because of the lack of a bile-stimulated lipase in the former (72). In infants, fat absorption tends to decrease with increase in fatty acid length, with lower degree of saturation, and with increase of total fat (3). Triglyceride structure may also influence fat absorption in the infant and, thus, indirectly, might also affect calcium absorption in the infant. 

Factors negatively affecting absorption of dietary fat may also be expected to negatively affect absorption of calcium. In the normal, healthy adult, dietary fat absorption is very efficient. However, such factors as level of dietary fat, fatty acid chain length, degree of fatty acid saturatedness, or triglyceride structure may have a measurable effect on calcium absorption under some circumstances. 

Cake Donuts. The effects of 0-30% substitution of dry-roasted air-classified navy, pinto or black protein flour for wheat flour on the physical and sensory qualities of cake donuts were investigated. In general, fat absorption decreased as the level of substitution increased with the pinto bean variable having the lowest values. An increase of navy bean and pinto protein levels decreased donut height after the 10% level. The donuts with pinto bean protein exhibited less spread than the other bean type donut variables. Navy bean protein produced a more tender donut than the other bean types. The control donut and those with navy bean protein were the lightest in color, followed by pinto and black bean protein donuts,... 

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],... 

Wolfe has presented an excellent description of the systematic application of stable and radioactive isotope tracers in determining the kinetics of intestinal fat absorption, hepatic triglyceride synthesis, lipid mobilization, triglyceride-fatty acid recycling, and cholesterol turnover. 

Malabsorption Because they sequester bile acids, these resins may interfere with normal fat absorption and digestion and may prevent absorption of fat-soluble vitamins such as A, D, E, and K. 

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