Fat Utilization

The ability of an animal to utilize fats for growth has been reported to be dependent on the nature of the dietary carbohydrate. When weanling rats were given diets high in lactose, Boutwell, Geyer, Elvehjem 

A considerable wealth of information is available on the general chemistry of these substances but precise structural knowledge is still lacking and a wide field of research awaits the activities of the chemist. This field not only covers carbohydrate and protein chemistry, but the area lying between the two, and it also borders on the lipid field. 

All compounds have a precise and often highly specific function to fulfil, and in animals many of them are concerned also with the protection of the body against agents of disease. The problems of immunity and of enzyme systems involve the consideration of protein-carbohydrate complexes so that structural studies in the group now need to be undertaken seriously. 

It is not proposed to include the better known polysaccharides or the plant gums in the group because they can be conveniently classified separately. It must be pointed out, however, that some of these may occur naturally in firm combination with protein as instanced by the shock effect observed when solutions of crude inulin are injected into animals and by the reported isolation of desmoglycogen and glycogen combined with myosin.  

In this classification of the compounds into mucopolysaccharides, mucoproteins, and mucolipids, it must be emphasized most strongly that since the mode of isolation of any naturally occurring high polymer influences profoundly its composition and biological properties, the difference between divisions is not always sharp and there may be some degree of overlapping. 

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One suggestion to explain this discrepancy is that two pathways of fat catabolism are available and that ketone body formation is the resultant of only one type of breakdown.177 This latter type, also called the indirect fat utilization, 182 occurs in the liver the catabolism of fat in the muscle, called the -direct method, either involves no ketogenesis or the ketone bodies are immediately utilized and no accumulation occurs. 

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. 

D. B. Allen, Sustained benefit after 2 years of growth hormone on body composition, fat utilization, physical strength and agility, and growth in Prader-Willi syndrome. J Pediatr, 2000.137(1) 42-9. 

Wiseman (1986) reported a reduction in digestibility and in available energy of up to 30% due to oxidation of fat as a result of overheating during processing. A number of naturally occurring fatty acids can also adversely affect overall fat utilization. Two such components are erucic acid present in rapeseed oils and some other Brassica spp., and the cyclopropenoid fatty acids present in cottonseed. 

Katongole, J.B.D. and March, B.E. (1980) Fat utilization in relation to intestinal fatty acid binding protein and bile salts in chicks of different ages and different genetic sources. Poultry Science 59,819-827. 

Poultry. Lecithin has nutritional application in poultry feeds. The caloric value of lecithin (8900 kcal/kg) for broilers was reported to be greater than tallow (5000-7000 kcal/kg) or soybean oil (8800 kcal/kg) (332). This research was complementary to earlier observations that fat utilization and metabolizable energy value were improved when lecithin was also included in chick diets (333, 334). Phospholipids can increase pigment absorption contributing to egg yolk pigmentation (335). Nutrition also plays a key role in the value of meat. Brazilian research found that lecithin in the diets of broilers improved the sensory scores for breast meat (336). 

Fatty Acids Synthesis, Elongation, and Desaturation. The main objective of feeding fats to animals is to provide a concentrated energy source, not to have the fat stored in the tissues. Recognized EFA requirements are no more than several percent of dry matter at the most, but the critical roles they play in maintaining the metabolic machinery has attracted the majority of current research on dietary fat utilization. 

Hawley, J.A., Brouns, F, and Jeukendrup, A. Strategies to enhance fat utilization during exercise. Sports Med. 25, 241-257, 1998. 

In vivo deuterium ( H) MRS has been used to characterize amino acid metabolism, body iron content, brain and kidney metabolism and body fat utilization rates in rodents. These studies rely on the use of deuterium labelling or the existence of natural-abundance deuterium in water or lipids. For example, deuterium-labelled methionine was used to confirm the dominant contribution of the glycine/ sarcosine shuttle to the metabolism of excess methionine, while deuterium-labelled glucose was used to show that systemic glucose level influences brain... 

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