Novel lipid sources in parenteral and enteral nutrition

Abstract

Lipids are an important energy source in the parenteral and enteral nutrition of critically41 patients because of their high energy density (37-6kJlg) and low osmolarity, although in conventional parenteral nutrition only the recently available 300 g lipid emulsions (12.5 MJA) are more energy dense than 700 g dextroseA (9.6 MJA) as starting components in total parenteral admixtures, e.g. 200g lipid at 8-3MJA and 1OOg lipid at 4.2MJA. Lipids also serve as a source of two fatty acids, a-linolenic and linoleic, that are essential in human nutrition at less than 0-5 % and about 1-0 % total energy respectively; however, up to 4 % of energy as linoleic acid will further improve N utilization. Fat-soluble vitamins (A, D, E, K) and other important nutrients which have not been established as being essential (i.e. carotene, lycopene, flavonoids) have improved absorption in the presence of fats. Man is unable to desaturate long-chain fatty acids at either C-3 (a-linolenic) or C-6 (linoleic) from the methyl end (a-C) but can at C-9, a situation that results in three common families of fatty acids in human metabolism n-3, n-6, and n-9. a-Linolenic acid (18:3n-3) thus serves as the precursor for eicosapentaenoic acid (20:4n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA) and linoleic (1 8:2n-6) for dihomo-y-linolenic acid (20:3n-6; DHLA) and arachidonic acid (20:4n-6; AA) after elongation of the C chains and further desaturation but preservation of their n-3 or n-6 identity. These latter compounds have unique importance in that they serve as precursors for the eicosanoids (EPA, DHLA, AA) which are ubiquitous second messengers or have unique effects (DHA in vision and brain function, AA as a second messenger) in addition to their properties as polyunsaturated fatty acids. These three families of fatty acids have numerous interrelationships which have considerable clinical impact. For example, a-linolenic acid can be converted in man to EPA or DHA but with limited efficiency (Meydani et al. 1993) which makes this a less-rapid and effective means of increasing the EPA content of membranes. Although alinolenic acid inhibits the elongation and desaturation of linoleic acid to DHLA and AA,

Overfeeding fat as monoglyceride or triglyceride: effect on appetite, nutrient balance and the subsequent day's energy intake

“…In terms of chemical structure, the fatty acid is mainly found on the 1-position of the glycerol backbone. Positions 1 and 3 are hypothesised to be least readily absorbed, in comparison to position 2 which is more readily absorbed (Bistrian, 1997). It is therefore possible that the 2-monoglyceride may exert differential effects on appetite and feeding behaviour; (v) The present study is of a relatively short-duration.…”

“…Total energy intake on day 2 therefore amounted to 2.056RMR. The position of the fatty acid will affect the absorption of the fat, as it is more ef®ciently absorbed in the 2 position than in the 1 or 3 position (Bistrian, 1997). Dimodan is a 1 position monoester, made from edible vegetable oil, which has a high polyunsaturate content.…”

High and low carbohydrate and fat intakes: limits imposed by appetite and palatability and their implications for energy balance

“…Therefore while the degree of saturation (Lawton et al, 1997) and chain length of orallyingested dietary fat can have signi®cant effects on appetite and EI, these data suggest that orally ingested 1-monacyl glycerols did not differentially in¯uence appetite and EI relative to triacylglycerols. It is possible that 2-monacyl glycerols may exert a greater appetite suppressing effect since these molecules are more readily absorbed across the gut wall (Bistrian, 1997). The effects of varying the fatty acid composition of triglycerides (structured lipids) is currently unknown.…”

Structural identification of triacylglycerol isomers using electron impact excitation of ions from organics (EIEIO)

“…The physiological role of TAGs is to serve as a reserve of fatty acids for energy generation via -oxidation. However, these same stored fatty acids may also serve as precursors, either directly or indirectly, to bioactive oxidized metabolites such as eicosanoids that play a key role in mediating the cell-signaling pathways that control inflammation (1). High levels of TAG in plasma have been implicated in a host of pathophysiologies, including arteriosclerosis, nonalcoholic fatty liver disease, and metabolic syndrome (2).…”