Fat digestion in the neonate
- Department of Child Health, Royal Hospital for Sick Children, Yorkhill Hospitals, Glasgow
- Mr William Manson, Department of Paediatric Surgery, Royal Hospital for Sick Children, Edinburgh EH9 1LF.
Fats are essential components of the diet, and have a critical role in the growth and development of the neonate. Far from being simply compact sources of energy (providing 40-50% of calorie requirements), they are also integral constituents of neural and retinal tissues.1 2 Dietary fats come in three forms: triacylglycerols; phospholipids; and cholesterol esters, all of which contain fatty acids esterified to alcohols.
The infant consumes fats largely as triacylglycerols, which need to be broken down by enzymes in the upper gastrointestinal tract before absorption. Compared with adults, however, the newborn infant’s exocrine pancreas is “immature,” secreting only small amounts of lipase even in response to secretagogues.3 4 How the neonate digests fats, and what part they play in neurodevelopment5 is of growing importance, particularly when preterm infants of ever shorter gestation are surviving into adulthood.
Structure, nomenclature and properties of fatty acids
Fatty acids are composed of carbon–carbon (C–C) chains with a carboxylic acid group (-COOH) at one end and a methyl group (-CH3) at the other. The longer the C–C chain, the more concentrated the energy source, but the more difficult the fatty acid is to metabolise. Human milk contains predominantly medium and long chain fatty acids (C:10 to C:22), but other foods contain fatty acids with longer and shorter chains.
Fatty acids are named according to the number of carbon atoms which form the chain and the number of double bonds between them. Thus palmitic acid, which has 16 carbon atoms and no double bonds, is 16:0. Alternatively, the Greek derivation is used—hexadecanoic acid. The carbon atoms are labelled from the carboxylic acid end (fig 1). Either the carboxyl carbon is labelled C1, followed by carbons C2, C3, C4, etc. in sequence, or the first carbon after the carboxyl group is labelled …
