Within-day variation of lipolytic activity in human milk

Milk was collected from six mothers during their 8th wk of lactation to determine the diurnal variation of bile salt-stimulated lipase and serum-stimulated lipase. On the day of collection, one breast was completely emptied at 0600, 1000, 1400, 1800, and 2000 h. Activities of bile-stimulated lipase and serum-stimulated lipase in the milk were determined. Activity of bile-stimulated lipase was constant throughout the day, whereas serum-stimulated lipase activity varied significantly with time. Both activities differed significantly in milk from different women. Time of collection must be considered when measuring activity of serum-stimulated lipase but is not a major variable when measuring activity of bile-stimulated lipase in human milk. These results may be helpful when designing future studies involving these enzymes.