The physical state and the spatial distribution of fat within the gastric lumen during digestion are critical factors influencing the rate of fat delivery to the small intestine. This will affect the rate of fat absorption and metabolism and the signalling between the gut and brain. Fat digestion commences in the mouth with the secretion of acid lipase from salivary glands, which is particularly important in infants and those with pancreatic insufficiency.
Acid lipase from the salivary gland and from the gastric fundus act within the stomach causing approximately 10% of dietary triacyl glycerides to be hydrolysed to fatty acids. Together with gastric phospholipid and dietary emulsifiers, these fatty acids facilitate the formation of emulsions with particle size 1-10 μm suitable for the action of pancreatic lipases.
Intragastric lipolysis is an important determinant of gastric emptying.
The intracellular fat component of a test meal empties with the solid phase of a meal, whilst a liquid fat component that is free from the solid phase of the meal empties much more slowly than the aqueous phase of the meal.
Marciani et al in previous studies have shown that acid-stable emulsions stimulate greater cholecystokinin release and are associated with delayed gastric emptying, compared with acid-unstable emulsions. The mechanism for these differences is uncertain. Stable emulsions, which do not break under acid conditions, present a larger surface area for lipolysis, which may cause greater concentrations of fatty acids to reach the duodenum, where they can exert their satiating effect both by acting on fat-sensitive enteroendocrine cells, and by delivering lipid-laden chylomicrons into the venous and lymphatic systems.
Acid-unstable emulsions in which the fat layer empties after the aqueous phase, deliver fat with a markedly reduced interface area. Since the lipolysis takes place almost exclusively at the fat-aqueous interface, lipolysis products are likely to be created more slowly in the duodenum and upper small bowel.
Marciani et al have shown that it is possible to delay gastric emptying and increase satiety by stabilising the intragastric distribution of fat emulsions against the gastric acid environment.
This raises fascinating possibilities for cooking.
Marciani et al 2009 Effect of intragastric acid stability of fat emulsions on gastric emptying, plasma lipid profile and post prandial satiety. British J Nurtion vol 101 pp 919-928

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