Gastric physiology and function: effects of fruit juices

The stomach stores food and starts digesting protein and fat. Lipids, sugars, certain amino acids, and nutrients of high osmolality trigger sensory mechanisms from the intestine which inhibit gastric emptying. Food rich in carbohydrates leaves the stomach slower than protein-rich food, and emptying is slowest after a meal containing lipid. For carbohydrate beverages, the gastric emptying rate is primarily determined by the volume, caloric content, and osmolality of fluid ingested. Gastric emptying rates vary among isocaloric beverages of different type (e.g., sucrose, fructose, galactose) or forms (e.g., maltodextrins, starches) of carbohydrate. For instance, gastric emptying is faster for a fructose solution compared with isocaloric glucose and galactose solutions. A maltodextrin or a sucrose solution empties faster than a glucose solution. This is possibly due to the greater inhibitory feedback associated with the introduction of glucose in the duodenum. In addition, fruit juices contain soluble fibers which further modulate the gastric emptying. Noninvasive methods to study gastric emptying have recently been developed. The pattern of the myoelectric activity of the gastric contraction and the effect of meals on this pattern can now be recorded by cutaneous electrodes. In healthy children ingesting different juices, the myoelectric pattern of the stomach (indicator of the gastric emptying) correlates with the carbohydrate absorption (measured by breath hydrogen excretion). Fast gastric emptying was associated with greater production of breath hydrogen. The malabsorption of juice carbohydrates may in part be related to their effect on gastric motility.