Intraduodenal lipid modulates gastrointestinal motility and hormone release and suppresses energy intake more than does intraduodenal glucose.
Oral protein is the most satiating macronutrient and modulates postprandial glycemia.
The comparative effects of intraduodenal protein and lipid and their combined effects are unclear.
Dr Amy Ryan and colleagues from Australia investigated the effects of intraduodenal protein and lipid, alone or in combination, on antropyloroduodenal motility, gastrointestinal hormone release, glycemia, and energy intake.
The team evaluated 20 lean men on 5 randomized, double-blind occasions.
Antropyloroduodenal motility, cholecystokinin, glucagon-like peptide-1, insulin, glucagon, blood glucose, appetite, and nausea were measured during 90-min isocaloric intraduodenal infusions of lipid, protein, a 2:1 combination of lipid and protein combination of lipid and protein condition, or a control.
The doctors found that immediately after the infusion, energy intake from a buffet lunch was quantified.
|Intraduodenal infusions of lipid but not protein increased nausea|
|American Journal of Clinical Nutrition|
In comparison with the control, all nutrient infusions suppressed antral and duodenal and stimulated pyloric pressures.
Cholecystokinin and GLP-1 release and pyloric stimulation were lipid-load dependent, insulin and glucagon releases were protein-load dependent, and normoglycemia was maintained.
The team observed that intraduodenal infusions of lipid but not protein increased nausea.
Compared with the control, lipid and protein but not a 2:1 or 1:2 lipid:protein condition suppressed energy intake without major effects on appetite.
Dr Ryan's team concludes, "In lean men, despite differing effects on gut function, intraduodenal lipid and protein produce comparable reductions in energy intake."
"The effects of lipid may be a result of nausea."
"Protein also regulates blood glucose by stimulating insulin and glucagon."
"In contrast, at the loads selected, lipid:protein combinations did not suppress energy intake, suggesting that a threshold load is required to elicit effects."