The macronutrients carbohydrate, protein and fat are known to regulate digestive physiology via the release or suppression of a number of specific gut hormones. The physiological effects of the hormones include alterations to satiety, gastric emptying and gut motility, changes which can have pronounced effects on subsequent energy intake. There is evidence to suggest that lipolysis is necessary before fat is able to exert its effects and stimulate physiological changes in the gut. This is likely because it is not triglycerides, but fatty acids that trigger the gut response. Inhibition of lipase enzymes decreases lipolysis and this in turn prevents fatty acids from releasing gut hormones, delaying gastric emptying or affecting subsequent energy intakes. It has been suggested that decreasing the fat droplet size in emulsions may increase gut response to fat because of the increased rate of fatty acid production.
Researchers1 have investigated the effects of fat droplet size on gut function by infusing fat emulsions of different sizes into the duodenum of 10 healthy male volunteers. The results showed that as fat droplet size increased, the suppression of the pressure waves from the antrum of the stomach and the duodenum decreased, and stimulation of the basal and pyloric pressures increased. This suggested that smaller droplets decreased gut motility to a greater degree that larger droplets. In addition, as droplet size increased stimulation of plasma triglyceride decreased, suggesting a reduction in the rate of chylomicron formation. Cholecystokinin and peptide YY both showed inhibited release in response to larger fat droplets, suggesting that appetite was suppressed more by smaller droplet. Overall, the results highlight the importance of fat digestion in gut function and support the evidence for fatty acid regulated gut control.
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