In this comprehensive review of gall bladder physiology, it states that
In the digestive period strong gallbladder contractions and sphincter
of Oddi relaxation lead to the high rates of bile discharge flowing
into the common bile duct and duodenum. During this period, the
gallbladder motor activity like the rest of the gastrointestinal tract
is influenced by the three phases of digestive process: cephalic,
antral, and duodenal [16]. The cephalic phase is initiated by stimuli
that activate the central nervous system, as individuals are exposed
to olfactory, visual, and the taste of food. This phase is mediated by
preganglionic vagal fibers that synapse with postganglionic
cholinergic neurons. It is estimated that as much as 30–40% of the
gallbladder bile may be emptied during this phase. Once food reaches
the stomach it triggers an antral-gallbladder reflex also mediated by
vagal fibers. The gallbladder empties most of its remaining contents
during the intestinal phase induced by the release of CCK from the
duodenum and proximal jejunum [1]
so that even just seeing or smelling food can cause 30-40% of the bile to be released into the duodenum. The rest of the gallbladder contents are emptied under neuroendocrine control.
Meals containing proteins and fats act on duodenal CCK containing
endocrine cells that stimulate vagal sensory fibers followed by
activation of pre- and postganglionic cholinergic neurons [1]
The above mixture includes oil, so it would act via the second part of this mechanism, but there is nothing in the known physiology to suggest it would be better than a meal.
References:
[1] Jose Behar, “Physiology and Pathophysiology of the Biliary Tract: The Gallbladder and Sphincter of Oddi—A Review,” ISRN Physiology, vol. 2013, Article ID 837630, 15 pages, 2013. doi:10.1155/2013/837630
[16] I. Takahashi, M. K. Kern, W. J. Dodds et al., “Contraction pattern of opossum gallbladder during fasting and after feeding,” American Journal of Physiology, vol. 250, no. 2, pp. G227–G235, 1986. View at Scopus