Excess energy intake, in relation to expenditure, leads to weight gain and eventually to obesity.
Obesity is rapidly increasing in Western countries and is associated with an increased risk of several
diseases and a significantly higher mortality rate. Control of food intake consists of complex interplay
between the peripheral body and the central nervous system. The gastrointestinal tract secretes several
peptide hormones that participate in the control of feeding behaviour. The release of these peptides is
controlled by energy status and nutrients. In addition to food intake, gastrointestinal peptides control
digestion and gastrointestinal motility. This study investigated the effects of food components on the
release of gastrointestinal peptides and their effects on food intake.
Our everyday diet is rich in plant lectins, proteins with carbohydrate binding capacity. In this
thesis we showed that human gallbladder contraction was effectively stimulated by red kidney bean lectin
phytohaemagglutinin (PHA). Intraduodenal administration of PHA induced gallbladder contraction via a
cholinergic mechanism, without affecting peripheral plasma cholecystokinin (CCK) levels.
Dietary fibre is considered as a key element in a healthy diet. Postprandial glucose and insulin
lowering effects of fibre have been shown to be dependent on its viscosity. In this thesis we demonstrate
that viscosity also affects other postprandial gastrointestinal peptide responses and satiety. Interestingly,
lowviscous
oat bran beverage evoked higher satiety scores compared to otherwise similar but highviscous
beverage. This was in accordance with significantly increased releases of the hormones CCK, peptide YY
(PYY) and glucagon like peptide 1 (GLP1)
as well as the more efficiently suppressed ghrelin levels after
the consumption of the lowviscous
beverage compared to highviscous
one. Our results indicate that the
rheological properties of dietary fibre significantly affect the postprandial responses and satiety.
Spices, besides giving flavour to food, also induce thermogenesis and may affect satiety. Pungent
ingredients of wasabi, mustard oil and garlic are known to activate TRPA1 (transient receptor potential
ankyrin 1) channels. We found TRPA1 expression in mouse and human duodenum and revealed that
activation of these channels caused a robust increase in CCK secretion from the mouse intestinal
neuroendocrine cell line STC1
suggesting that these spices may improve digestion and affect satiety by
stimulating CCK release.
PYY, secreted from the ileum and colon, has been proposed to be a satiety peptide because it has
been shown to inhibit food intake in humans and in rodents. We performed proctocolectomy in rats in
order to create a surgical knockout
model for PYY. Colectomized rats were implanted with minipumps
delivering PYY(336)
or saline. In contrast to our expectations, colectomy increased rather than decreased
plasma PYY levels. In spite of significantly different plasma PYY levels between the treatment groups, no
difference in daily food intake or body weight gain was observed.
In conclusion, this thesis shows that components in our food significantly affect gastrointestinal
functions and peptide secretion. Thus by modulating the meal composition we may be able to affect food
intake and satiety.