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About the value of controlling appetite • NutrInsight
Table 1: Hormones of satiety and of hunger (adapted from 61)
Brain imaging,
the way forward
Hedonic inputs
ROLE
Hormones of hunger Hormones of satiety
NAME
Ghrelin
Cholecystokinin Enterostatin Glucagon-like peptide-1 Peptide YY
Insulin Leptin
LOCATION
Stomach, Duodenum, Ileum, Caecum, Colon
Duodenum, Jejunum, Colon Intestine
Ileum, Colon
Ileum, Colon
Pancreas
Adipose tissue, Stomach
Non-invasive brain imaging techniques,
such as positron-emission tomography
(PET) and functional magnetic resonance
imaging (fMRI) scanning, have given us
a clearer understanding of the central Hypothalamus regulation of appetite.
PET scanning has confirmed that the hypothalamus is involved in regulating
appetite, and demonstrated that the
prefrontal cortex may also be involved Adipose tissue in satiety. The advantage of fMRI
scanning over PET scanning is that it
is able to pinpoint more accurately
which area of the brain is activated. In
particular, it has demonstrated that PYY3-36 obese sujects display a delayed OXM response by the hypothalamus to the
DVC Ghrelin
CCK
Meal timing
Meal size
Energy expenditure Reproductive competence
Nutrient receptors
Vagal afferents
Stretch receptors
Chemosensors
Leptin
Insulin
GLP-1 action
ingestion of glucose, thus providing Pancreas fresh information to help us understand problems affecting the regulation of the appetite (5). Using these exploratory
brain imaging techniques is undoubtedly the way forward.
Incretin
Figure 5: Neuro-physiological regulation of food intake (adapted from 17)
To conclude, the regulation of appetite appears to be extremely complex (a combination of internal, external, physiological and psychological factors), and it is sometimes difficult to understand or predict the effects of one meal compared to those of another. The subjective appetite is not always correlated to the food consumed; the hormones involved in regulating appetite are sometimes also involved in other control systems or interact with one another, which restricts the pertinence of using them in isolation as a biomarker of appetite. Furthermore, subjective and objective approaches do not answer the same questions, and the limitations of each of these methods can be offset by other methods to provide a body of evidence. It therefore seems to be self-evident that the various methods should be combined to elucidate the short- and long-term regulation of appetite.
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