|Table of Contents - Click to go to a section|
The most common eating disorder in our society is excessive eating
which includes craving and compulsive eating which can quite often result
in obesity (http://www.nutramed.com/zeno/addictive.htm#exorphins).
Obesity is a body condition where a person's body mass index is greater
than 30. Other diseases that can accompany or follow obesity include diabetes,
hypertension, and heart disease. Also, obese people are at a greater risk
of certain kinds of cancer like breast, colon, and uterine cancer. Nori
Geary, an associate professor of psychiatry at Cornell University, did
a great deal of work on the physiological control of feeding behavior (http://www.med.cornell.edu/rasp/gdir/geary.html).
Some people respond well to proper diet and exercise to overcome
obesity. For those who do not, however, antiobesity drugs are gaining popularity
in pharmaceutical compnaies. One potential antiobesity drug that was recently
developed by scientists in France and England is butabindide. This drug
works to regulate appetite by breaking down a neurotransmitter that signals
satiety. This drug has not yet been administered to humans, but its development
may provide information to help with the development of other antiobesity
drugs in the future (Jack 1756).
A number of biological and psychological factors are involved to consolidate energy intake, expenditure, and storage to satisfy specific biological or biophysiological processes. The degree to which these processes control eating behavior is regulated by sensors in the gastrointestinal tract, the liver, and the brain which all work to control this system through a process of positive and negative feedback system. Many forces, such as the taste of the food and the surrounding atmosphere, control the amount of food eaten. The receptors in the gastrointestinal tract manage the size and times of eating behavior while metabolic cues oversee energy consumption with respect to what the body needs. Overeating causes a greater amount of fat storage than did carbohydrate overfeeding. Studies of the appetites of obese women prove that energy intake during a high-fat lunch was much higher than during a high-carbohydrate lunch and this remained for the next 24 hours. The reason that has been hypothesized for this is that the metabolic rates of fats and carbos are different. Carbohydrates are more rapidly absorbed and contribute to the suppression of appetite. Fat storage, on the other hand, is almost without limit with a lower satiety calibre. Carbohydrate storage in the body, in the form of glycogen, is limited, and need to be constantly refilled. Obesity is a disorder that is related to a "disease" of the fat storage mechanisms and if a person is obese, there will be a presence of lipids already in the small intestine that delay the emptying of gastric fluids. These fatty acids in the stomach relax the stomach and therefore, cause the stomach to be able to adapt to a greater capacity of food. When the stomach receptors are stimulated, the gastric sensitivity is transformed to accommodate a meal while the positive sensations of enjoyment are also aroused so that this experience is repeated again. Studies have shown that people show feelings of sleepiness and enjoyment while fat is in the intestines demonstrating the significance of the association between eating and contentness (Read 1-3).
Appetite is controlled in the brain by way of a series of signals
triggered by dietary breakdown and by autonomic signals produced by distension
of the stomach and intestines (Jack 1756). All of these signals combined
are processed by complex interactions by the neuronal networks and neurotransmitters.
Among the most important of the neurotransmitters is cholecystokinins (CCK)
that are a family of hormonal and neuronal peptides that link the stomach
and the brain. CCK is also involved in appetite control by producing a
satiety signal in response to food intake. CCK has been found to be low
in some women with bulimia, causing them to binge (http://www.bixler.com/brainnet/eatingdi.html).
Also, when essential amino acids, especially phenylalanine, are present
around the stomach, the release of CCK increases (Aceto 97). Studies have
also shown that CCK sensitivity changes with age as well (Rolls, Dimeo,
and Shide 931).
The question in studying the CCK system is whether human food intake
can be regulated by controlling this system. Studies with rats have shown
that CCK may act by increasing the sensitivity of the stomach to distension.
However, this same study was conducted with humans and the results were
slightly different; the release of CCK in humans desensitizes the gastric
afferent neurons maybe by acting at the same level as the brain stem (Read
6). Another observation that challenges this notion that CCK regulates
satiety is that the data on humans is not consistent unlike the data on
animals (Read 6). It seems that gastric distention by itself does not cause
the normal comfortable feeling of satiety; distension combined with duodenal
lipid infusion perhaps is related to some effect of the lipid on the central
processing of the afferent details (Read 6).
In terms of oral administraion of this neurotransmitter to help maintain
food intake to minimum, CCK is rapidly broken down in the gastrointestinal
tract before it can be absorbed. Intravenously, CCK administration also
failed because it is short-lived due to peptidase digestion. So, instead
of trying to raise levels of CCK externally, scientists are trying out
new ways to block the breakdown of endogenously produced CCK to cut back
on food intake (Jack 1756).
The process involved in this reaction is as follows: scientists have
recognized a stomach enzyme (serine pepidase) that digests CCK with little
to no effect on other neuropeptides involved in the control of gallbladder
contraction, gastric emptying, and intestinal mobility. If CCK were used
to overcome hunger, this might illustrate the observation that infusion
of lipid into the duodenum slowed the rate of ingestion (Read 8). Michael
Lean, a professor of nutrition at Glasgow University, said "'Appetite
is the most fundamental and potent life-force of all. It is unlikely to
be regulated by a single system or common pathway. The CCK patha dramatic
effect on appetite or energy balance (Jack 1756).'"
CCK as an appetite suppressant could appear to look convincing if
it were not for the experiments showing that certain CCK antagonists have
not shown a convincing effect on the eating patterns in humans. Other hormones
including bombesin, gastric inhibitory polypeptide, glycogen-like insulino-tropic
peptide, and pancreatic glucagon may also alter satiety, but the data showing
that these hormones really have an effect is not persuasive enough (Read
Aceto, Chris. (1996) Fat Burners. Joe Weider's Muscle and
Fitness. 57: 90-100.
Jack, David. (1996) Fighting Obesity the Franco-British Way.
The Lancet. 347: 1756-1758.
Read, Prof. (1994) The Role of the Gut in Regulating Food Intake
in Man. Nutrition Reviews. 52: 1-9.
Rolls, B., Dimeo, K., amd Shide, D. (1995) Age-Related Impairments
in the Regulation of Food Intake. The American Journal of Clinical
Nutrition. 62: 923-935.
Psychology DepartmentThe Health Psychology Home Page is produced and maintained by David Schlundt, PhD.
Vanderbilt Homepage | Introduction to Vanderbilt | Admissions | Colleges & Schools | Research Centers | News & Media Information | People at Vanderbilt | Libraries | Administrative Departments | Medical
|Return to the Health Psychology Home Page|
|Send E-mail comments or questions to Dr. Schlundt|