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Obesity as an addictive behavior




Enviado por Felix Larocca



  1. The experience of
    pleasure
  2. How does it
    happen?
  3. What"s going on in the
    brain during cravings?
  4. Are particular foods more
    reinforcing than others? Why?
  5. Are certain people at
    greater risk for drug or food addictions?
  6. Does the overlap between
    addiction and obesity reveal any new targets for
    treatment?
  7. In summary
  8. Bibliography

To some people, especially for those who have been treated for
substance dependencies, excessive eating may be lingering
manifestations of their addictive behaviors and tendencies.

Neuroimaging reveals a shared basis for
"chocoholism", sugar cravings and drug addiction

Evidence shows that compulsive eating and
drug abuse engage some of the same brain circuits in similar
ways, offering a new angle for understanding and treating
obesity.

The question being, how do foods and drugs
affect the brain in the same way?

The system in the brain that both drugs and
food activate is basically the circuitry that evolved to reward
behaviors that are essential for our survival. One of the
reasons why humans are more attracted to certain foods is because
of their rewarding, pleasurable properties. 

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The experience of
pleasure

When we experience pleasure, our brains
learn to associate the gratifying experience with the cues and
conditions that predict it. In other words, the brain remembers
not just what the food tasted like but also the sensation of
pleasure itself, and the cues or behaviors that preceded it. That
very memory becomes stronger and stronger as the cycle of
predicting, seeking and obtaining pleasure becomes more reliable
— creating a reflex pattern or vicious circle. When you
remember that food, you also automatically expect the pleasure
that derives from it. So when you like something very much, the
mere fact of being re-exposed to it, even if it is out of reach,
will trigger the desire to get it.

In scientific terms, we call this process
conditioning.  

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Conditioned cues or memories are very
powerful and can profoundly affect our behavior. And when
conditioning occurs to a positive stimulus, such as the taste of
food, you are much more likely to repeat a particular action to
obtain it. Drugs, such as tobacco, alcohol or sugar are
particularly effective as conditioning stimuli, primarily by
virtue of their chemical properties. They can directly stimulate
areas of the brain involved with pleasure in a way that is more
efficient than natural reinforcers, such as food or sex. You get
an exaggerated response (supraphysiological) partly because the
drug can get to the brain very fast, in a matter of
seconds. With natural reinforcers the process of activating
the reward pathway is more prolonged. Importantly, the
conditioning that takes place links the behavior not just to the
stimulus itself but to the environment and other cues that might
have been only peripherally associated with it.

That"s why; avoiding the environment where
the cycle is awakened is such a good idea.

Advise: Do not enter that kitchen at
night!

How does it
happen?

It happens, because that"s exactly what
Nature intended: if the behavior necessary to seek a pleasurable
experience was triggered exclusively by the object, the
conditioned response would be very ineffective indeed.

Think about the need to find food to
survive, for example: say we are primitive creatures in the
jungle and you by pure chance taste a banana. The banana tastes
good, but if you were just conditioned to remember that it tasted
good — and nothing of the smell, the shape, the color, or the
location of the banana — your ability to find it again would be
deficient. Once you create this conditioned memory, though, it"s
just like Pavlov"s dogs; the response becomes a reflex. This
conditioned response underlies both the drive in drug addiction
and the drive in compulsive eating.

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What"s going on
in the brain during cravings?

Had Pavlov been able to peer inside the
dog"s brain, he would have very likely seen that there is an
increase in dopamine in the brains of those dogs when they get
exposed to the sound previously paired with the meat. Dopamine
tells us what's important — the unexpected bits of new
information we need to process in order to survive, like alerts
about sex, food and pleasure, as well as danger and pain. Indeed
they have been tested in humans using brain imaging technologies.
The human brain is highly sensitive to food stimuli. Proof exists
that when people are shown favorite foods, to which they have
been conditioned, there is an increase in dopamine in the
striatum which is a brain region involved with reward and
behavioral motivation. This increase is just from smelling and
looking at the food, because during experiments participants are
told that they will not be able to eat it.

And this is the very same neurochemical
response that happens when addicts see a video of other people
taking drugs, or anything to do with their drug of choice, like
where they normally take it or with whom they take it.

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Brain Reward System

Also in the brains of both drug addicts and
obese people is typically found a reduced number of D2 dopamine
receptors in the striatum, compared to non-abusers and non-obese
controls, respectively. Perhaps these findings reveal that the
brain is somehow trying to compensate for the repeated surges in
dopamine stimulation from continuous stimulation with drugs or
food.  Another possibility is that these individuals
had lower numbers of receptors initially, a biological feature
that overall may put them at increased risk for diseases of
addiction. Experiments show that low numbers of D2 receptors
are well documented in people addicted to cocaine, alcohol,
opiates and other drugs. Interestingly, a recent study found
the same type of relationship between the availability of D2
receptors and Body Mass Index (BMI) in obese individuals. In
other words, the more obese a person is, the fewer receptors they
have. By contrast, in normal weight subjects, the levels of D2
receptors are not associated with their BMI.

Now the chronic use of drugs — by
repeatedly stimulating the dopamine and other systems —
eventually leads to a disruption of function in frontal cortical
areas involved with inhibiting behaviors and emotions. It is also
possible that this circuit is weaker in people who are addicted
to drugs from the start, but this has not been
established. In obesity, however, there is no evidence that
the frontal cortex is similarly disrupted. What has been
documented instead is that the drive for food is so powerful that
it overrides any ability to exert inhibitory control.

Are particular
foods more reinforcing than others? Why?

High calorie foods—particularly foods
that are high in fat or sugar — are more likely to trigger
compulsive eating. Again, that makes sense from Nature"s
perspective. As hunters, we didn"t always succeed at finding
something to eat and so high-calorie foods, which pack a lot of
energy, offered a survival advantage. In that environment, it was
in our best interest to consume as much of this type of food as
we could find. So they are very reinforcing. But today when we
open up our refrigerators, we have a 100 percent chance of
succeeding at finding essentially that very kind of
food.

Our genes have changed little, but in our
environment, we are now surrounded by high-fat, high-sugar foods.
And this abundance is undoubtedly a major factor contributing to
the rise in obesity. Conditioning responses are incredibly
powerful especially with food: when one goes past a vending
machine and see chocolates one likes very much, one desire that
chocolate even though one is not hungry. But if those chocolates
weren"t there, it would be the last thing to enter the
mind.

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Are certain
people at greater risk for drug or food
addictions?

We know from twin studies that
approximately 50 percent of the risk for both addiction and
obesity is genetic and environmental. But the genes involved come
into play on many different levels — from differences in the
efficiency with which people metabolize drugs (or food) to
differences in the likelihood of engaging in risk-taking or
exploratory behaviors to more specific risks, such as the
underlying sensitivity of the reward system.

In obesity, some people may be at a greater
risk for compulsive eating because they may be overly sensitive
to the rewarding properties of food. One study showed that some
obese people have increased brain activity in response to mouth,
lip and tongue sensations. For them, eating may be much more
pleasurable than other natural reinforcers. Likewise, some people
are not very efficient at registering or responding to internal
signals of satiety, so they are possibly going to be more
vulnerable to cravings triggered by food cues in their
environment.

For example, in a recent study it was
looked at obese people who had an Implantable Gastric Stimulator
(IGS), which electrically activates the vagus nerve and causes
the stomach to expand and feel full. And even with this implant,
these people still only manage to lose about five percent of
their body weight. On a higher level, they have powerful
conditioned responses that can apparently override other
regulating signals.

This finding has repercussions for those
that seek in the stomach bypass operation a solution for their
obesity!

Does the overlap
between addiction and obesity reveal any new targets for
treatment?

There are pharmacological interventions to
explore, such as medications that increase the dopamine response
in the brain. Rimonabant, which boosts dopamine levels by
dampening the endocannabinoid system, has shown promise in
helping people who are obese and those who are
smokers.

But, at this point these findings are
nothing more than tentative.

Another exciting development is the recent
synthesis and preliminary testing of an orally administered drug
that blocks orexin, a peptide that reinforces the "high"
associated with drinking alcohol and is thought to regulate
feeding. This drug could be extremely helpful in the treatment of
specific brain disorders that involve aberrant food and drug
taking behaviors. Also, because of the stigma associated with
both of these conditions, obesity and drug addiction can lead to
a deep sense of isolation, which is very stressful. This is an
area where group therapy could help.

Yet another exciting area NIDA is
researching is the use of functional magnetic resonance imaging
(or fMRI) in biofeedback to train people to exercise specific
parts of their brains, just like muscles. At Stanford University,
neuroscientists have similarly trained healthy subjects and
chronic-pain sufferers to control their brain activity to
actually modulate their experience of pain. So NIDA is exploring
the possibility that one might use this kind of biofeedback to
train people to control a region of the brain called the insula,
which has been implicated in food and drug cravings. Smokers who
have a lesion in the insula after a stroke, for instance, seem to
lose the desire to smoke.

But one of the major and distinct obstacles
for a person trying to recover from compulsive eating is the
obvious fact that one has to eat in order to survive whereas, if
one is addicted to an illegal substance, one is, in a way
protected, by the fact that that drug is not going to be
environmentally available everywhere. One of the therapeutic
interventions for drug addicts is to teach them to avoid places
associated with their habit. But how do you do that with food?
It"s impossible.

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A good measure would be to steer clear from
the places where the "fix" is found — as avoiding the kitchen,
to avoid the food cravings.

And these people do suffer. In
rats, it has been shown that, if they receive a very high-sugar
diet and then an opioid antagonist (naloxone) is administered,
that this action can trigger a withdrawal that is similar to the
one observed when naloxone is administered to an animal that has
received repeated injections of morphine. This indicates that
chronic exposure to high sugar diets generates physical
dependence. If similar processes happen in humans then
interventions to mitigate the appearance of withdrawal symptoms
during dieting may benefit the discomfort to the subject and
improve outcomes.

In
summary

Addiction is not a choice. It is a
reflexive response. Do you think that Pavlov"s dogs had a choice
of salivating when they heard the sound that had been conditioned
to the meat? They did not and had you seen inside their brains
you would probably have observed that the sound would trigger
dopamine increases in their striatum that would be signaling to
expect the reward of the meat. The message that one gets when
dopamine is liberated in striatum — in this case, the dorsal
striatum — is that one needs to get into action to achieve a
certain goal. It is a powerful motivator. It is extremely hard to
overcome these impulses with sheer willpower.

That"s why I say: To lose weight is
like learning another language…

Bibliography

  • Larocca, F: (1984) The Psychiatric
    Clinic of North America issue on Eating Disorders
    W. B.
    Saunders & Co.

  • Larocca, FEF: Losing Weight: A
    Balancing Act
    in monografías.com

  • Larocca, F. E. F: (2007) El Sistema
    Fiduciario
    en monografías.com

  • Dwyer, J and Larocca, F. E. F: (1974)
    When a Child is too fat. Patient Care
    VIII-6- 158-76

  • Cassell, D, and Larocca, F. E. F:
    (1994) The Encyclopedia of Obesity and Eating
    Disorders.
    Facts On File

  • Larocca, F. E. F: (1991) A Public
    Primer on Eating and Mood Disorders
    Midwestern
    Medical

  • Larocca, F. E. F: (1986) Eating
    Disorders: Effective Care and Treatment
    Ishiyaku
    Euroamerica

  • Larocca, F. E. F: (1986) Eating
    Disorders: The Facts
    in New Directions for Mental
    Health Services
    # 31 Jossey-Bass

  • Larocca, F. E. F: (1986) Una
    Introducción a las Disorexias
    en
    Médico Interamericano 5:12 27-30

  • Larocca, F. E. F: (2007) Los
    Trastornos Malignos del Comer
    en Psikis.com y en
    monografías.com

  • Microsoft Encarta 2007
    (CD/DVD) List of recommended reading

 

 

Autor:

Dr. Félix E. F.
Larocca

 

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