I think everyone pretty much knew that about junk food. Those that really get a first hand look at it are people that have essentially lived off junk food and decide to cut it out cold turkey and go through the same withdrawal symptoms that people go through when they cut off a drug, alcohol, coffee, soda, etc.
This study used rats as the subjects for 40 days and they broke the rats into three groups:
1. One group was fed healthy rat food (I guess whatever "healthy" means to a rat..)
2. A second group was fed healthy rat food, but also given junk food that they could munch on for only an hour a day.
3. The third group could eat as much junk food that they wanted, 23 hours a day.
Shockingly, the third group that could eat all the junk food that they wanted, became obese fairly quickly.

But the interesting part is how their brains changed.
By monitoring implanted brain electrodes, the researchers found that the rats in the third group gradually developed a tolerance to the pleasure the food gave them and had to eat more to experience a high.
The researchers also added a little pain into each of the groups when food was present. When that pain was administered, the rats in the first two groups were frightened away from eating, while the rats in the third group didn't care, they were solely focused on eating that junk food.
This relates fairly closes to studies done on rats involving cocaine and heroin:
In previous studies, rats have exhibited similar brain changes when given unlimited access to cocaine or heroin. And rats have similarly ignored punishment to continue consuming cocaine, the researchers note.
When relating this to humans:
The ingredients in purified modern food cause people to "eat unconsciously and unnecessarily," and will also prompt an animal to "eat like a drug abuser [uses drugs]," says Wang.
It appears that the main culprit in all of this is the neurotransmitter, dopamine that rats (and humans) have:
The neurotransmitter dopamine appears to be responsible for the behavior of the overeating rats, according to the study. Dopamine is involved in the brain's pleasure (or reward) centers, and it also plays a role in reinforcing behavior. "It tells the brain something has happened and you should learn from what just happened," says Kenny.
Overeating caused the levels of a certain dopamine receptor in the brains of the obese rats to drop, the study found. In humans, low levels of the same receptors have been associated with drug addiction and obesity, and may be genetic, Kenny says.
How do we get past this addiction?
With continued research like this, there's always the possibility that treatments can be developed to stop the decrease of dopamine that is associated with the addiction.
There's also the practical applications of:
1. Slowly cutting bad food out and replacing them with healthier choices or
2. Just cold turkey throwing out all the junk food and going healthy (although this is the more extreme approach and can result in a withdrawal period, I tend to like this one the best. Get it over with).
But we probably need to look a little further into it to determine the "Why?" of the addiction, just like it's necessary when working with someone with a drug or alcohol addiction.
In other words, maybe people are using that junk food as a substitute for something else, and maybe digging deeper into that realm will help with getting away from the addiction of food, permanently.
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