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Junk Food Turns Rats into Food Junkies
4/5/2010
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New study affirms and expands on the alarming results of 2009 rodent study, and support a former FDA commissioner’s claim that junk food is literally addictive
by Craig Weatherby


Last year, former FDA commissioner David Kessler, M.D., published a book titled The End of Overeating, in which he proposed that junk foods create addiction-like cravings for more junk food.

He pointed to growing evidence that junky foodsfoods high in fat, salt and sugar but low in fiber and nutrientsalter the brain's chemistry in ways that compel people to overeat. 

As he told The Washington Post, “Much of the scientific research around overeating has been physiology… what's going on in our body. The real question is what's going on in our brain.”

Now, a study in rodents lends Kessler’s hypothesis some strong experimental support.

The results indicate that their development of obesity is caused by an alteration in brain chemistry linked to pleasure responses.

In fact, rats fed a junk-food-like diet developed the same brain chemistry changes seen when these animals consume heroin or cocaine.

These findings echo the results of a study published last year, in which rats became addicted to a junk food diet (Heyne A et al. 2009).

But the new study clarifies the connection to brain chemistry, and should prompt parents to protect children and lead health authorities to warn adults.

Rats fed junk food develop drug-like dopamine patterns
The new study was conducted by Dr. Paul Kenny and graduate student Paul Johnson from Florida’s Scripps Research Institute (Johnson PM, Kenny PJ 2010).

The goal was to test the effects of normal rat chow, versus a so-called “cafeteria-style” diet, which was defined as the kind of “palatable energy-dense food readily available for human consumption.”

In other words, the “cafeteria-style” diet provided foods high in fat, sugar, and salt and low in fiber and nutrients… stuff similar to the fare served in fast food chains and abundant in supermarkets’ grocery and freezer aisles.

They divided rats into three groups:
  • Group 1 was fed normal, healthful rat chow.
  • Group 2 had limited access to rat chow and limited access to the cafeteria-style diet. 
  • Group 3 had some access to rat chow, but extensive access to the cafeteria-style diet.
The results showed that the animals in Group 3 consumed twice the amount of calories as rats in the control (chow) group. 

Perhaps even more tellingly, the rats in Group 2
with limited access to the cafeteria-style dietconsumed more than two-thirds (66 percent) of their calories during the one hour they were given access to the cafeteria-style food. 

When the researchers removed the junk food from Groups 2 and 3 and tried to put those rats on a nutritious diet, they basically stopped eating entirely for two weeks, refusing to eat healthy food.

And the animals that showed the biggest “crash” in their brains’ pleasure-reward circuitries displayed the greatest shift in preference for the junky cafeteria diet.

In another part of the experiment, those same rats kept on eating the junky fare even when they anticipated being given an electric shock.

Disruption in dopamine system seen to create junk food junkies
Dopamine is a neurotransmitter that’s released in the brain by pleasurable experiences like food or sex or drugs like cocaine.

Accordingly, the researchers focused their attention on dopamine receptors in the brains of the animals, with specific attention on the dopamine D2 receptor.

Similar to the effects of cocaine, the junk food-fed animals displayed significant reduction in the activity of these D2 dopamine receptors.

Additional experiments tested the effects of knocking out these receptors using a specialized virus, and the results showed a dramatic acceleration of addiction-like eating.

The day after they provided access to the junk food, those animals began eating compulsively almost immediately, and their dopamine systems soon resembled those seen in animals that had been overeating junk food for several weeks.

As the authors wrote, “We found that development of obesity was coupled with emergence of a progressively worsening deficit in neural reward responses. Similar changes in reward homeostasis induced by cocaine or heroin are considered to be crucial in triggering the transition from casual to compulsive drug-taking.” (Johnson PM, Kenny PJ 2010)

They expressed their conclusion in dry scientific language; “Common hedonic [pleasure-drive] mechanisms may therefore underlie obesity and drug addiction” (Johnson PM, Kenny PJ 2010).

These sobering results provide the strongest support to date for David Kessler’s claim that people can literally become addicted to junk food.


Sources
  • Heyne A, Kiesselbach C, Sahún I, McDonald J, Gaiffi M, Dierssen M, Wolffgramm J. An animal model of compulsive food-taking behaviour. Addict Biol. 2009 Sep;14(4):373-83.
  • Johnson PM, Kenny PJ. Dopamine D2 receptors in addiction-like reward dysfunction and compulsive eating in obese rats. Nat Neurosci. 2010 Mar 28. [Epub ahead of print]

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