Research Review: Is food addiction real? | Precision Nutrition

Research Review: Is food addiction real?

By Helen Kollias, Ph.D.


Is it just me or does everybody seem to have some sort of addiction these days?

Addictions used to be limited to drugs like alcohol, cocaine and heroin, but now there are new addictions: shopping addictions, TV addictions, tattoo addictions…

And each addiction has its poster celebrity. (According to one shrink, Jesse James is a “sex addict” and Sandra Bullock is a “love addict”.)

But are these real addictions or just an excuse for not having self control?

In the last week a new study about food addiction has been all over the news, but are you getting the whole story?


Food addiction

You need to eat food to live. Thus your brain makes eating rewarding. Have you ever had a particularly yummy meal after being famished? Did you feel happier, more content?

Research question

We know from research that food provides pleasure and how that works [1], but the study in this week’s review had pretty compelling evidence that junk food is addictive in ways similar to cocaine and heroin.

Johnson PM, Kenny PJ. Dopamine D2 receptors in addiction-like reward dysfunction and compulsive eating in obese rats. Nat Neurosci. 2010 Mar 28.


Since the study was done on rats I have to include the usually non-human disclaimer that because we’re not rats the results can’t be 100% applied to humans, but it’s the best we got.

For this study there were three groups:

  1. Group 1 – no access to junk food; ate only healthy rat chow.
  2. Group 2 – 1 hour of access to junk food and unlimited access to rat chow.
  3. Group 3 – 18-23 hours of access to junk food and unlimited access to rat chow.

What was the junk food? Goodies like bacon, sausage, cheesecake, pound cake, frosting and chocolate. (From personal experience I can tell you rats love chocolate, so forget trying to catch rats with cheese. Go with chocolate.)

After the 40 days were up the rats were only given rat chow for 2 weeks. (Think of it as a cleanse.)

Figuring out addiction: electric shock technique

How do you know if a rat is addicted?

Well for this study they used a specific brain (neural) stimulation technique.

With this technique, the researchers could figure out whether the rats needed more electrical stimulation to get the feeling of satisfaction or reward. For those of you interested, the technique is called brain stimulation reward.

This technique is similar to the scene on The Simpsons where a cupcake is connected to the mild electrical current. There’s a sign that says, “Do not touch.”

Bart sees the cupcake. Bart sees the sign. He tosses it aside and goes for the cupcake. He gets shocked, goes for the cupcake again, and gets shocked – this goes on repeatedly.

The rats are trained by being punished by electrical shock in a specific part of their cage (paired with a light). They would get a shock every time the light went on.

Then the next day the rats were given access to junk food and had the lights turned on. Normally, rats run away from the part of the cage where they got the shock the day before.



Lots of access to junk food mean lots of weight gain

Rats with nearly unlimited access to junk food gained more weight than rats without any access to junk food, or just an hour of access to junk food.

Not only did unlimited junk food access make these rats bigger, it depressed their brain’s reward function. That means that the rats need more stimulation — in this case junk food — to get the same reward or high as they got in the beginning of the 40 day experiment.

This is pretty strong evidence proving that junk food is addictive.

Even 1 hour of access to junk food changes eating habits

Since rats with 1 hour access to junk food and rats with no access to junk food weighed the same after 40 days you’d think that moderation is the key to junk food, but not quite.

I was shocked by this: in 1 hour the rats ate 66% of their calories from the junk food to which they had access, and for the other 23 hours they ate 33% of their calories from rat chow. Rats with unlimited access got 95% of their calories from junk food!

Even after 2 weeks junk-food-free rats were still addicted

After 40 days were up the rats went on a 2 week cleanse without any junk food.

The good news is that the fat unlimited junk food rats lost nearly as much weight as they gained in 40 days, but the bad news is the rats basically stopped eating.

On Day 1 the rats ate pretty much nothing. After 2 weeks, they gradually started eating about half the calories they should be eating (take a look at figure 1).

Figure 1 food addiction
Figure 1 – Rats were put on a junk food free diet for 14 days following 40 days of either rat chow only, restricted access to junk food (1 hour/day) or extended access to junk food (18-23 hours/day). Notice the huge plunge in calories in the extended group that stays way below normal. Figure 3b from Johnson PM, Kenny PJ. Nat Neurosci. 2010 Mar 28.

More bad news: they still had suppressed brain reward function — meaning they were still addicted.

Electric shock doesn’t deter addicted rats from junk food

Rats addicted to junk food were also trained to be afraid of the light, but if junk food was available they’d stick around and eat even when the lights were turned on.

Doesn’t sound too bad? Big deal! Rats ate junk food with the lights on! Well, this particular technique is also used to identify cocaine-taking behaviour in rats [2]. In other words, rats will avoid normal fear to take cocaine… or eat food.

Dopamine receptors decreased in obese rats

Obese rats had less of a specific type of dopamine receptor (D2). This is the same receptor that is reduced in drug-addicted people.


Almost unlimited access to junk food (bacon, sausage, cheesecake, pound cake, frosting and chocolate) led to a lot more weight gain in rats — about 25% more over 40 days.

While an hour of access to junk food a day didn’t cause weight gain, it did mean the rats ate most of their calories from junk food.

After 40 days on junk food the rats became addicted and 2 weeks of cleansing didn’t break the addiction. Compare that to rat cocaine addiction, where after 48 hours researchers found improvement in their addiction.

Yup, food addiction may be harder to shake than cocaine addiction [3].

The researchers didn’t say if more fatty junk food (like bacon) was eaten or more sugary junk food (like frosting) was eaten, so there is no way of figuring out if addiction was triggered by excessive saturated fat , sugar or both.

Whether fat or sugar is causing the addiction, the researchers figure the change in the brain during food addiction is similar to cocaine and heroin addiction.

Bottom line

A lot of access to junk food, both high fat and high sugar, alters brain function that leads to addiction. This study provides compelling evidence that food addiction is real.


Click here to view the information sources referenced in this article.

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