Junk Food Addiction Is All Too Real
Bijal Trivedi, New Scientist Magazine
Junk Food Addiction Is All Too Real
Is that cupcake a delicious indulgence or your next desperate hit?
Settled on the sofa watching the usual rubbish on TV, I notice that predictable, uncontrollable, nightly craving. At first, I sit there, fighting it. But the longer I fight, the worse it gets. After 20 minutes, I can't concentrate on anything, I feel anxious and start fidgeting. Finally, admitting my addiction, I break, go to the freezer and take a hit. Almost instantly, I relax, my brain in a state of bliss as the chemical courses through my veins. Isn't it amazing what a few scoops of ice cream can do?
Before you dismiss my agitation as mere weakness, consider this: To my brain, sugar is akin to cocaine. There's now compelling evidence that foods high in sugar, fat and salt -- as most junk foods are -- can alter your brain chemistry in the same way as highly addictive drugs like cocaine and heroin.
The idea, considered fringe just five years ago, is fast becoming a mainstream view among researchers as new studies in humans confirm initial animal findings, and the biological mechanisms that lead to "junk-food addiction" are being revealed.
Some say there's now enough data to warrant government regulation of the fast food industry and public health warnings on products that have harmful levels of sugar and fat. One campaigning lawyer claims there could even be enough evidence to mount a legal fight against the fast food industry for knowingly peddling food that is harmful to our health, echoing the lawsuits against the tobacco industry in the 1980s and '90s.
"We have to educate people about how their brains get hijacked by fat, sugar and salt," says
Arguably, it was the weight-loss industry that first introduced the idea to the public, long before there was any scientific evidence for it. For example, in her book "Lick the Sugar Habit," published in 1988, the self-confessed "sugarholic"
In 2001, intrigued by this nascent cultural phenomenon, neuroscientists
HOOKED ON SUGAR
Sugar is a key ingredient in most junk food, so they offered rats sugar syrup, similar to the sugar concentration in a typical soda beverage, for about 12 hours each day, alongside regular rat feed and water. After just a month on this diet, the rats developed behavior and brain changes that Avena and Hoebel claimed were chemically identical to morphine-addicted rats. They binged on the syrup and showed anxious behavior when it was removed -- a sign of withdrawal. There were also changes in the neurotransmitters in the nucleus accumbens, a region associated with reward.
Crucially, the researchers noticed that the rats' brains released the neurotransmitter dopamine each time they binged on the sugar solution, even after having eaten it for weeks (Neuroscience and Biobehavioral Reviews). That's not normal. Dopamine drives the pursuit of pleasure -- whether it's food, drugs or sex. It is a brain chemical vital for learning, memory, decision-making and sculpting the reward circuitry. You would expect it to be released when the rats eat a new food, says Avena, but not with one they're habituated to.
"That's one of the hallmarks of drug addiction," Avena says. This was the first hard evidence of a biological basis for sugar addiction, and sparked a slew of animal studies.
Those results were among the most exciting news in obesity research in the last 20 years, says
Since Avena and Hoebel's landmark study, scores of other animal studies have confirmed the findings. But it is recent human studies that have finally tipped the balance of evidence in favor of labeling a love of junk food as a proper addiction.
Addiction is commonly described as a dulling of the "reward circuits" triggered by the overuse of some drug. This is exactly what happens in the brains of obese individuals, says
In subsequent studies, Wang showed that even when (not obese) individuals are shown their favorite foods, an area of their brain called the orbital frontal cortex -- involved in decision-making -- experiences a surge of dopamine. The same area is activated when cocaine addicts are shown a bag of white powder. It was a shocking discovery that showed you don't have to be obese for your brain to exhibit addictive behavior. "I can tell they want it," says Wang.
Another critical leap in identifying junk food as addictive was made by
In an as-yet-unpublished study he found that when fed milkshakes, lean adolescents with obese parents experienced a greater surge of dopamine -- indicating a greater sense of satisfaction -- than those who had lean parents. Stice suspects that this is where the problem begins. "There are people born for whom eating is just more orgasmic," he says. It is this innate enjoyment of food that primes certain people to overeat.
Ironically, as they overeat, their reward circuitry dulls, which makes the food less satisfying and motivates them to eat more to compensate. They are essentially chasing the high of earlier heavenly eating experiences. This is precisely what we see with chronic alcohol or substance abuse, says Stice.
Stice has also shown that people with certain variants of the DRD2 and DRD4 genes are endowed with less active dopamine circuits, and as a result have a dulled dopamine response when eating appetizing foods. Paradoxically, this places them at greater risk of obesity than a person without those gene variants because it means they have to eat more to get a sufficiently rewarding level of dopamine release (Science).
Together, these studies suggest there are two routes to food addiction corresponding to overactive or underactive dopamine systems, respectively: one if you find food more rewarding than the average person, and another if it isn't rewarding enough.
Of course, fast food is more than just a sugar rush, it is often a rich cocktail of sugars, fats and salt. Neuroscientist
In animals, as in humans, repeated cocaine or heroin use dulls the brain's reward system. This leads to heavier use because the memory of a more pleasurable effect spurs the user to take more to get the same feeling, essentially chasing the high.
Kenny wondered whether rats that eat junk food would have a similar response to the cocaine-addicted rats he had already studied. He used three groups of rats. The first was a control group that only had access to standard rat feed. The second group could eat junk food -- bacon, sausage, icing and chocolate -- for only 1 hour each day with regular rat feed and water available for the rest of the time. The third group had an all-you-can-eat, around-the-clock buffet that included junk food and rat feed.
After 40 days, Kenny stopped access to the junk food in both experimental groups. The rats with unlimited access to junk food essentially went on a hunger strike.
"It was as if they had become averse to the healthy food," says Kenny. It took two weeks before the animals began eating as much as those in the control group.
Unlimited access to a powerfully addictive drug like cocaine has a big impact on the brain, says Kenny, so you might expect any addictive effect from food to be much less pronounced. But that is not the case. "Changes happened rapidly and we really saw very, very, striking effects. That's what surprised me."
The obese, unlimited junk food rats had dulled reward systems and were compulsive eaters. They would even tolerate electric shocks to their feet designed to deter them from eating junk food when the rat feed was still available shock-free. Cocaine-addicted rats behave the same way towards their drug.
When Kenny examined the brains of the obese rats with the unlimited junk food diet, they too had a dopamine deficiency in their striatum, similar to the obese individuals in Wang's study in humans. In the rats' brains, Kenny noticed there was a marked drop in a particular dopamine receptor, called D2. But it wasn't clear whether this drop affected a rat's propensity to become addicted to junk food.
To test the relevance of D2 receptors, he artificially reduced their number in the brains of a group of rats and then offered them only junk food for two weeks. The effect was dramatic. Compared to the control group offered the same diet, the reward circuitry in the brains of the modified rats showed a dulled response almost immediately.
Unlike normal rats, they gorged on junk food even when eating it was penalized with an electric shock. Crucially, rats with reduced D2 receptors fed only regular rat food did not show the same change in their reward circuitry (Nature Neuroscience). It seems there is an interaction between reduced D2 receptors and consumption of junk food that leads to addiction, says Kenny.
Taken together with Stice and Wang's results, this suggests that people who from birth have a low number of D2 receptors could also be prone to junk-food addiction. Kenny cautions that more studies in humans are needed before the conclusion can be generalized beyond rats.
Gold says there's plenty of evidence that food and drug addiction are so similar that treatments proven safe and effective for other addictions -- such as alcohol, nicotine, cocaine and heroin -- should be tested for food addiction, too.
"The real test of the 'hedonic eating' or food addiction hypothesis is if it can yield new and effective treatments," he says.
What some people claim is now beyond doubt is that junk foods rich in salt, sugar and fat switch on biological mechanisms that are just as powerful, and hard to fight, as drugs of abuse. Given that we regulate drugs because of the harms they can cause, is it time to begin tougher regulation of fast food, too?
Banzhaf believes there's now enough research for the
"The Health Consequences of Smoking: Nicotine Addiction," a report weighing in at over 600 pages, concluded that cigarettes were addictive, nicotine was the cause, and that the chemical and behavioral processes that define heroine and cocaine addiction were the same for tobacco.
"At that point, people began to accept it," Banzhaf says. But he acknowledges this is going to be a tricky fight. "Fast food isn't a (single) chemical so you can't meaningfully ask the question, 'Is a triple bacon cheeseburger addictive?'" he says. It would have to be something more specific about quantities of sugar, salt and fat.
"Long term, that's what's effecting public health. It's the healthy-looking kid who needs three Cokes a day, not the person who already weighs 400 pounds," he notes.
Signs of things to come can already be seen across the U.S. For example, trans fats were recently banned in restaurants in
Unsurprisingly, the food and drink industry is putting up a fight. These foods are only addictive to a "certain subset of consumers who don't exhibit the discipline required," says
Discounting waste, spoilage and returns, the food available to us today is about 30 percent higher in calories compared with 1970, says Cardello. He believes tax relief for companies producing low-calorie foods is one way to reduce calories consumed without destroying the companies that sell fast food.
Cardello says food companies don't design food to be addictive, but admits many products are designed for "high hedonic value", with carefully balanced combinations of salt, sugar and fat that, experience has shown, induce people to eat more.
Kessler points out that, of course, the ultimate power is in the consumers' hands. Individuals have a responsibility to protect themselves, he says. I can vouch for the fact that it is possible to break the habit. After two weeks of going cold turkey, I can report I have successfully kicked my ice cream habit. Now, if only I could kick my junk TV addiction."
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