Cravings: How junk food hijacks your brain

The reasons why you can’t resist those tasty snacks

Writer: Karolay Lorenty
Editor: Denis Duagi

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Many people couldn’t imagine a day going by without indulging on snacks that are a little less than healthy – an indispensable component of every social event. Crisps. Cookies. Chocolate. These foods have become a consistent part of our lives and we’re enjoying it. We can only wonder how they can be so delicious. The technical term is: hyperpalatable. What these foods have in common is their high levels of sugar, salt, fat and flavour, which surpass those found in healthier options, such as fruits and vegetables. This combination makes them irresistible, maybe, even addictive. 

With plenty of food available nowadays, we often eat out of pleasure rather than hunger, so called ‘hedonic eating’. But is it possible that our love for snacks has become uncontrollable? Experimentally, rats with extended access to hyperpalatable food experience a striking increase in weight. Not only do they consume twice as many calories, but also start seeking food compulsively when it is withdrawn, just like addicts looking for their next shot. Indeed, this behaviour corresponds with a dysfunction of the brain’s reward system, as that observed in cases of addiction. The increase in reward threshold is long-lasting, for at least 2 weeks, surprising when compared to the 48 hour effect of cocaine self-administration in rats. Even 1 hour of access to the hyperpalatable food results in binge-eating behaviour. How can these foods induce such addiction and loss of control over consumption?

As mentioned before, the reward system is involved. Obese individuals display greater activation of reward-associated brain regions when presented with visual food cues, triggering a strong desire to eat. But even if this is the case, why can’t we just stop ourselves? It can be explained by a concurrent reduction of the reflective system, which depends on the prefrontal cortex and is involved in decision-making and goal-driven behaviour. Specifically, there is reduced activation of the left dorsolateral prefrontal cortex, which plays a role in inhibitory control. There is a third system that may also participate: interoceptive awareness, which depends on the insular cortex, where the primary taste area of the brain resides. This system can simultaneously influence the activity of the other two, potentiating the craving while weakening self-control. 

But that’s not all, there is another factor that can influence food consumption: stress. Whether we’re guilty of indulging ourselves or just know someone that does it, we’re all familiar with the concept of ‘stress-eating’. With the concurring rise in obesity and stress-related disorders like anxiety in modern societies, this issue is particularly relevant. Chronic stress can exacerbate the binge-eating behaviour induced by hyperpalatable food in mice. Stress leads to a rise in cortisol levels, which in turn, can dysregulate the reward system by increasing dopamine release in one of the main reward centers of the brain, the nucleus accumbens. Dopamine stimulates the release of endogenous peptides resembling opioid drugs, consistent with increased expression of dopamine and opioid receptors in the nucleus accumbens of stress-eating mice. The dopamine and opioid-like peptides result in increased activity within the reward system, which prompts us to “self-medicate”, alleviating stress and improving our mood.

Taking into account the evidence supporting the similarities between the effects of junk food and drug consumption on the brain, as well as the devastating consequences of obesity, is it time to put in place more strict regulations? Or will we keep leaving it up to personal responsibility alone? It has been suggested to install policies on hyperpalatable foods similar to those for tobacco. Should we set restrictions on marketing? What about seeing photos of obesity’s consequences every time we buy sweets or go to a fast-food chain? Should we reduce the availability of junk food in vending machines and shops? Or can we simply imagine a world, where fruits or vegetables cost less than junk food?