|Can you resist? (Shuttershock)|
I always have. My friend and fellow graduate student Andrew is equally afflicted, and living in Hershey, Pennsylvania—the “Chocolate Capital of the World”—doesn’t help either of us.
But Andrew is braver than I am. Last year, he gave up sweets for Lent.
Are you abstaining from sweets for Lent this year, too? Here’s what you can expect over the next 40 days.
Sugar: natural reward, unnatural fix
In neuroscience, food is something we call a “natural reward.” In order for us to survive as a species, things like eating, sex, and nurturing others must be pleasurable to the brain so that these behaviors are reinforced and repeated.
The process of evolution has resulted in the mesolimbic pathway, a brain system that deciphers these natural rewards for us. When we do something pleasurable, a bundle of neurons called the ventral tegmental area uses the neurotransmitter dopamine to signal to the nucleus accumbens. The connection between the nucleus accumbens and our prefrontal cortex (PFC) dictates our motor movement, such as deciding whether or not we're going to take a bite of that delicious chocolate cake. The PFC also activates hormones that tell our body, “Hey, this cake is really good! And I’m going to remember that for the future.”
|The brain's reward system (blue). NIDA (Wikimedia Commons)|
Fruit is one thing, but modern diets have taken on a life of their own. It’s estimated that the average American now consumes 22 teaspoons of added sugar per day, amounting to an extra 350 calories. Today, with convenience being more important than ever in our food selections, it’s almost impossible to come across processed and prepared foods that don’t have added sugars for flavor, preservation, or both.
These added sugars are sneaky—and unbeknownst to many of us, we’ve become hooked. In ways that drugs of abuse—like nicotine, cocaine, and heroin—hijack the brain’s reward pathway and make users dependent, increasing neurochemical and behavioral evidence suggests that sugar is addictive, too.
Sugar addiction is real
“The first few days are a little rough,” Andrew told me about his sugar-free adventure last year. “It almost feels like you’re detoxing from drugs. I found myself eating a lot of carbs to compensate for the lack of sugar.”
There are four major components of addiction: bingeing, withdrawal, craving, and cross-sensitization (the notion that one addictive substance predisposes someone to become addicted to another). All of these components have been observed in animal models of addiction—for sugar, as well as drugs of abuse.
Like drugs, sugar spikes dopamine release in the nucleus accumbens. Over the long-term, regular sugar consumption actually changes the gene expression and availability of dopamine receptors in both the midbrain and frontal cortex. Specifically, sugar increases the concentration of a type of excitatory receptor called D1, but decreases another receptor type called D2, which is inhibitory. To add insult to injury, regular sugar consumption inhibits the action of the dopamine transporter, a protein which pumps dopamine out of the synapse and back into the neuron after firing.
In short, repeated access to sugar over time leads to prolonged dopamine signaling, greater excitation of the brain’s reward pathways, and a need for even more sugar to activate all of the midbrain dopamine receptors like before. The brain becomes tolerant to sugar, and more is needed to attain the same “sugar high.”
Sugar withdrawal is also real
Although these while these studies were conducted in rodents, it’s not far-fetched to say that the same primitive processes are occurring in the human brain, too. “The cravings never stopped, [but that was] probably psychological,” Andrew told me. “But it got easier after the first week or so.”
Elevated plus maze.
Bd008 (Wikimedia Commons)
Similar withdrawal experiments by others also report depression-like behavior in tasks like the forced swim test. Rats in sugar withdrawal are more likely to show passive behaviors (like floating) than active behaviors (like trying to escape) when placed in water, suggesting feelings of helplessness.
A new study by Mangabeira and colleagues in this month’s Physiology & Behavior reports that sugar withdrawal is also linked to impulsive behavior. Initially, rats were trained to receive water by pushing a lever. After training, the animals returned to their home cages and had access to a sugar solution and water, or just water alone. After 30 days, when rats were again given the opportunity to press a lever for water, those who had become dependent on sugar pressed the lever significantly more times than control animals, suggesting impulsive behavior.
|Typical operant box, with lever.|
Andreas1 (Wikimedia Commons)
Through decades of diet programs and best-selling books, we’ve toyed with the notion of “sugar addiction” for a long time. There are accounts of those in “sugar withdrawal” describing food cravings, which can trigger relapse and impulsive eating. There are also countless articles and books about the boundless energy and new-found happiness in those who have sworn off sugar for good. Despite the ubiquity of sugar in our diets, the notion of sugar addiction is still a rather taboo topic.
Are you still motivated to give up sugar for Lent? You might wonder how long it will take until you’re free of cravings and side-effects, but there’s no answer—everyone is different, and no human studies have been done on this.
After 40 days, it’s clear that Andrew had overcome the worst, likely even reversing some of his altered dopamine signaling. “I remember eating my first sweet and thinking it was too sweet,” he says. “I had to rebuild my tolerance!”
And as regulars of a local bakery in Hershey—I can assure you, readers, that he has done just that.
|Zhing8hong (Wikimedia Commons)|
Originally published at The Conversation.