A Bittersweet Truth: The Neuroscience of Sugar and Addiction

(Editor’s note: This article from the Spring 2016 issue of Brain World magazineIf you enjoy this article, consider a print or digital subscription!)

Let me preface by saying that generally, I’m a pretty healthy person. In fact, I’m probably more health conscious than most — I limit my caffeine intake, I eat plenty of leafy greens, lean protein, and healthy fats. I have a couple glasses of red wine a week — for the flavonoids, obviously — and I can’t remember the last time I ate fast food.

But as I sit here, researching content on how certain foods affect the brain, I have a Starbucks green tea latte to my right and a bag of sour Jelly Belly candies to my left — a bag that I can’t stop reaching for. I’ve already eaten more than I told myself I would, and at the rate I’m going, I’ll have only the lemon-flavored ones left by the time I finish writing this piece.

I know that too much sugar is bad for the waistline. I know that it can affect heart health, cause blood-sugar spikes, crashes, and offers basically zero nutritional value. There was also a recent study showing that sugar, possibly more so than salt, can lead to fatty liver disease, hypertension, Type 2 diabetes, obesity, increased cancer risks, and kidney disease. Yikes! There’s now increasing evidence that high levels of sugar consumption can have damaging effects on brain health, from cognitive function to your general psychological well-being.

A study out of University of California, Los Angeles, discovered that high levels of sugar were shown to slow down the brain by damaging synaptic activity, resulting in an obstruction to learning and memory. Since synaptic activity is the way brain cells communicate with each other and send information, damage to these pathways and slower synapses means information isn’t getting where it’s supposed to as quickly. Think of information traveling like a car on an LA freeway at midnight versus that same freeway at rush hour.

The study’s lead author, Dr. Fernando Gomez-Pinilla, also explained that heavy sugar intake caused the rats from the study to develop a resistance to insulin — a hormone that controls blood-sugar levels and also regulates how brain cells function. Insulin helps your brain better communicate by strengthening the synaptic connections between brain cells, and in turn, assists in the formation of stronger memories. So, when insulin levels in the brain plummet after too much sugar consumption, cognition and thinking can get foggy. As if that’s not enough, there was another research study to offer mounting evidence that high blood sugar increases your risk for developing neurodegenerative disorders like Alzheimer’s.

Here’s the thing. Even though many Americans know the negative health effects of sugar, our consumption over the years hasn’t subsided. We’re simply eating too much of it. It’s everywhere — it takes over celebrations, it utterly dominates the holidays, and it’s in all kinds of packaged foods, drinks, and even, Alcoholics Anonymous meetings. (On a side note: AA’s 12 Step bible suggests keeping candies on hand to replace drug and alcohol cravings. We’ll talk shortly why this is possibly the worst idea ever for recovering addicts.) There’s something about this sweet substance that’s irresistible. Addictive. We’re a nation hooked on sugar.

Dr. David Ludwig, director of the New Balance Foundation Obesity Center at Boston Children’s Hospital, performed a study that took MRI brain scans of 12 obese men after finishing off two milkshakes. Both milkshakes had the same amount of calories, protein, fat, and carbohydrates, and they both tasted equally sweet. The difference, however, was that one milkshake had a much higher glycemic index from the carbohydrates compared to the other.

After the men consumed the milkshake with the higher glycemic index, their bloodsugar levels spiked as expected, and, unsurprisingly, crashed a few hours later, leaving them hungry and wanting more. However, Ludwig pointed out brain scans revealing that the higher sugar milkshake activated the nucleus accumbens — a central player in the brain’s reward circuit that’s operated by two essential neurotransmitters: dopamine, the feel-good hormone known for promoting desire; and serotonin, which affects mood, feelings of well-being, and inhibitions. It’s also the same part of the brain that addictive drugs and behaviors like gambling trigger.

Here’s what happens: you eat sugar; the sugar sends signals to certain parts of the brain and activates the reward pathways, causing a surge of dopamine and serotonin. It also causes your prefrontal cortex — the head honcho of the brain — to release hormones that nag you to remember the experience you’re having in order to make it happen more often. During the sugar crash, there’s a dopamine and serotonin deficit, causing feelings of moodiness and even depression. You get “hangry.” These reactions are not unlike those induced by addictive opioids and nicotine. In short, sugar hijacks the brain’s reward pathway, explains neuroscientist Jordan Gaines Lewis. When the reward system is activated too much and too often, it throws our equilibrium off balance.

Check this out: For AA groups, sugar was (and maybe still is) considered a viable replacement for drugs and alcohol. Recovering addicts were instructed to keep candies or snacks on hand for when a drug or alcohol craving would surface. While it may have helped distract these people from their drug cravings, it also gave way to a new addiction that spiked the same parts of the brain their drugs once did. As such, the cycle began anew — according to Dr. Pamela Peeke, author of “The Hunger Fix” and professor at the University of Maryland: “Once off the drugs, the brain craves the uber rewards of the hyperpalatables — Mint Milanos, Oreos, any sugar. An apple’s reward doesn’t cut it. So you end up with the transfer addiction. It’s off the cocaine, onto the cupcakes.”

It’s this constant merry-go-round of sugar cravings, highs, and crashes that contributes to the vicious cycle of so many eating disorders, from binge eating to bulimia. Sugar offsets the normal appetite system and creates a feeling of satiety that’s just out of reach. Notice how you never get full off one cupcake? This is the root of why binge eaters and bulimics will typically binge on sugar and carbohydrates. For a short moment after binging, there’s a high from the surge of dopamine. In turn, when this subsides, they’re left wanting more.

Taking things a step further, the brain’s reward systems rely on the neurotransmitter dopamine for activation. In both drug addictions and obesity, there’s a decrease in the number of dopamine D2 receptors. This reduction is associated with diminished enjoyment of food or drugs. In the same account, decline of dopamine D2 affects areas of the brain that support self-control, leading to a weaker ability to resist temptation. Dr. Nicole — a faculty member at the New York Obesity Research Center at Columbia University, and expert in the field of food addiction — explains: “People can have all the willpower in the world. But if the brain reward system is being activated in a way that causes them to have a battle against their willpower, then it can be very difficult for them to control their intake.”

We aren’t born loving cookies and hating broccoli. It’s a conditioning that gradually happens over time in response to the things we repeatedly eat. So, if it is indeed we ourselves who condition our cravings, then it may be possible to reorient them from cake to carrots. Underwhelming, yes, but it could mean a longer lifespan and lower risk of neurodegenerative diseases.

In fact, there was a study from Tufts University that looked at the brain scans of a group of people before assigning half of them to a behavioral intervention program geared toward weight loss and healthy eating. The program taught lessons on portion control and created menu plans geared around specific dietary targets. Six months later, a second round of brain scans showed the part of the brain associated with addiction and learning had changed in people who participated in the program. For the control group that didn’t participate, there was no change. But for the others, their brain scans reflected a more active sensitivity to healthier foods, with decreased sensitivity to less healthy alternatives. In other words, these participants increased their brain’s desire for healthier stuff and decreased their preference for junk.

So, yes. It is possible that I could recondition myself to avoid this bag of candy next to me. And given what it’s probably doing to my brain, it’d be better for me to reach for a piece of gum instead. But it doesn’t stop here. They key is to retrain the brain to start eating fewer foods with sugar and high-glycemic loads (think processed carbs — white bread, white potatoes, etc.). By keeping surges of blood sugar low, this could in turn modulate the activity of the brain’s reward system and lessen cravings overall.

We live in a society where there’s temptation at every turn: cupcakes at birthdays, chocolate on Valentine’s, desserts at every holiday. There’s no getting around it. But the good news is that adopting a healthier lifestyle can get easier over time. Awareness becomes behaviors, new behaviors morph into habits, and what was once a craving will become merely a passing thought.

Pretty sweet, no?

(Editor’s note: This article from the Spring 2016 issue of Brain World magazineIf you enjoy this article, consider a print or digital subscription!)



  1. Kudos to you! Nothing more left to explain the effects of sugar on the brain.

    Before taking any steps against sugar we should first ask ourselves are we cutting down natural sugars or the refined sugars. Because, Sugar in the form of Glucose is one of the primary sources of energy.

    According to a survey, Americans have 20 teaspoons of Sugar per day. Whereas the recommended sugar intake per day given by American Heart Association is 9 teaspoons for men, 6 teaspoons for women and 3-6 teaspoons for children.

    I have cut down added sugar to few teaspoons per day now. Awaiting the results!

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