A Bittersweet Truth: The Neuroscience of Sugar and Addiction



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 blood-sugar 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.

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