Sugar Cravings: Evolution, Addiction, or Both?

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Illustration by Ryan Brandt

When we think of addiction, our minds automatically jump to alcohol and illicit drugs. However, recent research has called into question whether sugar should be added to this list. There is no question that when given the option, most people choose sugary foods over healthier options, seeking out sweets despite awareness of their adverse health effects – a behavior characteristic of other addictions. This phenomenon interests many scientists, who have sought to understand just what it is about sweets makes them so tempting to the human brain.

A January 2015 study at MIT shed new light on the neurological factors contributing to sugar preference. Focusing on a specific neurocircuit, the LH-VTA loop, which links the part of the brain that controls hunger (the lateral hypothalamus, LH) and a group of neurons central to the brain’s reward circuit (the ventral tegmental area, VTA), researchers genetically modified mice so that the circuit could be turned on and off merely by exposing the mice to different frequencies of light. The mice were then provided with a source of food pellets, as well as a source of sugar. The results of this experiment correlated this neurocircuit with behavior that resembled addiction: when the neurons in the circuit were deactivated, mice chose to eat the pellets and stopped when full. However, when the neurons were activated, mice ate for longer periods of time and would repeatedly travel back to the sugar source, even when they had to cross an electric shocking platform to do so. Although performed with animal models, the experiment could apply to humans because the neurocircuit performs the same functions in the human brain. Therefore, these observations of animal behavior could also demonstrate human sugar addiction.

This research begs the question: what exactly happens in the brain’s reward centers when we consume sugar? As it turns out, the body’s fondness for candy and ice cream comes from multiple chemical responses that follow consumption. Studies by Dr. Yanina Pepino and Dr. Julie Mennella have demonstrated that early in life, sugar can act as an analgesic, essentially a painkiller. This goes away with development. Additionally, it is scientifically established that sugar consumption activates the body’s reward system through dopamine production. As the result of an adaptation to seek out high-energy foods and prevent starvation early in human history, our bodies evolved to respond to sugar consumption with the release of this “feel-good” chemical in the brain. Coincidentally, dopamine is the same chemical responsible for producing a “high” after consumption of illicit drugs.

While this trait once provided an evolutionary leg-up, in today’s society, where candy bars line the checkout counters at grocery stores and soda is often just as readily available as water, this mental hardwiring leads to overconsumption and consequently a range of health problems, from cavities to diabetes. As is the case with drug use, increased sugar consumption causes the body to crave it even more, prompting the brain to require larger amounts of the sugar/drug to reach the same dopamine level again. These chemical changes within the brain resemble those of addiction. This raises the question: are humans addicted to sugar?

Further research has investigated the potential relationships between sugar and addiction. Yanina Pepino, an assistant professor in the division of Geriatrics and Nutritional Science at the Washington University School of Medicine (WUSM) has found that people with family histories of alcohol addiction have increased preference for sweetness. She also mentioned that there are several anecdotal reports in the literature and some studies showing that “when trying to withdraw from drugs and come back from addiction, people many times report having an intense craving for sweetness and feel that increasing their sweet consumption can help keep them from alcohol or heroin.” Although this does not provide evidence that humans experience sugar addiction, it indicates that humans exhibit “addicted-like behavior” towards sugar.

Tamara Hershey, a professor at WUSM who has studied the relationship between dopaminergic abnormalities in the brain and obesity, weighed in on the question of whether or not humans experience sugar addiction. She noted that although we are hardwired to seek out sugar, it is difficult to classify this tendency a true addiction because, unlike drugs, sugar is not a substance one can avoid consuming.

Hershey reflected, “The idea has great heuristic value in that it causes us to think harder about what we mean by ‘food addiction.’ It makes us ask a lot of great questions, but it might not truly be the same as an addiction to a drug.”

Sarah Eisenstein, an Instructor in the Psychiatry Department who worked on the same study, also brought up the difficulty of determining whether overeating or extremely high preference for sugar reflects a deficient or overactive reward system: “Do some people eat more because they need more than other people to feel pleasure, or is it because they are especially sensitive to pleasurable stimuli?” The answer may be different depending on the type of reward and personality of the person in question.

While we may not be able to say humans are “addicted” to sugar, it is widely accepted that sugar elicits chemical responses in the brain just like those present in substance addictions. Every day when we are tempted by caloric options that seem so readily available and decide not to partake, we are fighting our basic human instincts. Somewhat ironically, these instincts are more of a hindrance than a help in today’s society.

 



Lily Sanborn is a sophomore from Bethesda, MD. She can be reached at lsanborn@wustl.edu


'Sugar Cravings: Evolution, Addiction, or Both?' has 1 comment

  1. April 23, 2015 @ 6:18 pm T Denny

    insightful article

    Reply


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