Historically, the term “addictive” was associated with illegal substances that produce a high intensity of intoxication and induce severe withdrawal symptoms. However, there has been a shift in our understanding of what constitutes an addictive substance. For example, nicotine became recognized as an addictive substance without fitting into the traditional criteria: one is not under the influence while smoking, withdrawal does not require hospitalization and smoking is legal in most instances. Since then, the concept of addiction has evolved, with a new focus on a person’s inability to abstain from a given substance and continuing consumption despite negative consequences.
Emerging evidence suggests that addiction to sugar is beginning to surface in the Western world, with some even saying that this dependence can be explained within the same neurobiological framework as drug addiction. But is “addiction” really an appropriate concept to apply to sugar consumption? First, let us consider a basic view of how drug addiction works. Most drugs of abuse are non-nutritive substances that physically interact with molecules on brain cells to induce a gratifying feeling. Sugar works similarly in the sense that it also activates the pleasure centre circuitry in the brain. However, there are many differences in how drugs and sugar affect our body, particularly in the potency of the intensity, frequency and duration of sugar versus drug cravings.
Generally speaking, there are two components to how sugar affects our body. First, there is the taste component that activates the areas of the brain associated with dopamine reward-motivation circuitry. In fact, the amount of dopamine released due to sugar ingestion is proportional to the self-reported level of pleasure gained by consuming the food containing sugar. Second, naturally occurring sugars exert a caloric feedback to the hypothalamus, a region of the brain that regulates food intake in the context of energy and nutritional needs. Supporting evidence can be found in rodent models where scientists have observed that extracellular glucose levels cause neurons in the hypothalamus to fire irrespective of gustatory input.
But not all sugars are nutritional, making some of them more similar to drugs, as the reward circuitry is engaged in response to consumption, but ingestion is not regulated in response to caloric intake. In particular, artificial sugar often lacks the nutritional components found in naturally occurring sugar. For instance, natural fructose found in fruits is accompanied by an intake of potassium, antioxidants, high fibre and vitamin C. However, fructose that is added artificially – typically found in sweeteners – is stripped of these beneficial components, despite it still being fructose. Moreover, there is a stark difference in the quantity of fructose naturally found in fruit versus the amounts that are added artificially to drinks and food. While fructose makes up about 1% of a peach’s weight, in some artificially sweetened drinks, fructose accounts for half of the beverage’s weight.
Studies have shown that rodents have a preference for natural sugar with caloric benefit over sucralose (an artificial, non-nutritive sweetener). When scientists coupled the animal’s consumption of sucralose with optogenetic stimulation of their neurons, their brain was tricked into thinking that they are receiving caloric energy despite sucralose having none. This stimulation even led to an eventual preference of sucralose over natural sugar, perhaps because overly stimulating their brain may have caused them to think there are more calories in sucralose than in natural sugar. Similarly, scientists have also observed using functional magnetic imaging in non-obese men that while natural sugar ingestion leads to a prolonged signal depression in the hypothalamus that regulates food intake, the same cannot be observed with sucralose ingestion. In summary, when sweetness is decoupled from caloric content (as is the case for artificial sugar), it only partially activates the food reward pathways. This lack of satisfaction in the caloric content, in turn, fuels food-seeking behaviour or increases the risk of sugar addiction.
The difference in the manufacturing process of artificial sugars partially explains why artificial sugar behaves differently than natural sugar in the body. Interestingly, the extraction processes involved in the making of artificial sugar and drug production are very similar. Once sugar cane is crushed and boiled down to a syrup before being stripped of its vitamins and minerals to become what we know as the pure white sugar crystals, it is now endowed with greater potency and efficiency in entering our system. Similarly, coca leaf, when chewed or steeped as a tea, provides stimulating effects comparable to that of a cup of coffee without a huge risk for addiction. However, similar to artificial sugar production, coca leaf can be crystallized to become cocaine. The same can be applied to other drugs such as poppy seeds to opium. So, it is really the processing of natural products and artificially creating concentrated versions of the substances that make them addictive and harmful to our body.
If sugar addiction is a real phenomenon, then what are its health implications? Because most artificial sugars are either sucrose (table sugar, composed of glucose and fructose) or high fructose corn syrup (also composed of glucose and fructose), a cross-sectional study looked at oral ingestion of these two sugars and their effect on lean and obese adolescents. Using functional MRI, researchers were able to show that glucose or fructose increased perfusion of the prefrontal cortex, an area important for executive function, in lean individuals. However, the same sugars led to reduced perfusion of the prefrontal cortex and a simultaneous increased activity in the reward-motivation and pleasure centres of the brain in obese individuals. This finding suggests that obese adolescents may lack the ability to control intake of foods containing artificial sugar such as sugar-sweetened beverages due to an increase in perceived pleasure. However, as is the nature of cross-sectional studies, the unanswered question is: did obesity or the changes in the brain response come first?
Although there are few studies that have specifically examined sugar addiction in humans, and it is tricky to translate animal data to humans as we rarely consume sugar in isolation, many have called for changes in policy and regulation. For instance, in 2015, the World Health Organization recommended reducing artificial sugar intake to less than 5% of daily caloric content as a means to reduce the risk of obesity. Furthermore, the American Academy of Pediatrics recommended parents to not feed infants fruit juice due to its high sugar content. But the political and legal implications are far more complex, and the trifecta of public health officials, food industry and consumers has different views on sugar regulation. From the public health officials’ stance, emerging evidence supporting a link between obesity and sugary beverages is strong enough to push for stricter control of labels, advertisements and higher taxation. Conversely, the food industry contends that obesity is a complicated issue and focusing on sugar alone would have no effect on obesity rates. Ultimately, consumers demand the right to receive information about the food they eat, although to what degree this information can be used effectively by the general population is also often called into question.
Artificial sugar consumption is certainly rising in the Western world. In the United States alone, more than 6,000 new products containing artificial sugar were launched between 1999 and 2004, and these products range from carbonated drinks to baby food. In 2008, Consumer Report from a market research firm also stated that 65% of American households purchased at least one sucralose-containing product, one of the many artificial sugars available to us today. While initially, artificial sugar made its way to the market for people choosing the sweet flavour without the caloric content, several large-scale prospective cohort studies have shown that there is actually a positive correlation between artificial sugar consumption and weight gain. With this in mind, it is important to ask whether it is worth the risk of addiction. Or perhaps, more importantly, is it already too late to avoid artificial sugar even if we do decide it is not worth the risk?
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