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Key points
- Sugar is one of the most common ingredients in the modern U.S. diet.
- The more sugar a person eats, the more sweet-tolerant they become.
- The potent brain effects of sugar help explain the modern sugar obsession and frequent difficulties moderating sugar consumption.
Sugar is the Dr. Jekyll and Mr. Hyde of the nutrition world. Pleasure and poison, desire and danger, love and Lucifer—sugar somehow embodies all these qualities and more in our modern culture.
Part sweet-tasting nutrient (sugar is a source of carbohydrates, one of the three major macronutrients along with fat and protein) and part mind-altering substance, sugar began taking Western civilization by storm in the 18th century. By the 21st century, sugar's candied conquest of the U.S. was complete, appearing as an additive in two-thirds to three-fourths of all food and drinks.1
While most recent media attention to sugar focuses on potential health harms and ways to reduce sugar intake, neuroscientific research about sugar has revealed how and why this plain white substance wields so much power in our lives. Here are five of the most compelling findings:
1. Your sweet tooth may be made (experience and exposure) rather than born (genetic).
In a March 2023 study published in Cell Metabolism,2 researchers reported findings from a clinical trial of normal-weight adults assigned to consume either a daily high-sugar/high-fat snack or a low-sugar/low-fat snack. Over the eight weeks of the study, the researchers observed a pronounced increase in the high-sugar/high-fat group's dopamine response to the sweet snack and a pronounced decrease toward low-sugar/low-fat options.
What does this mean? A sweet tooth can be rapidly learned. With just a few weeks of regular exposure to high-sugar foods, participants' brains in this study rewired themselves to find these foods more pleasurable and dislike alternatives.
2. Sugar tolerance is a real thing.
Have you ever consumed something so sweet that it actually made you feel ill? If so, ask yourself how Americans can stomach eating, on average, over 126 grams (almost 30 teaspoons) of sugar a day.
The answer is that the more sugar we eat, the more sweet-tolerant we become. Many people don't realize that their tastebuds are dynamic. Name any primary taste—sweet, salty, sour, bitter, umami—and consider that the tastebuds detecting them change (i.e., becoming more or less sensitive) depending on how much we're exposed to that taste.
Technically called "chemosensory plasticity," if you wish to impress your friends, numerous studies show in species ranging from insects to humans that high-sugar diets rapidly increase tolerance to sweet tastes.3 What was once too sweet to stomach now becomes just right. For the typical person, this increased sweet tolerance is clearly measurable in just a month.4
3. We love sugar even if we can't taste it.
Mother Nature is too smart to be fooled by artificial sweeteners. She knows how to detect real sugar. In fact, she gave you not one, but two systems to make sure of it. System one is your tastebuds; the ability to detect sweet tastes is programmed right into our mouths.
Most people, however, don't know about the second system. Beyond our conscious awareness, we possess a biochemically mediated pathway connecting our digestive system to the reward circuits in our brain. This reward pathway is more strongly stimulated by sugar than by non-caloric artificial sweeteners.5
This effect is so potent that scientists have conducted studies in insects and rodents where the genes responsible for sweet taste detection are deactivated (i.e., they can no longer taste sweets). The organisms still strongly prefer sugar-sweetened (but not artificially sweetened) water due to this secondary brain-reward system.6
4. Sugar is a pacifier for the mind.
One of the most common reasons fueling our sugar preoccupation is the rapid soothing effect it has on our emotions. Almost from birth in the U.S., we begin pacifying ourselves with food and drink. The most effective "comfort foods" almost always contain significant amounts of natural or added sugars (e.g., pizza is often rated as the favorite comfort food in the U.S., yet even a typical slice of pizza contains five to six grams of added sugar). This is no coincidence.
Sugary foods calm us in two ways: via the hedonic properties of the food (sugar triggering the dopaminergic brain reward pathway) and by altering metabolic and neurohormonal function (e.g., lowering cortisol levels and up-regulating "happiness hormones" like serotonin).7 In combination, these effects make sugar a potent balm for stress and predispose us to overconsumption.
5. Sugar delights the senses but dampens brain function.
Although health experts caution us about sugar consumption due to sugar's contribution to obesity and diabetes, arguably the most worrisome harm associated with sugar is its effect on brain function.
Sugar appears to interfere with healthy brain function in at least two ways. Firstly, some laboratory experiments show that sugar adversely affects genes regulating the hippocampus—an area of the brain critical to memory and learning. Surprisingly, the negative impact of sugar on hippocampal function may be as severe as the effects of early life stressors.8
Secondly, excess sugar consumption causes dysbiotic changes in the gut microbiome (the bacteria living inside the stomach and intestines) that also disrupt the hippocampus.9 Collectively, this research may help explain the growing scientific consensus regarding a potential causal relationship between high-sugar diets and dementia.
Summary
Sugar is a ubiquitous and pleasurable part of modern life. Yet like other two-faced companions of modernity—such as social media and smartphones—we can benefit from research that helps us balance the risks with the rewards.
Facebook image: Drazen Zigic/Shutterstock
References
1. Popkin BM, Hawkes C. Sweetening of the global diet, particularly beverages: patterns, trends, and policy responses. Lancet Diabetes Endocrinol. 2016 Feb;4(2):174-86.
2. Sharmili Edwin Thanarajah, Alexandra G. DiFeliceantonio, Kerstin Albus, Bojana Kuzmanovic, Lionel Rigoux, Sandra Iglesias, Ruth Hanßen, Marc Schlamann, Oliver A. Cornely, Jens C. Brüning, Marc Tittgemeyer, Dana M. Small,
Habitual daily intake of a sweet and fatty snack modulates reward processing in humans,
Cell Metabolism, 2023, ISSN 1550-4131, https://doi.org/10.1016/j.cmet.2023.02.015.
3. May CE, Dus M. Confection Confusion: Interplay Between Diet, Taste, and Nutrition. Trends Endocrinol Metab. 2021 Feb;32(2):95-105. doi: 10.1016/j.tem.2020.11.011.
4. Wise PM, Nattress L, Flammer LJ, Beauchamp GK. Reduced dietary intake of simple sugars alters perceived sweet taste intensity but not perceived pleasantness. Am J Clin Nutr. 2016 Jan;103(1):50-60. doi: 10.3945/ajcn.115.112300.
5. Wilk K, Korytek W, Pelczyńska M, Moszak M, Bogdański P. The Effect of Artificial Sweeteners Use on Sweet Taste Perception and Weight Loss Efficacy: A Review. Nutrients. 2022 Mar 16;14(6):1261. doi: 10.3390/nu14061261.
6. High Dietary Sugar Reshapes Sweet Taste to Promote Feeding Behavior in Drosophila melanogaster. Cell Rep. 2019 May 7;27(6):1675-1685.e7. doi: 10.1016/j.celrep.2019.04.027.
7. Ulrich-Lai YM. Self-medication with sucrose. Curr Opin Behav Sci. 2016 Jun;9:78-83. doi: 10.1016/j.cobeha.2016.02.015.
8. Maniam J, Antoniadis CP, Youngson NA, Sinha JK, Morris MJ. Sugar Consumption Produces Effects Similar to Early Life Stress Exposure on Hippocampal Markers of Neurogenesis and Stress Response. Front Mol Neurosci. 2016 Jan 19;8:86. doi: 10.3389/fnmol.2015.00086.
9. Noble, E.E., Olson, C.A., Davis, E. et al. Gut microbial taxa elevated by dietary sugar disrupt memory function. Transl Psychiatry 11, 194 (2021). https://doi.org/10.1038/s41398-021-01309-7.
