Can't stop eating sugar? Don't worry, our love for sugar is written in our genes

Although sugar tastes good, don't be greedy.

By Stephen Wooding, Assistant Professor of Anthropology, University of California, Merced

Compiled by Han Ruobing

Feeling sweet from eating sugar is one of the great pleasures of life. People's heartfelt love for sweets has been "taken" by food manufacturers. Sugar is added to almost all products - yogurt, ketchup, fruit snacks, breakfast cereals, and even so-called healthy foods such as cereal bars, in order to entice consumers to buy.

Children learn in kindergarten that sweets are at the top of the food pyramid, and adults learn from media reports about the role sugar plays in weight gain[1]. There is a huge disconnect between people’s strong attraction to sweets and their rational aversion to them. How did we get into this dilemma?

As an anthropologist who studies the evolution of taste, I believe that a deeper understanding of our evolutionary past can provide important clues as to why we have such a hard time saying “no” to sweet things.

Being able to discern sweetness and get enough food was a fundamental challenge faced by our ancient ancestors.

Basic activities of daily life, such as raising children, finding shelter, and securing adequate food, require energy in the form of calories.[2] Therefore, people who are better at acquiring calories tend to be better at these tasks. They live longer and have more surviving children—from an evolutionary perspective, they are more adaptable.

One of the factors in their success is an advantage in foraging: the ability to detect sweet things, namely sugar, can help.

In nature, sweet tastes signal the presence of sugar, an excellent source of calories, so foragers that can sense sweetness can identify the presence and amount of sugar in potential foods, especially plants.

This ability allowed them to quickly assess calorie content before investing significant effort in collecting, processing, and ingesting those foods, rather than having to grope around blindly. Being able to discern sweetness helped early humans get more calories at a lower cost, thereby increasing their evolutionary success.

The sweet taste gene is crucial to the ability to detect sugar, and evidence for this can be found at the most basic level of biology: your genes. Your ability to sense sweetness is not an accident, but is engraved in your body's genetic blueprint.

This microscopic cross-section of the surface of the tongue. Taste buds are clusters of cells embedded just below the surface of the tongue, facing the mouth through a small hole at the top. The taste buds are the round clusters of cells in the center of the image. Credit: Ed Reschke/Getty Images

The perception of sweetness begins with taste buds[3]. Taste buds are clusters of cells just below the surface of the tongue, exposed to the inside of the mouth through openings called taste pores.

Different subtypes of cells in taste buds respond to specific tastes: sour, salty, umami, bitter, and, of course, sweet. These subtypes produce receptor proteins that correspond to the taste and sense the chemical composition of food as it passes through the mouth.

One subtype produces bitter taste receptor proteins that respond to toxic substances. Another produces umami taste receptor proteins that sense amino acids, the building blocks of proteins. Sweet taste-sensing cells produce a receptor protein called TAS1R2/3, and when the presence of sugar is detected, the cell sends a nerve signal to the brain, which is how you perceive the sweet taste in food.

Genes encode the instructions for how every protein in the body is made. The sugar-sensing receptor protein TAS1R2/3 is encoded by a pair of genes on chromosome 1 of the human genome, TAS1R2 and TAS1R3.

A fruit bat enjoys a sweet treat | Photo credit: Avalon/Getty Images

Compared to other species, sweet taste perception is “destined” for humans. The TAS1R2 and TAS1R3 genes are not unique to humans; they are also found in most other vertebrates, such as monkeys, cows, rodents, dogs, bats, lizards, pandas, fish, and more [4]. These two genes have evolved over hundreds of millions of years and were ready to continue in the first human species.

Geneticists have long known that genes with important functions are preserved intact by natural selection, while genes without important functions tend to decline as species evolve, or even disappear completely. Scientists believe this is the "use it or lose it" theory of evolutionary genetics. The presence of TAS1R1 and TAS2R2 genes in so many species proves the permanence of the survival advantage provided by sweet taste.

The “use it or lose it” theory also explains the remarkable finding that species that do not normally encounter sugar in their diet have lost the ability to sense sweetness.[5] For example, many carnivores carry only fragmented remnants of the TAS1R2 gene.

The human body's sensory system detects all aspects of the environment, from light to heat to smell, but we are not as interested in all of them as we are in the taste of sweetness.

A perfect example is another taste, bitter. In contrast to sweet taste receptors, which detect desirable substances in food, bitter taste receptors detect undesirable substances: toxins. The brain responds appropriately, sweet tells you to keep eating, bitter tells you to spit it out, and this makes sense for evolution.

When your tongue detects a taste, your brain decides how you should react. If specific taste responses are consistently beneficial over generations, natural selection will solidify them[6] and make them instinctual[7].

Just as with bitter taste, newborns do not need to be taught to dislike bitterness – they reject it instinctively. The opposite is true with sugar, which has been shown time and again to be attracted to from the moment we are born.[8] These responses can be shaped by learning, but they are still core components of human behavior.[9]

The baby in the video was given sweet and bitter milk. Scientists have found that even newborns show a strong aversion to bitter tastes. Many parents complain that their two- and three-year-old babies don't like to eat vegetables, and a big reason is that vegetables taste bitter. 丨Video source: Dutch TV VPRO Noorderlicht, 1999 [Please go to the "Fanpu" public account to watch the video]

Since it is human nature to seek out and consume sugar, anyone who decides to cut back on it is fighting against millions of years of evolutionary pressure. People in developed countries now live in an environment where society produces far more sweet, refined sugar than we can eat. The mismatch between our evolutionary drive to consume sugar, our current access to it, and our body’s response to it is destructive. In some ways, we are victims of our evolutionary success.

The appeal of the sweet taste is so strong that it has been described as an addiction, comparable to the difficult-to-break nicotine dependence[10].

But I think it's actually worse. From a physiological perspective, nicotine is an unwelcome foreign substance to our bodies. People crave it simply because it plays tricks on the brain. In contrast, humans' desire for sugar has always existed, genetically encoded for billions of years, because it provides a fundamental survival advantage and is the ultimate "hard currency" on the evolutionary path.

Sugar isn't deceiving you; you're just responding precisely to the program natural selection has set you up to do.

References

[1] Rippe JM, Angelopoulos TJ. Relationship between Added Sugars Consumption and Chronic Disease Risk Factors: Current Understanding. Nutrients. 2016; 8(11):697. https://doi.org/10.3390/nu8110697

[2] O'Connell, James F., Kristen Hawkes. Food Choice and Foraging Sites among the Alyawara. Journal of Anthropological Research 40, no. 4 (1984): 504–35. http://www.jstor.org/stable/3629795.

[3] https://www.scientificamerican.com/article/making-sense-of-taste-2006-09/

[4] Feng, P., Zhao, H. Complex evolutionary history of the vertebrate sweet/umami taste receptor genes. Chin. Sci. Bull. 58, 2198–2204 (2013). https://doi.org/10.1007/s11434-013-5811-5

[5] Jiang, Peihua, et al. Major taste loss in carnivorous mammals. Proceedings of the National Academy of Sciences 109.13 (2012): 4956-4961. https://doi.org/10.1073/pnas.1118360109

[6] Sheehan, Michael J., et al. Behavioral evolution: can you dig it? Current Biology 28.1 (2018): R19-R21. https://doi.org/10.1016/j.cub.2017.11.016;

[7] DARWIN, C. Origin of Certain Instincts. Nature 7, 417–418 (1873). https://doi.org/10.1038/007417a0

[8] Ventura, Alison K., and Julie A. Mennella. Innate and learned preferences for sweet taste during childhood. Current Opinion in Clinical Nutrition & Metabolic Care 14.4 (2011): 379-384. https://doi.org/10.1097/MCO.0b013e328346df65

[9] https://www.npr.org/sections/thesalt/2014/03/19/291406696/why-a-sweet-tooth-may-have-been-an-evolutionary-advantage-for-kids

[10] Wiss, David A., Nicole Avena, and Pedro Rada. Sugar addiction: from evolution to revolution. Frontiers in psychiatry 9 (2018): 545. https://doi.org/10.3389/fpsyt.2018.00545

This article is translated from Stephen Wooding, A taste for sweet – an anthropologist explains the evolutionary origins of why you're programmed to love sugar

Original link: https://theconversation.com/a-taste-for-sweet-an-anthropologist-explains-the-evolutionary-origins-of-why-youre-programmed-to-love-sugar-173197

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