Have you ever wondered why only hummingbirds drink nectar from bird feeders?
Unlike sparrows, finches and most other birds, hummingbirds can relish sweetness because they carry the genetic instructions needed to detect sugar molecules.
Like hummingbirds, we humans can sense sugar because our DNA contains gene sequences that code for the molecular detectors that allow us to detect sweetness.
But it’s more complex than that. Our ability to perceive sweetness, as well as other flavors, involves a delicate dance between our genetic makeup and the foods we encounter from womb to table.
Neuroscientists like me are working to decipher how this intricate interplay between genes and diet shapes taste.
In my lab at the University of Michigan, we’re diving deep into one specific aspect, which is how consuming too much sugar dulls the sense of sweetness. Taste is so central to our eating habits that understanding how genes and the environment shape it has crucial implications for nutrition, food science and disease prevention.
The role of genes in perceiving taste
As with hummingbirds, the human ability to discern the taste of food depends on the presence of taste receptors. These molecular detectors are found on sensory cells, which are housed within the taste buds, the sensory organs on the surface of the tongue.
The interactions between taste receptors and food molecules give rise to the five fundamental taste qualities: sweetness, savouriness, bitterness, saltiness and acidity, which are transmitted from the mouth to the brain via specific nerves.
Julia Kuhl and Monica DusCC BY-NC-ND
For example, when sugar binds to the sweet receptor, it signals sweetness. Our innate preference for the taste of some foods over others is rooted in how the tongue and brain have become wired throughout our evolutionary history. Taste qualities that signal the presence of essential nutrients and energy, such as salt and sugar, send information to pleasure-related areas of the brain. Conversely, tastes that warn us of potentially harmful substances, such as the bitterness of certain toxins, are linked to those that make us feel discomfort or pain.
While the presence of genes coding for functional taste receptors in our DNA allows us to detect food molecules, how we respond to them also depends on the unique combination of taste genes we carry. Like ice cream, genes, including those for taste receptors, come in different flavors.
Take, for example, a taste receptor for bitterness called TAS2R38. Scientists have found small changes in the genetic code of the TAS2R38 gene between different people. These genetic variants influence how people perceive the bitterness of vegetables, berries and wine.
Follow-up studies have suggested a link between those same variants and dietary choice, particularly regarding consumption of vegetables and alcohol.
There are many other variations in our genetic repertoire, including those for the sweet taste receptor. However, whether and how these genetic differences affect our taste and eating habits is still being worked out. What is certain is that while genetics lay the foundations for sensations and taste preferences, experiences with food can profoundly reshape them.
How diet affects taste
Many of our innate sensations and preferences are shaped by our early experiences with food, sometimes before we’re even born. Some molecules from the mother’s diet, such as garlic or carrots, reach the taste buds of the developing fetus through the amniotic fluid and can influence the appreciation of these foods after birth.
Infant formula can also affect food preferences later on. For example, research shows that infants fed non-cow’s milk formulas, which are more bitter and acidic due to their amino acid content, are more accepting of bitter, acidic and salty foods such as vegetables after weaning than who consume cow’s milk based formula. And children who drink sugar water strongly prefer sweet drinks as early as age 2.
The effect of food on our gustatory predispositions doesn’t stop in early childhood: What we eat as adults, especially our sugar and salt intake, can also shape how we perceive and potentially choose food. Reducing sodium in our diet decreases our preferred level of saltiness, while consuming more makes us appreciate saltier foods.
Something similar happens with sugar: Reduce sugar in your diet and you may find food sweeter. Conversely, as research in rats and flies suggests, high levels of sugar can dull the sensation of sweetness.
While we researchers are still working out exactly how and why, studies show that high sugar and fat intakes in animal models dampen the responsiveness of taste cells and nerves to sugars, change the number of available taste cells, and even reverse the Genetic switches in cell DNA taste.
In my lab, we have shown that these taste changes in rats return to normal within a few weeks when the extra sugar is removed from the diet.
The disease can also affect taste
Genetics and food aren’t the only factors that influence taste.
As many of us discovered during the height of the COVID-19 pandemic, illness can play a role too. After testing positive for COVID-19, I couldn’t tell the difference between sweet, bitter, and sour foods for months.
Researchers have found that around 40% of people infected with SARS-CoV-2 have impaired taste and smell. In about 5% of these people, these taste deficits persist for months to years.
While researchers don’t understand what causes these sensory alterations, the leading hypothesis is that the virus infects cells that support taste and smell receptors.
Train your taste buds for healthier eating
By shaping our eating habits, the intricate dance between genes, diet, disease and taste may influence the risk of chronic disease.
In addition to distinguishing food from toxins, the brain uses taste signals as a proxy to estimate the satiating power of foods. In nature, a food’s stronger taste in terms of sweetness or saltiness is directly related to its nutrient levels and calorie content. For example, one mango contains five times the amount of sugar as one cup of strawberries, which is why it tastes sweeter and is more filling. Therefore, taste is important not only for enjoyment and choice of food, but also for regulating food intake.
When taste is altered by diet or disease, sensory and nutritional information may become “decoupled” and no longer provide accurate information to our brain about portion size. Research shows that this can also occur with the consumption of artificial sweeteners.
And indeed, in recent studies in invertebrate animal models, our lab found that changes in taste caused by high dietary sugar intake led to higher nutrition by compromising these dietary predictions. In particular, many of the meals
brain patterns and changes we observed in flies were also discovered in people who ate foods high in sugar or fat or who had a high body mass index. This raises the question of whether these effects also result from taste and sensory alterations in our brains.
But there is an upside to the adaptable nature of taste. Because diet shapes our senses, we can actually train our taste buds and brain to respond to and prefer foods with lower amounts of sugar and salt.
Interestingly, many people already report that they find foods excessively sweet, which may come as no surprise since between 60% and 70% of grocery store foods contain added sugar. Reformulating foods tailored to our genes and the plasticity of our taste buds could be a powerful and practical tool for improving nutrition, promoting health, and reducing the burden of chronic disease.
Monica Dus, associate professor of molecular, cellular and developmental biology, University of Michigan
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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