Sugar: 5 Surprising New Findings From Neuroscience

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.

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,” numerous studies show in species ranging from insects to humans that high-sugar diets rapidly increase tolerance to sweet tastes. 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.

Mother Nature is too smart to be fooled by artificial sweeteners. She knows how to detect real sugar. In fact, she gave us not one, but two systems to make sure of it. System one is our 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.

This effect is so potent, for example, that scientists can conduct studies in insects and rodents where the genes responsible for sweet taste detection are deactivated (i.e., they can no longer taste sweets) and the organisms still strongly prefer sugar-sweetened (but not artificially sweetened) water due to this secondary brain-reward system.

One of the most common reasons fueling our sugar preoccupation is the rapid soothing effect it has on our emotions. Almost from birth, 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). In combination, these effects make sugar a potent balm for stress and predispose us to overconsumption.

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.

Secondly, excess sugar consumption causes dysbiotic changes in the gut microbiome (the bacteria living inside the stomach and intestines) that also disrupt the hippocampus. Collectively, this research may help explain the growing scientific consensus regarding a potential causal relationship between high-sugar diets and dementia.

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 versus rewards.