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Sugar May Be Stealing Your Happiness

Sugar isn’t just a cause of metabolic disease. Mental health is another casualty

Key points

  • Most people consider sugar risks as limited to physical health problems such as obesity or tooth decay.
  • Sugar intake is increasingly linked to poor mental health.
  • Sugar shows addictive properties, causes unhealthy microbiome changes, and may harm brain function.

According to legend, vampires could not enter a home until invited. Only then could they prey on their victims. Knowledgeable of this barrier, vampires skillfully concealed their intentions, mastering the arts of guile and seduction in ways that have made them the subject of both fear and fascination (see the “Twilight Saga” for a romantic Hollywood incarnation). Although scientists are still searching for their first confirmed vampire, they have discovered an even more seductive villain that we have unwittingly welcomed to our homes and schools: sugar.

Thanks to researchers such as Dr. Laura Schmidt and journalists such as Michael Moss, we now know that the sugar industry engaged in decades of deceptive marketing, research manipulation, and even outright bribery to portray sugar as a harmless source of pleasure (1). Contrary to this industry-manufactured image, however, a fast-growing mountain of metabolic research shows that sugar is a dietary wolf in sheep's clothing. This research directly implicates sugar in the development of heart disease, diabetes, obesity, fatty liver disease, high cholesterol and hypertension, and potentially even cancer and dementia (Dr. Lustig’s “Sugar: The Bitter Truth” on YouTube for an introduction to this research).

After years of false starts, the tide may finally be beginning to turn. Nutrition guidelines from the federal government and influential organizations such as the American Diabetes Association are lowering their recommended intake of sugar. More than two dozen countries have instituted sugar taxes in an attempt to recoup the staggering healthcare costs associated with metabolic diseases. And sales of sugar-containing beverages and foods in the U.S. have even shown modest declines. Make no mistake, however, battles for public health are fought over decades, not months or even years. In the meantime, it is primarily up to us as individuals, families, school systems, and communities to make changes that can improve our health and quality of life.

Although most of the research attention given to sugar in recent years centers on its metabolic disease effects, there is also now a large scientific literature demonstrating adverse sugar effects on mental health. This is counterintuitive to many. Sugar may seem like an obvious contributor to negative health effects such as tooth decay and weight gain, for instance, yet we stereotypically associate sugar with positive emotional effects from sources such as desserts, birthday parties, and holidays. Similarly, many people turn specifically to sugary foods to lift their negative moods and manage stress. How can these widespread celebratory practices and intimate comfort food experiences with sugar be wrong?

Neuroscience explains how sugar can simultaneously make us happy and unhappy. At the neurochemical level, sugar induces short-term feelings of reward and desire by increasing the action of an important neurotransmitter called dopamine. Dopamine has many effects, among them the ability to induce temporary increases in pleasure chemicals such as endorphins and endocannabinoids. This means that our personal associations of improved mood and stress relief when eating sugary foods are real but fleeting.

At the same time, when the occasional dessert becomes a regular diet of added sugars (more than 75 percent of foods in a typical grocery store now contain added sugars), two happiness-stealing chemical consequences emerge: 1) the transient dopamine activity is followed by hormone responses that perpetuate cravings and negative emotions over time; and 2) the more we rely on dopamine to feel good and escape feeling bad, the less we are able to produce serotonin. Because serotonin is the neurotransmitter responsible for feelings of contentment, confidence, and satisfaction (e.g., antidepressants and psychedelics both increase serotonin activity in the brain, for example), this is a disastrous tradeoff.

Recent laboratory and neuroscience research suggests relationships between high sugar intake and each of the following mental health outcomes:

1. Cravings, addiction. The idea that sugar is addictive remains controversial among experts. Controlled research, however, demonstrates unequivocally that sugar has addictive properties: it activates dopamine reward pathways in ways similar to addictive drugs such as cocaine; high sugar intake causes downregulation of dopamine receptors that we call “tolerance” among users of addictive drugs; a high sugar diet causes cravings and withdrawal symptoms for many users; and sugar often leads to overconsumption (e.g., binge eating) that is difficult for the person to control despite adverse consequences.

2. Tooth decay and dementia. There is growing evidence that excess sugar consumption can contribute to forms of dementia such as Alzheimer’s Disease. What was once only a suspect cross-sectional relationship between higher reported levels of sugar intake among patients with dementia is now a connection supported by careful laboratory studies indicating the biological pathways through which a high sugar diet can directly harm the brain. One of the most important pathways involves sugar effects on tooth decay. Among the many negative effects on oral health, sugar contributes to gingivitis. While any dentist will tell you that gingivitis is a serious health condition by itself, its even more sinister effects on the brain were only recently discovered by studies showing that gingivitis bacteria can cross the blood-brain barrier and contribute to brain proteins associated with Alzheimer’s Disease.

3. Microbiome changes. The microbiome in our gut is linked to a growing number of psychiatric conditions: anxiety and depression, ADHD and autism, and dementia, among others (2). Although we remain years away from knowing the optimal types and combinations of microorganisms to populate in our stomach and intestines to promote good health, sugar appears to have at least two negative effects: it decreases bacterial diversity (similar to reducing forms of life in a rain forest that could cause entire food chains to collapse); sugar promotes microorganisms associated with increased inflammation (amongst other harms, higher levels of inflammation may cause depressive symptoms). Some microbiome research suggests that a high sugar diet can become self-reinforcing through the changes it causes to our gut composition that increase our preferences for high sugar foods.

4. Leptin and emotions. One of the most important but little-discussed ways that a high sugar diet causes negative emotions is through changes in hormones. Most people know that sugar increases levels of a hormone called insulin. Insulin is a hormone with powerful anabolic properties (e.g., insulin is used by some muscle-building athletes) and plays an important role in appetite and body fat. Insulin also works with other appetite hormones such as leptin. Leptin is created in fat cells and provides information to the brain about energy availability. In a lean child or adult, the brain is very sensitive to leptin. When leptin levels rise, this signals satiety to the brain and increases energy expenditure. High levels of insulin, however, such as in people with metabolic disorders or eating high sugar diets, decrease brain sensitivity to leptin. This is called leptin resistance. This means that the brain detects low levels of leptin even leptin levels are in fact high. When leptin levels are low (e.g., a person on a crash diet) or we become leptin resistant, negative emotions are one of the common symptoms. Studies tracking leptin levels and emotions in real-time, for example, report correlations as high as .70 between low leptin/leptin resistance and negative emotions such as anxiety and sadness. A correlation of .70 is a very large effect in statistical terms.

5. Replacing happiness with pleasure. Imagine that pleasure (dopamine) and satisfaction (serotonin) sit on a happiness seesaw in your brain. Among people with higher levels of life satisfaction, their lifestyle and neurochemistry are usually skewed to the right; a lot of quality interpersonal connection, rewarding forms of contribution, and meaningful work, play, and community roles are “balanced” with occasional simple pleasures. For modern Americans, however, the skew is more often to the left; lifestyles consisting of lots of simple pleasures and very little of the stuff that creates gratitude, joy, or contentment. While most simple pleasures – smoking, drugs, gambling, alcohol – are regulated due to their established dangers, sugar is a pleasure source that remains cheap and convenient. And not only is sugar legal, but it has also been actively promoted for decades by government food subsidies and nutrition guidelines. The easy access and ubiquitous availability explain how sugar can cause so much harm to our physical and mental health.

Fortunately, we don’t need to divorce sugar from our lives to make meaningful improvements to our well-being. It does mean, however, that if we want to feel and function at our best that sugar needs to make up a smaller part of our diet. For example, updated guidelines from the American Heart Association and World Health Organization recommend no more than 100 calories of sugar a day for women (that’s 6 teaspoons or 24 grams if you’re reading labels) and 150 calories of sugar for men (9 teaspoons or 36 grams). This is the upper recommended sugar intake for those above age 2. For infants, the upper recommended limit of sugar is zero. For reference sake, the typical American consumes two to three times more sugar than these recommended amounts.

For those accustomed to a high sugar diet, making reductions of this magnitude are unlikely to be an overnight shift and more likely to result from gradual steps to reduce food and drink sources containing the highest amounts of added sugars. Knowing more about this emerging link between excess sugar and poor mental health may be a critical source of motivation in this process.


JAMA Intern Med. 2016;176(11):1680-1685. doi:10.1001/jamainternmed.2016.5394

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