The Impact of Sugar and Poor Diet on Teen Mental Health

Featured on US News & World Report. Author: Jamison Monroe Jr.

IT'S A FAMILIAR TROPE: We're feeling blue, so we reach for the ice cream. But research shows that the causality actually runs in the other direction: It's the ice cream that makes us feel blue. In recent years, scientists have linked sugar and sugar additives, as well as fast food and processed food, to depression, addictive behavior and anxiety. In other words, our treats are tricking us.

For example, one long-term study tracked the diets and medical conditions of 8,000 people over 22 years, none of whom was being treated for depression or other mental health disorders at the start of the study. At its conclusion, however, men who consumed 67 grams or more of sugar per day were 23 percent more likely to be diagnosed with depression in a five-year period than men who ate 40 grams or less. On the other end of the demographic spectrum, researchers studied the diet and mental health of 850 girls between the ages of 12 and 18, and found that consumption of fast foods, including ramen noodles, hamburgers, pizza, fried food and other processed foods, was associated with an increased risk of depression.

No matter which way you slice it (or scoop it), the diet–mental health link is a problem for teens, who are already at high risk for depression and anxiety. Add to that the fact that the adolescent brain is more susceptible to advertisements for sweetened drinks, sugary cereal and fast foods, and you have a recipe for disaster. American teens eat more added sugar than any other age group: In fact, one-fifth of a typical American adolescent's calorie intake comes from sugar, according to the Centers for Disease Control and Prevention – mostly from soda, energy drinks and sports drinks.

Rather than a single mechanism by which sugar and poor diet affect mental health, several factors seem to be at play. Here are a few that scientists have zeroed in on.

The gut-brain connection: About 95 percent of serotonin – one of the key hormones involved in mood and emotion regulation – is produced in the gastrointestinal tract, also known as the enteric nervous system. Sometimes called "the second brain" or "belly brain," it consists of some 100 million neurons embedded in the gut walls that carry information to the brain; in fact, 90 percent of the information carried in our primary nerves goes from the gut to the brain, rather than the other way around. As a result, people with healthy and diverse gut microbes are less likely to suffer from anxiety and depression. In fact, studies show that having a healthy gut can reduce social anxiety and lower our reactions to stress.

Sugar and BNDF: According to a study by British researcher Malcolm Peet, the activity of a key growth hormone in the brain called BDNF (brain-derived neurotrophic factor) may be the connecting factor between high sugar consumption and mental health disorders. Regular consumption of sugar triggers a cascade of physiological events that reduce BDNF, and low BDNF levels are linked to depression and schizophrenia, as well as dementia and Alzheimer's.

Sugar's addictive qualities: A growing body of evidence shows that sugar and refined sweetenersact more like addictive drugs than food, creating a high and then a crash. Like drugs (though to a lesser extent), sugar and processed junk food flood the brain with the feel-good chemical dopamine; excess levels of dopamine significantly change the natural functions of the brain over time, impacting mental health. In a 2011 study conducted by Yale University, looking at a milkshake activated the same reward centers of the brain in people with addictive eating habits as are activated in the brains of cocaine users. In another study, rats preferred sugar water to cocaine, even when they were addicted to cocaine prior to the study. And the adolescent brain, which doesn't fully mature until the mid-20s, is particularly vulnerable to addictive stimuli.

Nutritional deficits: When teens fill up on empty calories, they're missing out on the foods that boost mental health. Researchers have identified specific nutrients that support optimal serotonin levels, a balanced microbiome and healthy brain function. But you won't find those nutrients – such as omega-3 fatty acids, magnesium and folate – in processed and sugar-laden foods.

While an emerging methodology known as nutritional psychiatry seeks to draw on these understandings to address depression and other disorders through dietary changes, those of us in the field of adolescent mental health have long understood the significance of "the meal as medicine." That's why any teen treatment program worth its salt (pun not intended) needs to address diet not as an afterthought, but as a central element of healing.

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