In the U.S., an estimated 3.2 million adolescents between the ages of 12 and 17 suffer from depression, defined as having at least one major depressive episode in a year. This accounts for 13.3% of adolescents, who experience a period of at least two weeks with a depressed mood, loss of interest in daily activities and other symptoms, such as problems with sleep, appetite, energy, concentration or feelings of self-worth.¹

Depression among adolescents is on the rise, increasing by 30% in the last 10 years.² Many factors may be to blame, but one that continues to fly under the radar is diet, particularly an unhealthy one based on processed foods and fast foods.

Junk Food Diet Linked to Depression in Teens

Researchers at the University of Alabama at Birmingham looked into the role two dietary factors play in symptoms of depression among adolescents, in this case African-American teens who may be at an increased risk of both unhealthy diet and depression.

They analyzed the excretion of sodium and potassium in the urine of 84 urban, low‐income adolescents. Higher levels of sodium in the urine can be an indication of a diet high in sodium, such as processed foods and salty snacks. A low level of potassium, meanwhile, is indicative of a diet lacking in fruits, vegetables and other healthy potassium-rich foods.

As might be expected, higher sodium and lower potassium excretion rates were associated with more frequent symptoms of depression at follow up 1.5 years later. “This study was the first to demonstrate relationships between objective indicators of unhealthy diet and subsequent changes in depressive symptoms in youth,” the study noted.³

It’s possible that eating foods high in sodium and low in potassium may lead to depression by negatively influencing neurotransmitters and neural function during a time that is particularly vulnerable.

“Given the substantial brain development that occurs during adolescence, individuals in this developmental period may be particularly vulnerable to the effects of diet on the neural mechanisms underlying emotion regulation and depression,” the researchers wrote. In addition, poor diet could influence depression by disturbing the gut microbiome, which could further influence brain function.⁴

Past studies have also confirmed the diet-depression link among children and teens. When researchers systematically reviewed 12 studies involving children and adolescents, an association was revealed between unhealthy diet and poorer mental health, as well as between a good-quality diet and better mental health.⁵

The consumption of junk food has also been associated with psychiatric distress and violent behaviors in children and adolescents, which includes worry, depression, confusion, insomnia, anxiety, aggression and worthless feelings, as well as physical fighting, being a victim and bullying.⁶

Unhealthy Diet Linked to Depression in Adults, Too

While teens may be especially vulnerable to the negative effects of a poor diet, adults, too, may suffer mentally from a diet based on unhealthy foods. An inflammatory diet, which can include one high in processed foods, was associated with recurrence of depressive symptoms in women, for starters.⁷

Likewise, in 2018, a systematic review and meta-analysis with a total of 101,950 participants also found an association between a pro-inflammatory diet and risk of depression.⁸ People who ate a pro-inflammatory diet were 1.4 times more likely to suffer from depression.⁹ “Thus, adopting an anti-inflammatory diet may be an effective intervention or preventative means of reducing depression risk and symptoms,” according to the study.¹⁰

Sugar intake, a known inflammatory food, is also specifically linked to common mental disorder and depression. Research published in 2002 also found a “highly significant correlation between sugar consumption and the annual rate of depression.”¹¹

Men consuming more than 67 grams of sugar per day were 23% more likely to develop depression over the course of five years than those whose sugar consumption was less than 39.5 grams per day.¹² Several potential mechanisms were discussed for why a high-sugar diet may influence depression risk, including:¹³

• Sugar may decrease levels of brain derived neurotrophic factor (BDNF), leading to hippocampal atrophy in depression
• Consuming sugar may increase circulating inflammatory markers, which could lead to depressed mood
• A high-sugar diet may cause an exaggerated insulin response, influencing hormone levels and mood
• Sugar has addiction-like effects, which could influence dopamine and mood
• A high-sugar diet may lead to obesity, which could contribute to depression via inflammatory pathways as well as psychosocial factors