Now playing
01:28
How to eat to live to 100
Brooke Baldwin last show goodbye CNN newsroom vpx_00000217.png
CNN
Brooke Baldwin last show goodbye CNN newsroom vpx_00000217.png
Now playing
03:56
'Get a little uncomfortable': See Brooke Baldwin's last words on air
Now playing
01:24
How Kyra Sedgwick got the cops called on Tom Cruise
Now playing
05:18
Anderson Cooper explains how he overcomes being shy
US Navy
Now playing
01:28
Pentagon confirms UFO video is real, taken by Navy pilot
Kristina Barboza
Now playing
03:09
Grieving mom's advice to other families: You can try to help, support and love
Fancy Feast/Purina
Now playing
01:06
Cat food company makes a cookbook ... for humans
Now playing
02:35
WWII veteran: End of the war was 'the biggest thrill of my life'
Google Earth's new timelapse feature
Google
Google Earth's new timelapse feature
Now playing
01:09
Google Earth's new Timelapse feature shows 40 years of climate change in just seconds
FOX/"The Masked Singer"
Now playing
01:23
'The Masked Singer' reveals identity of The Orca
LONDON, ENGLAND - DECEMBER 07:  A visual representation of the digital Cryptocurrency, Bitcoin on December 07, 2017 in London, England. Cryptocurrencies including Bitcoin, Ethereum, and Lightcoin have seen unprecedented growth in 2017, despite remaining extremely volatile. While digital currencies across the board have divided opinion between financial institutions, and now have a market cap of around 175 Billion USD, the crypto sector coninues to grow, as it continues to see wider mainstreem adoption. The price of one Bitcoin passed 15,000 USD across many exchanges today taking it higher than previous all time highs.  (Photo by Dan Kitwood/Getty Images)
Dan Kitwood/Getty Images
LONDON, ENGLAND - DECEMBER 07: A visual representation of the digital Cryptocurrency, Bitcoin on December 07, 2017 in London, England. Cryptocurrencies including Bitcoin, Ethereum, and Lightcoin have seen unprecedented growth in 2017, despite remaining extremely volatile. While digital currencies across the board have divided opinion between financial institutions, and now have a market cap of around 175 Billion USD, the crypto sector coninues to grow, as it continues to see wider mainstreem adoption. The price of one Bitcoin passed 15,000 USD across many exchanges today taking it higher than previous all time highs. (Photo by Dan Kitwood/Getty Images)
Now playing
03:07
Bitcoin has an energy problem
The new all-electric Mercedes-EQS
Mercedes-Benz AG
The new all-electric Mercedes-EQS
Now playing
01:05
See the new all-electric EQS luxury sedan from Mercedes
Now playing
01:32
Scientists turned spiderwebs into music and it sounds like a nightmare
Jeopardy Productions, Inc.
Now playing
01:02
Aaron Rodgers' Green Bay Packers question stumps 'Jeopardy!' contestants
Now playing
05:18
Coinbase CFO: We're an on-ramp to the crypto economy
CNN
Now playing
02:12
'Too dangerous to do anymore': Sacha Baron Cohen on Borat
(CNN) —  

Preteens are known for their defiant attitudes and dramatic mood swings, but over the last decade a much more disturbing characteristic has been increasing: depression.

A new study finds that one culprit may be a high fast-food, low plant-based diet. When researchers at the University of Alabama at Birmingham analyzed urine from a group of middle schoolers, they found high levels of sodium and low levels of potassium.

“High sodium, you’ve got to think of highly processed food,” said lead author Sylvie Mrug, chair of the psychology department at UAB. “This includes fast food, frozen meals and unhealthy snacks.”

Low potassium, Mrug added, is an indication of a diet that lacks healthy fruits and vegetables that are rich in potassium, such as beans, sweet potatoes, spinach, tomatoes, bananas, oranges, avocados, yogurt and even salmon.

The study also found that higher urine levels of sodium, and potassium at baseline, predicted more signs of depression a year and a half later, even after adjusting for variables such as blood pressure, weight, age and sex.

“The study findings make sense, as potassium-rich foods are healthy foods,” said dietitian Lisa Drayer, a CNN health and nutrition contributor. “So, if adolescents include more potassium-rich foods in their diet, they will likely have more energy and feel better overall – which can lead to a better sense of well-being and improved mental health.”

Disturbing trend

Depression among middle schoolers is on the rise. An analysis of national data found the rate of major depressive episodes among kids 12 to 17 within the last year had increased by a whopping 52% between 2005 and 2017. The rate of depression, psychological distress and suicidal thoughts over the last year among older teens and young adults was even higher: 63%.

Many factors could be contributing to the deadly trend among teens, including a chronic lack of sleep, an overuse of social media, even a fear of climate change.

Prior studies have similarly found a link between fast food, processed baked goods and depression in adults. One study in Spain followed almost 9,000 people over six years and found a 48% higher risk of depression in those who ate more highly processed foods.

A meta-analysis of research from the United States, Spain, France, Australia, Greece and Iran also found a “robust association” between diet and depression. Their results showed people who avoided a highly processed diet and instead followed a Mediterranean diet – fresh fruits, vegetables, nuts, seeds and little red meat or processed foods – had reduced risk of depression.

Small sample, more research needed

The new study was small – only 84 middle school girls and boys, 95% African-American from low-income homes. But the methods were solid: They captured overnight urine samples to objectively test for high sodium and low potassium at baseline and again a year and a half later. Symptoms of depression were gathered on both occasions during interviews with the children and their parents.

But the study could only find an association between sodium and depression, not a cause and effect, and much more research needs to be done, Mrug said.

“It might also be true that a poor diet could be linked to other risk factors for depression, such as social isolation, lack of support, lack of resources and access to healthcare and substance abuse,” Drayer said.

“It might be hard to tease out if diet is the factor or simply a marker for other risk factors for depression.”