Raw fruits and vegetables may be better for your mental health than cooked ones, according to a new study from the University of Otago in New Zealand. The study, published in Frontiers in Psychology, found that people who ate more uncooked produce had lower levels of symptoms related to depression and other mental illnesses, compared to those who ate more cooked, canned, or processed varieties.
The study was only able to show an association between raw produce and better mental health, not a cause-and-effect relationship. But the researchers say the link could have to do with the fact that many fruits and vegetables have more nutrients in their natural state—and that those nutrients may have a positive impact on mood and brain chemistry.
For the study, researchers surveyed more than 400 young adults, ages 18 to 25, in the United States and New Zealand. People in this age group tend to consume a relatively low level of fruits and vegetables, the authors point out, and are also at high risk for mental health disorders.
The participants were asked about their typical consumption of fruits and vegetables, including which specific varieties they ate and how the produce was prepared. They were also screened for symptoms of mental illnesses, like depression and anxiety.
The study authors knew that plenty of other variables could influence both mental health and fruit and vegetable consumption. So they also made sure to consider participants’ exercise habits, overall diet, existing health conditions, socioeconomic status, ethnicity, and gender.
Even after controlling for those lifestyle and demographic factors, the association between raw vegetables and positive mental health outcomes was significant. Raw fruit and vegetable consumption predicted lower levels of depression and improved levels of psychological well-being, the authors wrote, including positive mood, life satisfaction, and flourishing.
By contrast, intake of fruit and vegetables that were processed (by cooking, canning, or other methods) was associated only with positive mood—not with any of the other mental health variables measured in the study.
Overall, the 10 foods in the study that were most strongly associated with positive mental-health outcomes were carrots, bananas, apples, dark leafy greens (such as spinach), grapefruit, lettuce, citrus fruits, fresh berries, cucumber, and kiwifruit.
In the raw vegetable category, celery, cabbage, red onion, tomato, and mushrooms were also associated with positive mood. The authors note that these veggies can be considered “salad fixings,” and they cite previous research linking salad consumption with lower stress levels. In the processed produce category, pumpkin, mixed frozen vegetables, potatoes and sweet potatoes, broccoli, and eggplant were linked to positive mood, as well.
The researchers say their findings are important because most current health guidelines do not distinguish between raw and cooked or canned fruits and vegetables. “If our patterns are confirmed in intervention studies, it would suggest that heath policies could focus on promoting the consumption of raw and unprocessed produce for optimal well-being,” they wrote in their paper.
The study wasn’t designed to answer the question of why raw foods might be better for mood and mental health, and the researchers can only speculate. But they say that nutritional differences between raw and cooked produce may play a role.
“Raw fruits and vegetables may provide greater levels of micronutrients than processed fruits and vegetables, which could explain their stronger association with improved mental well-being,” they wrote. For compounds like vitamin C and carotenoids that have been linked to mental health, “cooking and canning would most likely lead to a degradation in nutrients, thereby limiting their beneficial impact on mental health.”
However, the study authors point out, this level of degradation varies from food to food—and from nutrient to nutrient. Some vitamins and minerals become diminished when cooked, while others may become more readily available. More research is also needed to know whether differences between raw and cooked produce are actually enough to affect mood and mental health, the researchers wrote.
Cynthia Sass, RD, Health’s contributing nutrition editor, says she’s not surprised that this study found that raw produce is tied to better mental health. “The importance of eating enough produce is immense, and involves both physical and emotional well-being,” says Sass, who reviewed the new study but was not involved in the research. “We also know that certain nutrients are vulnerable to heat, including vitamin C and B.”
It’s not practical to eat all of your produce raw, says Sass. But luckily, specific cooking methods and prep techniques can also affect how well a food retains its nutrients. For example, cutting up carrots after boiling (instead of before) can boost certain nutrients by 25%. “Chopping carrots increases the surface area, so more of the nutrients leach out into the water while they are being cooked,” she says. “By cooking them whole, you lock in more.”
Consuming vegetables with healthy fats, like avocado or extra virgin olive oil, also greatly increases the absorption of certain antioxidants, she adds. But the most important goal for upping your nutrient intake—and for supporting mental health while you’re at it—is to simply eat more vegetables each day, she says.
“The power of produce is real and far reaching,” says Sass. She recommends aiming for at least three (and ideally five) baseball-sized servings of veggies every day.
“Fresh and raw are fantastic for your health, but if including both raw and cooked veggies is a more practical way to hit the mark day after day, mix it up,” she says. “The benefits of eating frozen, cooked veggies, or even canned outweigh not eating them at all.”
