When your mom told you to eat your veggies, she probably explained that these foods help you grow up big and strong. Turns out, they help you grow up happy, too.

That's the conclusion of a large new study out of the U.K. that tracked 14,000 Brits to determine fruit and vegetable consumption's effects on happiness and well-being. The research team wanted to know not what eating your carrots and cauliflower and apples could do for your body, but what effects they had on a cluster of characteristics related to mental well-being: optimism, happiness, high self-esteem, and relationship quality.

The researchers found that "fruit and vegetable intake may play a potential role as a driver, not just of physical, but also of mental well-being in the general population." Among those study subjects that hit the five-a-day target set by UK nutritional guidelines for fruit and vegetables, 33.5 percent had high mental well-being. Among those who consumed just one portion, only 6.8 percent were doing so well mentally.

Correlation or Causation?

By itself it's an intriguing finding, but one could rightly wonder if this association between eating your greens and feeling your best mentally is a matter of causation or just correlation. Maybe, for instance, the sorts of people who can afford to buy and prepare all those fruits and veggies happen to also have less stressful and happier lives than those who struggle to get their recommended daily intake.

But as PsyBlog points out in its write-up of the research, there are reasons to believe that eating the good stuff actually boosts mood. "Although this study only tells us that fruit and vegetable consumption and higher mental well-being are associated, other studies have shown a stronger connection. One asked participants to log how many fruits and vegetables they ate over a 21-day period, as well as their mood. The researchers found that eating more fruit and vegetables one day predicted better mood the next day," the blog points out.

The takeaway, therefore, is pretty much a no-brainer. Heed the advice of good old Mom and start loading up your plate with plenty of fruit and vegetables. As study co-author Sarah Stewart-Brown concludes, "Mental illness is hugely costly to both the individual and society, and mental well-being underpins many physical diseases, unhealthy lifestyles, and social inequalities in health …  [high] fruit and vegetable intake could [enable] people to enhance their mental well-being at the same time as preventing heart disease and cancer."

How does your fruit and vegetable consumption measure up against the recommended daily intake?