Back in 2012, Dr Tamlin Conner was conducting a three-week diary study on the relationship between different foods and moods. During this study, she found a connection between fruit and vegetable consumption and reports of happiness, which she describes as one of the strongest associations she has ever seen in her data.
Conner has since continued to research the links between fruit and vegetable consumption and emotional wellbeing.
“At that stage there was quite a bit of research linking fruit and vegetable consumption as part of a wider Mediterranean diet to lower depression … around the same time there were a couple of studies that showed using population level data that higher fruit and vegetable consumption was related to greater psychological wellbeing, as measured by life satisfaction and happiness.”
What was unknown at the time was causation. Does eating healthier food give people the nutrients the brain needs to help create serotonin, dopamine and other neurotransmitters linked to mood? Or are people less likely to eat fruit and vegetables if they are in a worse mood?
“In the last couple of years, intervention studies have shown that increasing your intake of fruit and vegetable consumption can in turn have positive benefits to your wellbeing,” says Conner.
“Importantly, these relationships still hold even when you control for other demographic and health characteristics like socioeconomic status, gender, smoking, body mass index, chronic health conditions and so on. There seems to be quite a strong link between intake of these healthy foods and greater psychological wellbeing.”
She recently published a study which showed a stronger correlation between the intake of raw fruit and vegetables with better mental health than consumption of canned or processed fruit and vegetables.
“That was only a correlational study so I can’t be sure about causation, but if I was a betting person I think the more that you eat the fruit and vegetables in their more unprocessed state, the better. Of course there are exceptions – you need to cook certain vegetables, like potatoes, you can’t eat them raw and there are certain vegetables like tomatoes that might have better health benefits when they are cooked, but those are more exceptions rather than the rule.”
Her research has found a slight difference between the effects of fruit versus vegetables, when it comes to their impact on psychological wellbeing
“For the most part both are equally contributing. In one or two of my studies, fruit had the slight edge, but it wasn’t significantly different,” she says.
“In terms of the five-a-day recommendations, it is recommended to eat two servings of fruit and three servings of vegetables, so there is a prioritisation of vegetables because fruit is very calorie dense.”
Although research has found a definite link between higher fruit and vegetable consumption and better mental wellbeing, there are many other factors which may have an impact on a person’s psychological health.
“There are so many other things that are travelling along with poor [eating] habits since the 1970s, such as lack of physical activity and occurrence of sugar – a high sugar diet has also been linked to inflammation which has been linked to depression, so that’s independent of fruit and vegetable consumption,” Dr Conner says.
“I found, for example, sleeping habits can be the single biggest predictor of wellbeing in terms of health habits. Sleeping is big, and then diet comes second to sleeping.”
When asked if New Zealand’s high rates of depression could be linked to poor consumption of fruit and vegetables, she could not be certain.
“The problem is that all countries’ rates of depression are going up and our dietary habits are getting poor…I can’t say how much of the increase in depression is due to diet, but probably some proportion of it is. That’s a really important question.”
There is good evidence to suggest that modifiable lifestyle habits, like diet, exercise, sleep and reductions in stress, can go a long way towards improving psychological wellbeing, Dr Conner says.
“It’s something that we can control or at least do ourselves, as opposed to trying to change genetic dispositions or trying to change the social media environment or trying to do other things to address the mental health crisis. Choosing to eat a banana instead of a candy bar is something that you can do on a day-to-day basis that could help.”
Top 10 raw fruit and vegetables related to greater psychological wellbeing*
- Dark leafy greens (spinach, kale)
- Citrus fruits
*from ‘Intake of raw fruits and vegetables is associated with better mental health than intake of processed fruits and vegetables’ by Kate L. Brookie, Georgia I. Best, and Tamlin S. Conner, Frontiers in Psychology, 2018
Mental Health Awareness Week (MHAW), runs from 8–14 October 2018. This year’s theme is ‘Let nature in, strengthen your wellbeing – Mā te taiao kia whakapakari tōu oranga’.
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