An Australian study has found that encouraging young people (18-25) to increase their servings of fruit and vegetables every day can improve their mental health and reduce symptoms of depression and anxiety. The study was published in PLoS One, which is a peer-reviewed open access journal.
The scientists acknowledged that previous studies had examined the benefits of increased consumption of fruit and vegetables with reduced risk of some cancers, increased longevity and with better cardiovascular health. There are some studies that now link healthy eating with better mental health, including lower symptoms of anxiety and depression, higher life satisfaction, great social-emotional well-being and greater happiness. This suggested that the benefits of increased fruit and vegetable consumption could go beyond physical health, however the studies had failed to prove a causal link conclusively with mental health, or had not separated out the use of fruit and vegetables from that of olive oil or oily fish.
The study recruited low fruit and vegetable consuming young adults who reported eating less than 3 combined servings of fruit and vegetables a day, which is lower than current guidance which suggests 5 servings a day. Young adults were selected because they typically eat the lowest amount of fruit and vegetable servings and they are beginning to gain independence over their health behaviour. The trial took place over two weeks and selected participants who were not on anti-depressant medication. They had not been diagnosed with mental health issues.
This randomised trial split the 171 participants into 3: a control group who were asked to continue with their regular diet, an intervention group which given fruit and vegetable vouchers and were sent text messages twice daily which used a number of behavioural change techniques to encourage them to increase fruit and vegetable consumption to at least 5 servings a day or a group that were given a bag of two weeks’ worth of fruit and vegetables and who were asked to consume at least two additional servings (one each of fruit and vegetables) on top of their normal daily fruit and vegetable consumption. The participants’ food consumption was reported nightly, using a smartphone survey. Blood tests were also used to measure vitamin C and plasma carotenoid levels. Depressive and anxiety symptoms were measured before and after the trial. Positive and negative mood, vitality and flourishing were measured nightly through a smartphone survey to minimise memory-based reporting and maximise sensitivity to detect differences in mood and well-being as they changed over time. The scientists predicted that the two groups who had been asked to increase their consumption of fruit and vegetables would show stronger measures of well-being. Flourishing behaviours were questions that measured curiosity, creativity and motivation. The scientists also examined whether higher levels of vitamins could help people to feel better.
The researchers found that giving the young adults the two week supply of fruit and vegetables improved several aspects of their psychological well-being over the two week period. They showed improvements in feelings of vitality, flourishing and motivation, even though the trial was only short. This was quite a rapid improvement. The group who were sent motivational texts did not seem to show corresponding benefit. Both groups were given a similar amount of money - $10 voucher or $10 value of fruit and vegetables, but the second group did not show the same amount of improvement. The researchers suggested that this could be due to lack of control over how the money was spent. The second group were more likely to eat cooked vegetables in casseroles or mixed into the main meals. The first group chose to eat a lot more of the produce raw and had been provided with high-quality products.
The text message group reported that the text messages had not been intrusive or annoying and that they had found them helpful in reminding them to eat more healthily. The researchers noted that during a previous study that had distributed free fruit and vegetables, participants had been reluctant to waste the food and had made efforts to ensure that it was all consumed. This offered an internal motivation to consume the fruit and vegetables which can be more rewarding and can lead to greater well-being. There were significant changes over the two week period to well-being although the participants did not all achieve the 5-a-day serving. Even small improvements to diet seemed to increase well-being and mental health attitudes. The scientists surmised that if 5-a-day had been achieved, then even more improvements to well-being may have been seen. Bigger increases in consumption would be required for further studies. The scientists pointed out that there had not been a longer term follow-up for the participants. They suggested that longer term studies should be instigated into the link between mental health and fruit and vegetables for a longer period of time and on a larger scale.
Conner, T.S., et al., Let them eat fruit! The effect of fruit and vegetable consumption on psychological well-being in young adults: a randomised controlled trial, Feb 2017, PLOS One, open access study