A UK study links eating fruits and vegetables with happiness and confidence.
A recent longitudinal study, published in the February issue of Social Science & Medicine, has linked the consumption of fruits and vegetables with better mental health. Associations between a healthy diet and better general health, of course, are nothing new. For instance, a 2014 systematic review of prospective cohort studies found eating fruits and vegetables is linked with reduced risk of all-cause mortality—potentially because fruits and vegetables include beneficial chemicals: antioxidants like vitamin C, and phytochemicals such as carotenoid and flavonoids. But is eating fruits and vegetables also associated with better mental health? That is what the present study by Ocean and colleagues attempted to answer.
An investigation of fruit and vegetable consumption and mental well-being
Data for this study came from the UK Household Longitudinal Study (UKHLS), which includes information on over 45,000 people (aged 15 years and over). Only data from waves 2, 5, and 7 were used because in other waves participants were not asked about how often they ate fruits and vegetables, and/or how many portions were consumed (on days when at least one portion was consumed; henceforth called “positive consumption days”).
The primary outcome was mental health, which was assessed using a shortened version of the General Health Questionnaire called GHQ-12.
GHQ-12 measures various aspects of mental health, such as self-worth, self-confidence, worry, sadness, and happiness.
To control for possible confounds, researchers collected data on participants’ health conditions and lifestyle (such as smoking or walking); they also gathered information on potential predictors of well-being (such as gender, age, relationship status, education, the number of children, and income).
The relation between eating healthy and factors like income, age, and sex/gender
Descriptive statistics revealed several patterns.
One, most people (78 percent) did not consume the recommended five portions of vegetables/fruits.
Second, there was only a weak association between income and fruits and vegetables intake: Those with the highest income ate fruits and vegetables somewhat more frequently than those with lower income.
The authors speculate that the reason income had a minor impact was that other factors contribute to healthy eating habits too. For instance, people might choose fast food overcooking a healthy meal at home not only because of financial concerns but also lack of time.
Third, healthy eating was associated with age non-linearly: Initially, the intake of fruits and vegetables increased with age. For example, on positive consumption days, only 13 percent of 15- to 29-year-olds but twice as many 53- to 65-year-olds ate the recommended five portions. This trend, however, reversed after age 64 and decreased again (e.g., 16 percent in those 86 years and older). One explanation is that retirement (in the UK, between ages 65 and 68 years) results in less activity and less calorie intake.
Nevertheless, the frequency of eating at least one portion of fruits and vegetables continued to rise into old age; fruit consumption frequency continued to rise even after age 80 years.
Fourth, compared to males, females consumed fruits and vegetables more frequently and in a greater quantity. The reasons for this are not clear. Perhaps women, compared to men, are more health-conscious or more likely to be vegetarian. Another possibility is that women over-report healthy food intake because (compared to men) they feel a stronger pressure to provide socially desirable answers during research interviews.
Vegetable/fruit consumption and mental well-being
Using regressions analyses, the authors attempted to estimate the relationship between mental well-being, and both the quantity of fruits and vegetables consumed (on positive consumption days) and the frequency of fruits and vegetables consumed. A regression of mental well-being on vegetables and fruits showed a positive and statistically significant relationship (even after controlling for demographic variables).
The frequency of fruit and vegetable intake was associated with higher mental well-being; this effect was slightly stronger for vegetables than fruits.
The quantity of fruit and vegetable intake also had a positive association with mental health. On positive consumption days, increasing fruit and vegetable intake by just one portion was correlated with an increase in mental well-being of 0.133 units (p<0.01).
What does the 0.133 unit mean, practically?
Based on their data, the authors suggest the following two comparisons: On a positive consumption day, consuming five portions means 0.67 units increase in mental well-being. That quantity is equivalent, in negative terms, to loss of mental well-being seen in changes related to widowhood (-0.68 units).
Alternatively, increasing one’s consumption by a single portion (on positive consumption days) is equivalent to walking 10 or more minutes for an additional 8 days per month.
The results of the current investigation are comparable to previous studies, such as a 2016 investigation of over 12,000 Australians. That study found increasing fruit and vegetable portions by eight per day is equivalent to increases in life satisfaction from unemployment to employment.
Takeaway: Adding fruits and vegetables to your diet
While the above associations do not prove causation, they do suggest significant links between consuming fruits and vegetables and attaining better mental health.
Compared to some health-related changes (such as quitting smoking or jogging each day), consuming more fruits and vegetables is easier and less time-consuming. And unlike medications, fruits and vegetables do not have a long list of negative side effects. In short, adding fruits and vegetables to your diet may be a safe bet. So, try a variety of vegetables and fruits (the colors of the rainbow) and pick a few favorites. Then, incorporate them into your diet. Start small, perhaps by adding a piece of fruit to your breakfast, and go from there. Oh, and bon appétit!
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