Live life with gusto

For a change, we consider an Australian study (European Journal of Clinical Nutrition, (2015) 69, 585-591) rather than drawing on research conducted elsewhere. Here is their summary of the work:

There is continued interest in the effect of diet on the incidence and severity of depression, and several studies investigating this relationship have focused on individual dietary factors or diet patterns.  In the present work we studied the association between fruit and vegetables and depressive symptoms in the midage cohort of the Australian Longitudinal Study on Women’s Health.  A total of 6271 women with a mean age of 55 years were followed up at three surveys over 6 years.  A score of 10 or more on the Centre for Epidemiological Studies Depression-10 scale indicated depressive symptoms.  Fruit and vegetable intake was assessed using short questions.  A total of 381 women (6%) were depressed at all three surveys over the 6-year survey period.  Cross-sectional logistic regression analysis showed a reduced prevalence of depressive symptoms (odds ratio of 0.86) among women who ate 2 or more pieces of fruit/day, even after adjustment for several factors including smoking, alcohol intake, body mass index, physical activity, marital status, education level, energy consumption, fish intake and other co-morbidities. The predictive model also showed a reduced incidence of depressive symptoms (odds ratio of 0.82) among women who ate 2 or more pieces of fruit/day.  There was also an association between vegetable consumption and prevalence of depressive symptoms but at higher levels of intake.  We conclude that increasing fruit consumption may be one important means of reducing the incidence of depressive symptoms in middle-aged women.

They also made the following points:

A Global Burden of Disease Study has reported a 37.6% increase in mental disorders and substance abuse since 1990, and it’s estimated that by 2030 depression will rank in the top three disorders for global disease burden. This study also estimated that a diet low in fruit is the most prominent dietary risk factor for global disease burden, contributing to an estimated 4.9 million deaths pa and 4.2% of global disability adjusted life years (ie years of healthy life lost).
With increased focus on dietary patterns in studies of disease causation or prevention, fruit and vegetable intakes are almost always grouped together when evaluating associations with health, but this approach does not allow assessment of any differential activity between the two food classes.
Participants were asked ‘how many pieces of fruit do you usually eat/day’, and ‘how many serves of vegetables do you eat/day’; a serve of vegetables was equivalent to half a cup of cooked vegetables, one cup of salad vegetables or one small potato.
Incidence of depression was defined as the presence of depressive symptoms at a particular survey and the absence of depression immediately before it. Prevalence was defined as presence of depression at any of the three surveys.
6271 women out of 10629 completed all 3 surveys with no missing data. Women who were consequently excluded had lower educational attainment, were more likely to smoke, be sedentary, have a higher body mass index and were more likely to have depressive symptoms.
Only 2.7% of women ate the recommended 5 or more servings of vegetables/day at all 3 surveys, and only 2% ate 5 serves of vegetables/day and 2 pieces of fruit/day.
For vegetables, prevalence was only significant at higher consumption levels, and for incidence, there was no clear effect.
Diet has an effect on mood, and in cross-sectional studies it’s not clear whether poor diet increases depression or vice versa, eg pre-existing depression before the 3 surveys began could have led to poor diet during the study (reverse causation). This is why the authors placed more emphasis on incidence than prevalence as in this case depression only occurred after diet had been recorded and the study had begun.
Women who were excluded from the study were less health conscious and more likely to be depressed, so it might be expected that if included, the results would have been more pronounced.

The following independent comment can also be added:

Further pertinent findings from the 2013 Global Diseases study were that mental and substance abuse disorders accounted for 0.5% of all years of life lost through death (YLL) and 22.9% of years lost through disability (YLD), with depressive disorders accounting for 40.5% of the combination of these YLL and YLD figures. Mental and substance abuse disorders were the leading cause of YLDs worldwide.
The focus on women in the above study has particular relevance given women are twice as likely to suffer from depression as men.
Eating 2 or more pieces of fruit/day had a positive impact on the incidence of depression (-18% risk), but to put this in perspective with other non-dietary factors that would have a predictable negative impact, the above study reported divorce/separation/widowed increased risk by 24% and smoking more than 20 cigarettes/d by 49%.
Studies on beneficial effects of individual nutrients on depression such as folate, vitamin B, C, D and E, and n-3 polyunsaturated fatty acids have generally been inconsistent. This is not really a surprise as foods in the diet are eaten in combination with many others and they all have multiple interacting effects of varying magnitude. Even though the above study found that fruits reduced incidence risk by 18%, it might be expected that considering whole healthy dietary patterns rather than singling out fruit or vegetables might confer even stronger benefits. And this in fact was found in a 2010 Japanese study where they identified a healthy Japanese diet that included high intake of fruit, vegetables, soy products, mushrooms and green tea which reduced depression risk by 56%. Similarly in a 2009 British study, participants in the highest tertile of a whole foods diet (fruit, vegetables and fish) had 26% less risk of depression 5 years later and after allowance for possible confounders. In contrast, those with the highest consumption of processed foods (desserts/biscuits, processed meats, chocolate/sweets, refined grains, quiche/pie, high fat dairy and condiments) had an increased risk of 58%.

In conclusion, this Australian study suggests fruit has more marked preventive effects than vegetables on the incidence of depression, but the best policy, as always, is to eat a balanced and varied healthy whole foods diet.