Originally printed in the May 2018 issue of Produce Business.
By Redzo Mujcic and Andrew J. Oswald
Read Jim Prevor’s Commentary below
Fruits and vegetables are known to provide important health benefits. Yet, in Western society, the typical citizen eats an unhealthy diet. The difficulty of persuading people to consume more fruits and vegetables remains a serious one.
In this study, we uncovered evidence consistent with a longitudinal connection between the consumption of certain foods (especially fruits and vegetables) and later subjective well-being, and a channel that appears to be independent of long-run health.
In disciplines beyond public health research, the study of happiness and well-being has focused on the role of economic, personal and political influences. It is perhaps understandable that the role of food in the list of determinants of well-being has so far been given little attention.
We used a panel of 12,389 individuals (ages 15–93) to trace potential linkages running from diet to later-life satisfaction and happiness. The analysis was done by following individuals between 2007 and 2013.
This article documents the longitudinal linkages between produce consumption and mental well-being; such an approach ensures that any observed relationship is not merely a cross-sectional pattern caused by omitted factors such as personality, wealth or family upbringing.
Two questions relating to produce consumption were available in 2007 and 2009 of the Household, Income, and Labour Dynamics in Australia (HILDA) Survey, a nationally representative panel survey that began in 2001. The corresponding questionnaires asked: “Including tinned, frozen, dried and fresh fruit, on how many days in a usual week do you eat fruit?” and “Including tinned, frozen and fresh vegetables, on how many days in a usual week do you eat vegetables?” with possible responses ranging from 0 (“do not eat any fruit or vegetables in a usual week”) to 7 days per week.
For those who responded with some positive frequency to these questions, the following was asked: “On a day when you eat fruit, how many servings of fruit do you usually eat?” and “On a day when you eat vegetables, how many servings of vegetables do you usually eat?”
Data are collected each year by face-to-face interviews and self-completion questionnaires. The first technique is mainly used to gather the demographic and socioeconomic information, and the latter is adopted to measure health and lifestyle choices. The survey respondents were shown flashcards to visually define a serving size or portion. The mean value was 3.84 servings per day, with a standard deviation of 2.01.
The first dependent variable examined was self-reported life satisfaction, derived from the question, “All things considered, how satisfied are you with your life?” Respondents were told to “Pick a number between 0 and 10 to indicate how satisfied you are.” Overall, the mean score for the sampled individuals in Australia was 7.91, with a standard deviation of 1.41.
As an additional check, we used a second measure. The respondent was asked, “How much of the times in the past 4 weeks” did he or she experience particular types of feelings or symptoms, including “been a happy person.” The individuals’ responses were coded from 1 (none of the time) to 6 (all of the time), with a mean happiness score of 4.43 out of 6.
A so-called fixed-effect regression equation depicts the (uncorrected) longitudinal relationship — the change-on-change relationship — between subjective well-being and nine different levels of produce consumption. The regression analyses provide formal evidence implying that a change from the lowest levels to the highest levels of consumption would, on average, be associated with a rise in life satisfaction of approximately 0.24 life-satisfaction points.
The implied effect size is substantial. At first glance, 0.24 might be thought to indicate that the consequences of fruit and vegetable intake are minor. That interpretation is mistaken; it stems from a blurring of the distinction between interperson variance and intraperson variance.
As in much of the longitudinal public health research, in this study we tried to understand not the (inevitably high) cross-sectional variation in human well-being — for example, someone becoming richer through time and becoming happier and simultaneously eating in a healthier way because they could now afford it, or divorcing a spouse and becoming less happy and also eating in a less healthy way — but instead intraperson changes that might be influenced by public interventions.
The effect is the equivalent in absolute size to (a negative direction) that of becoming unemployed or approximately half the size of the emotional consequence of marital separation. Such an effect size is large. An open issue is whether diet might have slow-acting effects on mental well-being. The analyses explore this. The regression equations reveal that produce consumption in the current year is predictive of higher well-being — measured as life satisfaction or as happiness — in the future even after control for current well-being. The first dependent variable is life satisfaction. The second variable is “been a happy person.”
These findings are consistent with the idea that eating certain foods is a form of investment in future happiness and well-being. The implications of fruit and vegetable consumption are estimated to be substantial and to operate within the space of 2 years—too quickly to be a reflection of the physical advantages of diet for outcomes such as cardiovascular disease documented by earlier researchers.
In a sense, this article offers a new possibility for future public-policy programs to encourage healthy eating — the possibility that citizens in Western society could be given evidence that happiness gains from healthy eating may occur much more quickly than any long-distant improvement to people’s physical health.
If individuals weigh the likely benefits of fruit and vegetables in their diet, and set that against any perceived costs, both pecuniary and nonpecuniary, of doing so, then scientific evidence of extra psychological gains from a healthy diet might help to persuade people to raise their intake of fruit and vegetables.
Redzo Mujcic (left) is with the Faculty of Health and Behavioural Sciences, University of Queensland, Brisbane, Australia. Andrew J. Oswald (right) is with the Department of Economics and Centre for Competitive Advantage in the Global Economy, University of Warwick, Coventry, United Kingdom. “Evolution of Well-Being and Happiness After Increases in Consumption of Fruit and Vegetables” American Journal of Public Health August 2016; 106(8): 1504-151 Copyrighted by American Public Health Association
Before We Promote Produce As The New Prozac…
By Jim Prevor
This study from our friends Down Under is an important one. But its implications may not be as “happy” as first impressions might indicate. The gist of the study is these researchers have found evidence people who are eating diets rich in fruits and vegetables are happier people – or have greater life satisfaction – than people who eat fewer fruits and vegetables. Furthermore, this happiness imbues people’s lives long before any actual health consequence to higher consumption of produce would have manifested itself. So, it is not a function of people eating more produce simply becoming happier because they have a lower incidence of diabetes or atherosclerosis, etc.
The first instinct is to say these researchers have stumbled on a great marketing edge for the produce industry. We know “nannyish” admonitions to eat your greens because of health outcomes has been of very limited effect. But, now we may be able to market not only these long-term health effects but also a shorter-term lift. In fact, the Produce for Better Health Foundation already has started mentioning this research in its ads in this publication.
Perhaps we could go further and market produce like some kind of natural Prozac – a pill to make you happy. And if this is true, surely just a bit more research will leave us to more specific claims. After all, don’t happier people have better friendships, more cheerful spouses and children, more satisfying sex lives? The marketing claims practically write themselves.
Indeed, perhaps, as such research is expanded and its results duplicated, the industry and public health authorities may well latch on to such claims to promote produce and, possibly, with some effect.
So maybe that person who is eating most healthily is happier because his life prospects are better.
Yet, there is something in this research that suggests the possibility of something more profound. One of the reasons the many health-oriented messages aimed to boost consumption of produce have failed is because they treat the processing of information about produce as some kind of independent variable. So, we like to believe if we educate consumers about the health benefits of eating produce, they will eat more and derive these benefits. Done on sufficient scale, the diets and health of the populous will be transformed.
Indeed, this is a pattern public health efforts on cigarettes have taken. But this may be the exception that proves the rule. On January 11, 1964, the Surgeon General of the United States came out with his famous report on smoking. More than a half a century later, with enormous repetition of the public health message against smoking, legal changes to reduce access to cigarettes, such as bans on vending machines, enormous taxes imposed on the sale of cigarettes and deep cultural changes making it much less acceptable to smoke or to expose people to secondhand smoke – there are no smoking sections on planes or in movie theatres, for example. And in the end, smoking has been reduced. Yet, as the CDC explains, even today:
Cigarette smoking is the leading cause of preventable disease and death in the United States, accounting for more than 480,000 deaths every year, or about 1 in 5 deaths. In 2016, more than 15 of every 100 U.S. adults aged 18 years or older (15.5 percent) currently* smoked cigarettes. This means an estimated 37.8 million adults in the United States currently smoke cigarettes. More than 16 million Americans live with a smoking-related disease.
Back in 1964, about 42 percent of adult Americans smoked, so this is a big achievement. But the benefits accrued by eating more produce are much more opaque than the risks accrued by smoking cigarettes. The odds of an effort as intense and extended as what we have seen to discourage smoking versus encouraging produce consumption are not particularly good.
However, in the smoking data, there is something that might be relevant: Here is a list of smoking prevalence by certain educational categories:
- Nearly 41 of every 100 adults with a GED certificate (40.6 percent)
- Nearly 20 of every 100 adults with a high school diploma (19.7 percent)
- Nearly 19 of every 100 adults with some college (no degree) (18.9 percent)
- Nearly 17 of every 100 adults with an associate’s degree (16.8 percent)
- Nearly 8 of every 100 adults with an undergraduate degree (7.7 percent)
- Nearly 5 of every 100 adults with a graduate degree (4.5 percent)
What these numbers indicate is that the world sends people all kinds of clues as to how to be a success in life. Go to school, don’t smoke, do drugs or drink alcohol to excess. Don’t have a baby without being married, on and on.
Some people simply have a better ability than others to absorb this information, and they are the people more likely to succeed in life. This is why education focused on getting people to eat more produce is so difficult. How can you have a person who smokes cigarettes, does drugs, gets drunk regularly, drops out of high school, has unprotected sex and children without marriage … how can one expect a person so bad at absorbing the wisdom of the world to, somehow, single out the lesson that he or she should eat more fruits and vegetables?
So maybe that person who is eating most healthily is happier because his life prospects are better. He happens to be capable of absorbing public health and other recommendations. In other words, maybe it is not eating more produce that makes him happier; it is that people better equipped to succeed in life also eat more produce. The research is fascinating, but there is more work to be done before causality is established.