September, 2017

Research Perspective and Comments & Analysis

More Produce Potential: Combined Benefits For Mental Health And Smoking Cessation

By Jeffrey P. Haibach, Ph.D., Mph, Health Science Officer, U.S. Department Of Veterans Affairs

Research supporting the benefits of eating produce is endless, yet new reports come out regularly with added support. There is overwhelming research that eating a diet high in produce is associated with better health — physical, mental and possibly even spiritual. There is further research on inverse associations between produce and addictions, where high produce intake is associated with lower addiction. Other research connects addiction and poorer mental health.

In one study, we assessed these phenomena of triangulation between produce intake, mental health and addiction. Looking specifically at depression and cigarette smoking, smokers with a depression history have lower odds of quitting; depression symptoms mirror smoking withdrawal symptoms; and higher produce intake is known to have an inverse association with both depression and smoking. In our study we found produce intake (measured as fruits and vegetables) moderated the association between depression and cigarette smoking. That is, among persons with higher produce intake, depressive symptom history appeared to be removed as an impediment to smoking cessation over a four-year follow-up period.

We found the threshold for these results to be fairly low, where eating produce at least once per day seemed to make the difference in removing depression symptoms associated with quitting smoking over time. In another statistical model, we found the association between depression symptoms and smoking frequency to be mitigated at eating produce about five times per day. This produce intake frequency threshold is interesting, as it mirrors the five servings per day recommendation, which could merely be coincidental. There also may be an underlying biological basis that transcends various health benefits at that frequency or volume. In a prior study in a different study sample, we also found similar thresholds for smoking frequency and smoking cessation based on produce intake.

There are many limitations to this, and in our prior study, they were largely observational health studies of smokers on various health-related factors. In the latest study, when smokers were followed up four years later, we assessed whether or not they had quit smoking based on their level of fruit and vegetable consumption and depressive symptoms at baseline. To ensure our findings weren’t explained by higher health consciousness by those who ate more produce simply explaining a higher quit likelihood, we adjusted for overall health-related lifestyle via exercise, heavy alcohol use and illicit drug use, and the associations persisted.

Overall, the results of this study paired with other studies cited in our research paper and suggest opportunities to promote produce consumption to help improve mood, mental health and reduce addictions. In looking at the underlying neurobiology, both smoking and consumption of sweet-tasting foods, such as fruit, promote dopamine release and feelings of pleasure (positive affect) and reduce negative affect. This promotes or inhibits some depressive symptoms. Either behavior could reduce the desire to consume the other, such as has been observed where eating fruit can reduce perceived enjoyment of a subsequent cigarette (e.g., make the cigarette taste worse).       

Chemicals in fruit also interact with the dopaminergic system. Serotonin is further known to mediate the effect of dopamine and moderate mood and feelings of negative affect. Both fruits and vegetables and smoking have been found to be monoamine oxidase inhibitors (MAO), which increase levels of dopamine and serotonin by inhibiting the action of monoamine oxidase. Higher fruit and vegetable intake could be hypothesized to act as an alternative MAO to smoking, thereby attenuating or possibly eliminating the smoking depression association.

In considering the underlying neurobiology, higher produce intake may buffer the depressive withdrawal symptoms of smokers, thus reducing withdrawal symptoms as an impediment to cessation. Smokers are also known to reach for a cigarette when having negative feelings, whereas fruit intake can promote positive feelings. Thus, if a person eats fruit in moments of negative or depressive feelings, he/she may be less likely to reach for a cigarette. In essence, eating produce may make it easier for smokers to quit, especially those who struggle with depression or intense withdrawal symptoms when trying to quit.

Overall, the concept of improving mood and quitting harmful habits such as cigarette smoking could help promote produce intake. The business of produce may be the anti-cigarette. There are so many reasons to promote produce; it’s a good business.

Jeffrey Haibach, Ph.D., MPH, is a Health Science Officer and Scientific Program Manager. Prior to his transfer to the central office of the U.S. Department of Veteran Affairs, he served at the VA HSR&D Center for Health Equity Research and Promotion in Pittsburgh. In other federal positions, he served in research with the U.S. Department of Agriculture and on active duty in the U.S. Army as a senior non-commissioned officer. He has conducted collaborative research and other work in diverse settings, including clinical, community and public health venues with associates from governmental, academic, faith-based, corporate for-profit and non-profit organizations. His primary research interests are in health promotion, multiple health behavior change and the potential of wellness approaches for addiction prevention, treatment and recovery.


Only More Research Will Prove A Causal Relationship

In the many years these analyses of research have been written, there have been countless glimmers of hope citing new and compelling reasons for people to eat more produce. Yet, in the end, only the fewest have come to be “generally accepted.”

The reason is found in one word: associated. When Dr. Haibach explains that, “There is overwhelming research that eating a diet high in produce is associated with better health — physical, mental and possibly even spiritual,” it makes our hearts sink, for the truth is this kind of association leaves us with an overwhelming desire to do a lot more research and see if we can establish a causal relationship.

The dilemma isn’t hard to notice. We study people and find out those who eat a lot more fresh fruits and vegetables are less likely to be depressed than those who do not. Does this mean produce is an effective tool to fight depression? As Ernest Hemingway wrote: “Isn’t it pretty to think so?”

Yet, isn’t it just as likely, maybe more likely, that people who are not depressed will take better care of themselves, and that overall happiness expresses itself in a multitude of ways? These people exercise, stay hydrated, use sunscreen and eat more healthfully — which includes eating more fruits and vegetables. Now researchers can try to adjust for these variables, but we are relying on self-reporting by people as to whether they do these healthy things or conversely, unhealthy things, such as drug use, abuse of alcohol, etc.

The problem is that asking people about these habits is not a neutral question. It is not like asking if they prefer vanilla or chocolate. It is, in fact, like asking them if they are smart people. The temptation to lie is significant.

Studies that identify associations are valuable, but they have to be interpreted in the context of understanding that there are many other associations. So, consumption of produce, for example, rises with income and education, which means if a researcher finds something correlates with higher produce consumption, it almost certainly correlates with higher income and educational levels.

The quality of data is also important. Is this a study where the research subjects self-report whether they do drugs, engage in risky sexual behavior and drink excessively — or is this a study where blood tests are frequently given and other steps are taken to monitor actual behavior?

Even produce consumption levels are questionable under self-reporting. Are grocery receipts monitored and other steps taken to ascertain the veracity of these reports? After all, produce consumption is so widely recognized as a good thing — a virtuous behavior — that maybe what we are finding is people who care about how they are perceived, will “gild the lily” about produce consumption. These same people could also be the ones who will care enough about how they are perceived by friends and co-workers that they will quit smoking rather than be thought of poorly.

Then there is always the flip side of the coin. This research points out that due to the fact that eating fruit can promote positive feelings, people suffering from depression or experiencing negative life events might be less likely to reach for a cigarette if their habit is to reach for some fruit. This would be fantastic news. Yet, it is also true that lots of people hesitate to give up smoking because they fear gaining weight if they do. And isn’t eating sweet fruit to squash feelings of inadequacy almost the definition of nervous eating?

Of course, all the benefits of eating produce identified in this research piece could be true just as many other benefits associated with eating produce could be true. Yet, reading these research reports for years has led me to think that a better way of looking at these things is to remember there is no silver bullet. Mostly, people who tout specific benefits from eating this or that are, to be generous, speaking without adequate evidence to prove their cases.

A better way to consider these matters is that life is a seamless web. Just as you can’t spot reduce and get rid of, say, belly fat, by doing lots of sit-ups, so there is rarely one food that magically cures some ailment or alters one’s personality. The mental and physical work together; and if you are open to good ideas, open to the messages that society passes on about who will be healthy and who will be successful in life, then you will do many things right, including eating more fruits and vegetables. If you are deaf to such messages, then the odds you will choose eating more produce as the singular virtue you adopt are slim odds indeed.