Fruit and vegetables: still surprising!

Implications of F&V intake on depression and cigarette smoking

Knowledge continues to expand on the benefits of fruit and vegetables (F&V) intake for health. There is longstanding evidence that a diet high in F&V is protective against chronic disease, mental illness, and promotes overall physical and mental health1,2. As we discuss in this article, several recent studies suggest that F&V might influence tobacco and drug use prevention. We further outline possible neurobiological and psychological mechanisms of explanation.

F&Vs, depression, and cigarette smoking

Through background literature review in the study this article is based on, we present a history of research finding inverse associations between F&V and cigarette smoking, F&V and depression, as well as depression and smoking cessation. For example, F&V intake has been associated with depressive symptom reduction3, smoking cessation4, and persons with a depression history have been found to have a lower odds of quitting smoking than persons without a depression history5.

F&V moderates the depressive symptom and smoking association

In our recent study, we found that among smokers with higher F&V intake, there was no association between depressive symptoms and smoking frequency, nor with smoking cessation over time. However, among smokers with lower F&V there was a positive association between depressive symptoms and smoking frequency and an inverse association with smoking cessation. That is, among smokers with lower F&V intake, those with higher depressive symptoms smoked more and had a lower likelihood of quitting smoking over time. These associations persisted after adjustment for other health-related behaviors and common demographics.

The cut-off for the moderation effect with smoking frequency, in crosssectional analyses, was further aligned with general recommendations for F&V intake at 4.9 times per day. This could correlate coincidentally or scientifically with the general 5 servings or cups per day recommendation for F&V intake. The longitudinal threshold was very low at F&V 1.2 times per day in association with smoking cessation. This aligns with our earlier study among a different national sample where we observed a longitudinal  low threshold for effect (F&V 1.9 times per day) for an association with smoking cessation4. We also observed in the prior study that F&V was inversely associated with 3 different measures of nicotine dependence (higher F&V, lower dependence on nicotine). Nicotine dependence is further associated with depression.

These longitudinal findings and nicotine dependence associations may explain the cross-sectional findings. There might be fewer smokers with high F&V intake if depressive symptoms are being removed as an impediment to cessation. The low threshold also suggests that only a small change may be needed to facilitate smoking cessation with F&Vs, warranting further experimental research to test these hypotheses. The most clear and tangible explanation for our findings exist in the neurobiology of food intake, drug use, mood, and mental health.

Neurobiology behind the F&V, depression, and smoking association

Both smoking and consumption of sweet tasting foods such as fruit promote dopamine release and feelings of pleasure or positive affect and reduce negative affect, promoting or inhibiting 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 such as vitamin C 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 F&V and smoking have been found to be monoamine oxidase inhibitors, which increase levels of dopamine and serotonin by inhibiting the action of monoamine oxidase. Higher F&V intake could be hypothesized to act as an alternative MAO inhibitor to smoking, thereby attenuating or possibly eliminating the smokingdepression association. The references and mechanisms described in this paragraph are presented and discussed in further detail in the publication this article is based on.

Conclusions and recommendations

Given our findings in the context of the underlying neurobiology, high F&V consumption may reduce the influence of depression or depressive symptoms, which impede smoking cessation. The neurobiological mechanisms collectively suggest that smokers with higher F&V intake may be less likely to reach for a cigarette for reasons of greater positive affect and lower negative affect. A best next step in research would be to conduct an experimental study to test whether increasing F&V intake might help smokers quit. This would be especially relevant among a sample of persons with a history of depression or intense withdrawal symptoms. Given the various health benefits of F&V, we further recommend that smokers increase F&V intake themselves at healthy levels to see if it helps to improve mood and makes it easier for them to quit, in consultation with their doctor or dietician as appropriate. For example, reach for fruit or vegetables instead of cigarettes and eat fruit or vegetables at every meal. In considering these associations between F&V, depression, and smoking as well as the underlying neurobiology, similar protective associations may exist among F&V and other mental illnesses and addictions.

Based on: Haibach JP, Homish GG, Collins RL, Ambrosone CB, Giovino GA. Fruit and vegetable consumption as a moderator of the association between depressive symptoms and cigarette smoking. Substance Abuse. 2016;37(4):571-578.

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