Impact of Interactions Between Self-Reported Psychological Stress and Habitual Exercise on the Dietary Intake of Japanese Men and Women : a Large-Scale Cross-Sectional Study

In 2012, cancer was the leading cause of death in the world; 8.2 million people died from cancer worldwide (World Health Organization, 2015). It is estimated that 30% of deaths from cancer are associated with adult obesity and diet and 5% with a sedentary lifestyle (Harvard Center for Cancer Prevention, 1996). Furthermore, studies have found that vegetables and their related vitamins reduce the risk of various types of cancer (World Cancer Research Fund American Institute for Cancer Research, 2007). Convincing evidence exists showing that exercise decreases the risk of colon cancer, and some evidence exists suggesting that exercise decreases the risk of breast and endometrial cancer as well (World Cancer Research Fund American Institute for Cancer Research, 2007). In Japan, cancer has been the leading cause of death since 1981. To decrease deaths from cancer, the Ministry of Labour and Welfare in Japan announced a new plan for


Introduction
In 2012, cancer was the leading cause of death in the world; 8.2 million people died from cancer worldwide (World Health Organization, 2015).It is estimated that 30% of deaths from cancer are associated with adult obesity and diet and 5% with a sedentary lifestyle (Harvard Center for Cancer Prevention, 1996).Furthermore, studies have found that vegetables and their related vitamins reduce the risk of various types of cancer (World Cancer Research Fund American Institute for Cancer Research, 2007).Convincing evidence exists showing that exercise decreases the risk of colon cancer, and some evidence exists suggesting that exercise decreases the risk of breast and endometrial cancer as well (World Cancer Research Fund American Institute for Cancer Research, 2007).In Japan, cancer has been the leading cause of death since food intake were observed across the three levels of SRPS for participants with an unhealthy lifestyle (chi-squared test; p<0.001 for men and women).However, few studies habitual exercise, and dietary intake of food and nutrients.
In the present study, we investigated the interaction between self-reported PS (SRPS) and habitual exercise on the dietary intake of various foods and nutrients in Japanese men and women.

Subjects
From July 2005 to March 2007, we recruited individuals who attended a health checkup at a local health center in Shizuoka, Japan (Mochizuki et al., 2011;Endoh et al., 2015a;Endoh et al., 2015b).An in-person explanation was provided and written informed consent for participation in the study was obtained from 12,066 subjects.Of these, 3,761 (31.2%) met the following exclusion criteria: (1) less than 29 or greater than 79 years of age (n=84, 0.7%), (2) missing value for SRPS (n=663, 5.5%), (3) 61 years of age or greater (n=2,373, 19.7%), excluded because most were retired and had no job-related stress, (4) past or present history of depression or being treated with an anti-depressant or tranquilizer (n=189, 1.6%), (5) energy intake (n=793, 6.6%) and body mass index (BMI) (n=761, 6.3%) greater or less than 2 standard deviations from the mean, (6) missing data for lifestyle factors (n=489, 4.1%), ( 7) extremely short or long sleep times (n=246, 2.0%), and (8) past or present disease history of stroke, myocardial infarction, or cancer (n=442, 3.7%).Ultimately, 5,587 (46.3%) men and 2,718 (22.5%) women were included in the analysis.This study was conducted according to the Declaration of Helsinki and all procedures involving human subjects were approved by the Ethics Committee of the University of Shizuoka.

Lifestyle assessment
Anthropometric measurements such as height, weight, and blood pressure were taken by trained staff at a local health center.Blood was taken after an overnight fast, and HbA1c, total cholesterol, high-density lipoprotein cholesterol, and triglycerides were measured.Information on age, smoking status (never, past, or current), sleeping time (hours per day), SRPS, and present and past disease history was obtained by trained medical staff.To calculate BMI, weight (kg) was divided by height (m) squared (kg/ m 2 ).To determine SRPS, we asked each participant "Do you feel stress?".The four possible answers (no, little, (n=206 responded "no" and n= 1,993 "little"), moderate (n=4,938 responded "moderate") and high (n=1,168 responded "extreme").To assess habitual exercise, the subjects were asked "Do you exercise regularly?"and answered either yes or no.The subjects who answered yes were considered exercisers and those who answered no were non-exercisers.A scientifically validated food frequency questionnaire (Kobayashi et al., 2011;Kobayashi et al., 2012) was used.This questionnaire contains 58 food items and foods, which were used to calculate the intake of energy and 42 nutrients.The dietary intake of each food and nutrient was calculated and adjusted for energy intake.

Statistical analyses
The adjusted means for the dietary intake of food and nutrients were calculated by stratifying participants by the presence or absence of habitual exercise (i.e., the exerciser and non-exerciser groups).A general linear between SRPS levels and habitual exercise on the dietary intake of food and nutrients.The model was adjusted for the following confounding variables, as in our previous studies (Endoh et al., 2015a;Endoh et al., 2015b): age (years), BMI (kg/m 2 ), dietary energy (kcal/day), alcohol intake (g/day), sleeping time (hours/day), smoking status (never, past, or current smoker), and past or present history of hypertension and diabetes mellitus (yes or no).All reported p values were based on two-sided tests.Statistical analyses were conducted using PASW Statistics 18 (SPSS

Results
Table 1 shows the demographic characteristics of the subjects.The mean BMI and percentages of participants who drink and smoke were higher in men.The proportions of participants with each SRPS level and who exercise  were approximately equal between men and women.
Regarding the dietary intake of nutrients, Table 3 habitual exercise levels among middle-aged Japanese men and women.In male non-exercisers, SRPS was positively associated with the dietary intake of saturated fatty acids and negatively associated with the dietary intake of copper.
In male exercisers, SRPS was negatively associated with interactions were found between SRPS levels and habitual exercise in the dietary intake of any nutrients.In female non-exercisers, SRPS was positively associated with vitamin B2.In female exercisers, SRPS was negatively associated with protein, animal protein, vitamins E, B1, B6, and C, potassium, magnesium, phosphorus, iron, and interactions were found between SRPS levels and habitual exercise in the intake of vegetable protein, soluble, carotene, retinol equivalent, vitamin B2, pantothenic acid, potassium, calcium, magnesium, phosphorus, and iron (p for interaction <0.05 for all).

Discussion
between SRPS levels and habitual exercise on the dietary intake of "pork and beef", "low fat milk and yogurt", natto (fermented soybean), "carrot and squash", other root vegetables (onions, burdock, and lotus root), mushrooms, seaweeds, wine, vegetable protein, soluble, insoluble, and equivalent, vitamin B2, pantothenic acid, potassium, calcium, magnesium, phosphorus, and iron in women.levels and habitual exercise on the dietary intake of "raw vegetables used in salad (cabbage and lettuce)", green leafy vegetables, and "fruit juice and vegetable juice".
was observed between SRPS and habitual exercise on in women.This suggests that both SRPS and habitual exercise are possible factors that mediate the dietary intake of food and nutrients in women.It also implies that studies of the dietary intake of food and nutrients should analyze SRPS and habitual exercise concurrently.Consumption of vegetables and fruits and the related nutrients decreases the risk of cancer (World Cancer Research Fund American Institute for Cancer Research, 2007).If both PS and habitual exercise change the dietary intake of vegetables, fruits, and the related vitamins and minerals, the risk of cancer might be modulated by both PS and habitual between PS and habitual exercise on the dietary intake of food and nutrients.Our study results are useful for investigating the association between diet and cancer risk.
Further studies using a prospective design are warranted, as our study was conducted using a cross-sectional design.
In the present study, interactions between SRPS and habitual exercise on the dietary intake of 8 foods and 15 nutrients were found in women.However, interactions between SRPS and habitual exercise were found in the dietary intake of only 3 foods in men.These gender differences could be explained by several factors.The sensitivity to PS differs between men and women (Young and Korszun, 2010).Overall, men are more physically active (Zitouni and Guinhouya, 2012;Peer et al., 2013).The dietary intake of food and nutrients differs among men and women (Iso et al., 2005).Therefore, gender differences in PS, exercise, and diet might be some of the reasons that different results were observed in men and women in the present study.Further studies of other Perimenopausal women may have physical symptoms, such as hot flashes and tachycardia, and psychological manifestations, such as depression (Soares, 2013).Genistein, one of the isoflavones, improved depressive symptoms (Atteritano et al., 2014).In the and habitual exercise on the dietary intake of genistein, daidzein, and natto (fermented soy bean) were found in women.Our results imply that both SRPS and habitual soy bean products by perimenopausal women should be examined in the context of PS and habitual exercise.However, further studies are needed because this study was conducted using a cross-sectional design.
This study has several limitations.First, we did not determine the type, intensity, frequency, and duration of habitual exercise.However, in a large-scale study, physical activity levels assessed using a single item question could be used to properly classify the subjects (Sternfeld et al., 2000).Second, PS was assessed by self-report.An unhealthy lifestyle, including physical inactivity, drinking, smoking, and being overweight, is associated with PS (Heikkila et al., 2013).Previously, we drinking (Endoh et al., 2015b).Therefore, we believe that our SRPS accurately measures PS.Third, the cause and effect relationship across PS, habitual exercise, and diet was not elucidated because of the study design.Fourth, PS is associated with socioeconomic status (Lorant et al., 2003) but we did not collect this information from the study subjects.
We demonstrated a synergic effect of SRPS and habitual exercise on the dietary intake of food and nutrients related to vegetables which a have protective effect against cancer, especially in women.Our study results are useful for cancer research.Further studies are needed to better understand the role of PS, exercise, and dietary intake in cancer prevention.

Table 3 (continued). Interactions between SRPS and Habitual Exercise Level in the Dietary Intake of Energy and Food Types in Middle-aged Japanese men and Women 1
DOI:http://dx.doi.org/10.7314/APJCP.2016.17.4.2007Impact of Interaction of Psychological Stress with Habitual Exercise on Dietary Intake

Table 3 (continued). Interactions between SRPS and Habitual Exercise Level in the Dietary Intake of Energy and Food Types in Middle-aged Japanese men and Women 1
Multi-adjusted linear regression analyses were adjusted for age, body mass index, exercise, smoking, energy, alcohol intake, history of disease (hypertension and diabetes mellitus) and sleeping time.Drinking, exercise and history of disease were assumed to be dichotomous variables (non-drinker, non-exercisers or no history of hypertension or diabetes mellitus=0; drinker, habitual exercisers or having a history of hypertension or diabetes mellitus=1).SRPS levels and smoking were assumed to be a trichotomous variable (low or never=0; moderate or past=1; high or current=2).Dietary intake of 58 food items was estimated from a food frequency questionnaire; 2 Values are shown as the adjusted means (standard error); 3 Non-exercisers (men=2,918 ; women=1,485); 4 Exercisers (men= 2,669; women=1,233); akcal/day, bug/1,000kcal exercise.Elucidating the possible factors that change the dietary intake of food and nutrients is important for cancer prevention, because approximately 30% of cancer cases are linked to diet (Harvard Center for Cancer Prevention,