Using the factor analysis method, four major dietary patterns were identified (Table 1). The first pattern accounted for 19.35% of the variance, loaded positively for tubers, spices, vegetables, salt, oil, eggs and legumes, labeled tubers, and spices. The second pattern (named cereals and dairies), accounted for 13.25% of the total variance, which was characterized by a high intake of cereals and dairy products. Considering the positive load of nut and dry fruits and fruits on the third dietary pattern, this pattern labeled healthy patterns. This pattern accounted for 12.53% of the total variance. Finally, the last extracted pattern accounted for 1.33% of the variance, was characterized by high consumption of high energy drinks, processed foods and snacks, and desserts, and labeled “Western-style” dietary pattern. Totally, these patterns explained 55.48% of the total variance in dietary patterns.
Table 1
Factor-loading matrix for major dietary patterns
Food groups | Tuber and spices | Cereals and dairies | Healthy | Western-style |
Tuber | 0.69 | - | - | - |
Spices | 0.66 | - | - | - |
Vegetables | 0.65 | - | - | - |
Oil | 0.63 | - | - | - |
salt | 0.57 | - | - | - |
Egg | 0.55 | - | - | - |
Legumes | 0.47 | - | - | - |
cereals | - | 0.96 | - | - |
Dairy products | - | 0.96 | - | - |
Nuts and dry fruits | - | - | 0.77 | - |
fruits | - | - | 0.56 | - |
High energy drinks | - | - | - | 0.76 |
Processed meats | - | - | - | 0.58 |
Snacks and desserts | - | - | - | 0.38 |
The demographic characteristics of the two series (cases and controls) were presented in Table 2. There were significant differences between the two groups in the case of age, sex, BMI, smoking status, and self-reported history of H.Pylori infection.
Table 2
Characteristics of participants in case and control groups
Variables | Gastric cancer patients (n = 192) | Healthy controls (n = 365) | p-value* |
Age (years) | 59.87 ± 15.24 | 55.13 ± 15.24 | 0.001 |
Sex (males/females) | 131/61 | 193/172 | 0.001 |
Education n (%) | | | 0.04 |
Illiterate/reading and writing | 119 (61.97) | 193 (52.87) |
≤High school diploma | 57 (29.68) | 132 (36.16) |
≥ college degree | 16 (8.33) | 39 (10.68) |
Marital status | | | 0.01 |
Single | 9 (4.68) | 39 (10.68) |
Married | 165 (85.93) | 292 (80) |
Divorced/widow | 18 (9.37) | 34 (9.31) |
Weight (kg) | 64.45 ± 19.09 | 67.62 ± 17.82 | 0.06 |
BMI (kg/m2) | 23.08 ± 6.72 | 25.36 ± 5.34 | < 0.001 |
Waist circumference | 71.47 ± 36.51 | 73.29 ± 44.37 | 0.62 |
Current smoker n (%) | 69 (35.93) | 64 (17.53) | 0.001 |
Current alcohol consumption | 10 (5.20) | 13 (3.56) | 0.20 |
History of H.pylori infection (yes) | 5 (2.60) | 28 (7.67) | 0.01 |
Number of meals/day | | | |
3 meals | 129 | 253 | 0.65 |
4 meals | 49 | 86 |
≥ 5 meals | 14 | 26 |
Drinking hot tea and eating hot food habit yes (%) | 155 | 110 | 0.005 |
BMI: body mass index |
*chi-square test for comparison between categorical variables, independent test for comparison between continuous variables |
The association between dietary pattern and gastric cancer is shown in table 3. After adjusting for age, education, marital status, BMI, smoking status, hot tea drinking, and hot food eating habits and history of H.Pylori infection, males and females in the highest tertiles of “tubers and spices” dietary pattern tended to have 11.42 (4.17, 26.75) and 6.94 (2.24, 21.56) fold higher odds for gastric cancer risk. “Tubers and spices” dietary pattern loaded positively with tubers, spices, vegetables, salt, oils, egg, and legumes. Previous studies showed a positive association between tubers and spices consumption and the risk of gastric cancer 9. Tubers are rich in starch and nitrite that had been shown as possible risks of gastric cancers. Although there is an inconsistency regarding the association of the nitrite and gastric cancer, a recent meta-analysis study showed that there is a significant positive association between nitrite and gastric cancer risk 15. Spices were the next food group that has significantly loaded on this dietary pattern. A recent meta-analysis confirmed the significant unfavorable effect of high consumption of spices on gastric cancer 16. Previous animal studies also showed the carcinogenetic effect of some spices such as chili extract. In addition, human studies showed that high‑level consumption of capsaicin‑containing foods was associated with an increased risk of cancer 16. Another food that showed significant loading on this dietary pattern was salt. Salt has been considered as an important risk factor of gastric cancer. The effect of high consumption of salt and salty food on gastric cancer risk can be attributed to its direct effect on gastric mucus and its synergic effect with H.Pylori. Epidemiological studies showed a significant association between salt consumption and H.Pylori infection rate 17. Another food group that showed high loading on this pattern was vegetables. Although some previous studies showed the protective effect of vegetables in gastric cancer, a recent meta-analysis in East Asian countries could not show this protective effect 18. Moreover, according to previous studies conducted in Iran, the nitrite content of the vegetables consumed in Iran is higher than the recommended amount of WHO 19. So, this may additionally justify the observed positive association between this dietary pattern and gastric cancer risk.
The result of the present study showed that in the case of “Western-style” dietary pattern, the risk of gastric cancer is significantly higher in individuals in the highest tertile of this dietary pattern (males: 1.16 (1.00-4.35); females: 2.25 (1.10, 6.49)). In contrast, a “healthy” dietary pattern and “cereals and dairies” dietary pattern was not significantly associated with gastric cancer risk neither in males nor females (P > 0.05). This result is consistent with the results of a recent meta-analysis in this regard. In the present study, this pattern was characterized by high consumption of processed meat, high energy drinks, and desserts. It is postulated that these food groups had an unfavorable effect on gastric cancer through increasing overweight and obesity 20.
There was not a significant association between “cereals and dairies” dietary patterns and gastric cancer risk. In the present study, this dietary pattern was characterized by high consumption of cereals and dairy products. Cereals are rich in starch. Previously it has been shown that starchy foods increase the risk of gastric cancer 21. On the other hand, in earlier studies, the protective effect of dairy products on gastric cancer risk had been demonstrated 22. So, the absence of an association between this dietary pattern and gastric cancer risk could be attributed to the counteraction effect of these food groups on gastric cancer.
Table 3
Odds ratio of gastric cancer risk by tertiles of dietary patterns.
|
Males
|
Females
|
Total
|
Tubers and spices
|
OR*
|
95%CI
|
OR*
|
95%CI
|
OR*
|
95%CI
|
T 1
|
1
|
-
|
1
|
-
|
1
|
-
|
T 2
|
3.51
|
1.53-7.96
|
1.97
|
0.61-6.22
|
3.25
|
1.71-6.16
|
T 3
|
11.42
|
4.87-26.75
|
6.94
|
2.24-21.56
|
9.95
|
5.25-18.53
|
p-value for trend
|
|
<0.001
|
|
0.001
|
|
<0.001
|
|
Cereals and dairy products
|
|
|
|
|
|
T 1
|
1
|
-
|
1
|
-
|
1
|
-
|
T 2
|
0.99
|
0.48-2.07
|
0.62
|
0.24-1.55
|
0.84
|
0.49-1.45
|
T 3
|
1.30
|
0.60-2.82
|
0.26
|
0.08-1.00
|
0.79
|
0.44-1.44
|
p-value for trend
|
0.29
|
|
0.1
|
|
0.91
|
|
Healthy dietary pattern
|
|
|
|
|
|
T 1
|
1
|
-
|
1
|
-
|
1
|
-
|
T 2
|
1.08
|
0.54-2.17
|
1.27
|
0.60-4.32
|
1.18
|
0.67-2.08
|
T 3
|
1.71
|
0.83-3.50
|
1.93
|
0.90-6.99
|
1.77
|
1.00-3.16
|
p-value for trend
|
0.13
|
|
0.07
|
|
0.05
|
|
Western-style dietary pattern
|
|
|
|
|
|
T 1
|
1
|
-
|
1
|
-
|
1
|
-
|
T 2
|
1.60
|
0.73-3.29
|
3.87
|
1.70-12.52
|
2.36
|
1.25-4.15
|
T 3
|
2.06
|
1.00-4.23
|
2.85
|
1.10-6.49
|
2.63
|
1.39-4.49
|
p-value for trend
|
0.04
|
|
0.003
|
|
<0.001
|
|
OR: Odds ratio; 95%CI: 95% confidence interval; T: tertile, T1: lowest compliance to dietary pattern, T#: highest compliance to dietary pattern
Adjusted for age, education, marital status, BMI, smoking status, history of H.pylori infection, habit of drinking hot tea or eating hot food
Limitations
In the present study, we used a factor analysis approach. Different steps used in this method are subjective. Moreover, qualitative FFQ was used in the dietary pattern approach. The limitations of this questionnaire also apply to the dietary pattern approach. Moreover, due to using qualitative FFQ, it could not be possible to control the results for energy intake. Additionally, the hospital-based design of the study could be considered as another limitation of the study. Moreover, we did not match controls individually with cases but in the regression analysis, the results were controlled for a large number of potential confounders such as age, dietary behaviors (the number of meals and hot tea drinking, or hot food eating habit), and anthropometric measurements.