Dietary Phytochemical Index and Risk of Gallstone Disease: A Case‐Control Study

ABSTRACT

Background and Aims

Gallstone disease (GSD), a common gastrointestinal disorder, arises from a combination of genetic and metabolic factors. Its rising prevalence is strongly linked to obesity, insulin resistance, and dyslipidemia, all of which are modifiable through dietary interventions. The dietary phytochemical index (DPI), representing the consumption of bioactive plant‐based compounds, may influence GSD risk. This study explored the association between DPI and GSD risk.

Methods

This case‐control study was conducted on 189 newly diagnosed GSD patients and 342 controls. Dietary intake data were collected using a validated 168‐item food frequency questionnaire and DPI was calculated as follow: daily energy obtained from foods rich in phytochemicals (kcal)/total daily energy intake (kcal)) × 100. Phytochemical‐rich foods include whole grains, fruits, vegetables, olive oil, legumes, nuts, and seeds. Logistic regression models were applied to compute odds ratios (ORs) and 95% confidence intervals (CIs), adjusting for potential confounders.

Results

A significant reduction in GSD cases was observed with increasing DPI scores (p < 0.001). Higher DPI scores were significantly associated with lower risk of GSD in crude and adjusted models (OR _{T3 vs. T1} = 0.30, 95% CI: 0.19–0.52, P for trend < 0.001).

Conclusion

These findings demonstrated a significant inverse association between DPI and the risk of gallstone disease, indicating that phytochemical‐rich foods may be protective against gallstone formation.

Summary

• Phytochemical‐rich foods include whole grains, fruits, vegetables, olive oil, legumes, nuts, and seeds.

• Higher dietary phytochemical scores were significantly associated with lower risk of gallstone.

• Phytochemical‐rich foods may be protective against gallstone formation.

• It is logical to replace energy‐dense nutrient‐poor foods with phytochemical‐rich dietary components.

1. Introduction

Gallstone disease (GSD) is among the most common gastrointestinal disorders [1]. GSD prevalence ranges from 10% to 20% among adult population [2]. A study conducted in Iran reported that the prevalence of GSD was 6.3% [3]. It has been reported that the United States has experienced a nearly twofold increase in GSD cases over the past three decades, likely driven by a rise in metabolic disorders such as prediabetes and diabetes, obesity and metabolic syndrome which are key risk factors [4]. Multiple metabolic abnormalities including obesity, dyslipidemia, insulin resistance, and disruptions in cholesterol homeostasis, have been closely linked to gallstone formation [2]. Gallstone formation is influenced by several key factors, including genetic predisposition, excessive liver cholesterol secretion leading to bile supersaturation, impaired gallbladder motility, and specific intestinal diseases [5]. Gallstone can lead to serious complications such as acute cholecystitis, obstructive cholangitis, and gallstone pancreatitis, which often require hospitalization and put a significant burden on the healthcare system [6].

Inflammation seems to be a crucial factor in the pathogenesis of gallstones. Chronic inflammation of the gallbladder can alter bile composition and impair gallbladder motility, contributing to the formation of gallstones. Tumor necrosis factor alpha (TNF‐α) is an inflammatory factor that can stimulate the accumulation of cholesterol in the gallbladder, ultimately resulting in the formation of gallstones [7]. Similarly, a direct association between certain circulating interleukins and the risk of GSD has been indicated [8]. Also, obesity, as a risk factor for GSD, is an inflammation‐related condition [9]. It has been shown that a higher dietary inflammatory index (DII) and elevated serum inflammatory and oxidative stress biomarkers were associated with an increasing risk of GSD in Iranian women [10].

Dietary modification may be beneficial adjuvant approaches to reducing GSD risk [4, 11], as the anti‐inflammatory potential of specific foods and dietary patterns may influence GSD [10]. Phytochemicals are bioactive dietary compounds derived from plants which are classified into seven main categories: phenolic compounds, terpenes, betalains, organosulfides, indoles/glucosinolates/sulfur compounds, protein inhibitors, and other organic acids [12]. McCarty introduced the phytochemical index (PI) to evaluate the beneficial effects of phytochemicals on various diseases in epidemiological studies [13]. Studies have shown that a combination of various phytochemicals found in a wide range of foods such as fruits, vegetables, whole grains, nuts, and cocoa/chocolate, as well as beverages like fruit juices, tea, coffee, and wine, may have potential anti‐inflammatory effects [12]. Dietary phytochemicals can also reduce the risk of GSD by improving lipid metabolism [14]. Also, higher intakes of dietary fiber, a source of polyphenols, were significantly linked to a reduced risk of GSD [15]. A meta‐analysis indicated that dietary polyphenols may help prevent and manage obesity, a risk factor for GSD [16].

However, evidence linking the Dietary Phytochemicals Index (DPI) specifically to gallstone risk is inadequate. With the rising prevalence of GSD, along with related conditions such as obesity, prediabetes, and pro‐inflammatory dietary patterns, dietary intervention should be considered as a crucial approach to mitigate this risk. Our study aims to determine the association between DPI and the risk of GSD.

2. Materials and Methods

2.1. Study Design and Population

Details of the study design was presented in another published study from the same project [15]. In summary, 189 newly patients diagnosed with GSD and 342 controls were enrolled in the study. Eligible participants consisted of adults, both sexes, who were willing to participate in the study. Demographic information and anthropometric measurements of all patients were recorded. The study protocol was approved by the Research Institute of Gastroenterology and Liver Diseases Ethics Committee, Shahid Beheshti University of Medical Sciences (IR.SBMU.RIGLD.REC.1396.159). Informed written consents were obtained from all participants.

2.2. Calculation of the Dietary Phytochemical Index

The dietary intake was assessed using a 168‐item food frequency questionnaire (FFQ) [17]. The portion sizes of various food items consumed in households were first described, followed by recording the frequency of their consumption over the past year on a monthly, weekly, and daily basis. This data was then converted into grams. Calculations were carried out using Nutritionist IV software and the Iranian and US Department of Agriculture Food Composition Table to analyze nutrient and energy content. Using the information obtained from the dietary data analysis, DPI was calculated based on the method introduced by McCarty, according to the following formula [13]:

$$\mathit{DPI}=\left(\frac{\text{daily energy intake from foods rich in phytochemicals}\left(\text{kcal}\right)}{\text{total daily energy intake}\left(\text{kcal}\right)}\right)\mathrm{\times }100$$

Fruits, vegetables (including natural whole fruit and vegetable juices), legumes, whole grains, nuts, soy products, seeds, and olive oil were considered phytochemical‐rich foods.

2.3. Statistical Analysis

Statistical analyses were performed using statistical package for the social sciences software, version 19.0 (SPSS Inc., Chicago, IL, USA). The normality of continuous variables was assessed using the Kolmogorov‐Smirnov test and histogram. Baseline characteristics and dietary intake data were presented as means ± standard deviation (SD) for continuous variables and as frequencies (percentages) for categorical variables. Participants were categorized into tertiles based on DPI. One‐way analysis of variance (ANOVA) and χ2 test were used for quantitative and qualitative variables, respectively. Crude and multivariable‐adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using multiple logistic regression models for GSD risk associated with tertiles of DPI. Model 1 was considered unadjusted and confounders were included in a subsequent order, as follows: Model 2 was adjusted for age and sex, Model 3 was further adjusted for energy intake, body mass index (BMI), physical activity, smoking (at least one cigarette a day), and using alcohol (intake of > 20 g/d). A two‐tailed p‐value of 0.05 was used to define statistically significant results.

3. Results

In another paper from the same project, a comparison of initial characteristics between cases and controls is reported [15]. In total, 531 patients including 189 cases and 342 controls (197 men and 334 women) were analyzed. Table 1 summarizes the characteristics of participants and their dietary intakes according to tertiles of DPI. As the DPI score increased, the number of individuals with GSD decreased significantly. However, no significant differences were observed between DPI tertiles in terms of demographic, physical activity, and anthropometric parameters. Among the food groups, intake of fruits, vegetables, and legumes, seeds and nuts showed significant differences. Table 2 presents ORs and 95% CIs for the risk of GSD across DPI tertiles. An inverse significant association between DPI intake and the risk of GSD was found. In the unadjusted model, the odds were 61% lower, and in the adjusted models, they were 68% and 70% lower, respectively, of GSD (p for trend < 0.001).

Table 1.

Characteristics of participants according to the tertile of DPI.

	Tertile of total DPI
	T1 (n = 177)	T2 (n = 177)	T3 (n = 177)	p value
Cases, n (%)	94 (53)	55 (31)	40 (22)	< 0.001
Sex (male n, %)	58 (32)	59 (33)	62 (35)	0.50
Age (y)	52.2 ± 14	51.4 ± 12.6	55.3 ± 12.8	0.11
IPAQ level, n, %				0.13
1	145 (82)	126 (71)	129 (73)
2	27 (15)	46 (25)	43 (24)
3	5 (3)	8 (4)	5 (3)
Alcohol drinker, (%)	4 (2.3)	5 (2.9)	4 (2.3)	0.92
Smoker, (%)	24 (13.6)	26 (14.9)	27 (15.3)	0.90
Weight, kg	73.5 ± 14.1	73.2 ± 13.1	72.8 ± 13	0.90
Height, cm	164.3 ± 9.1	165 ± 8.4	164.7 ± 8.6	0.76
Body mass index, kg/m2	27.2 ± 4.8	26.8 ± 4	26.8 ± 4.1	0.58
Calorie intake (Kcal/day)	2583 ± 650	2357 ± 625	2156 ±‌ 506	< 0.001
Fruits	250 ± 147	347 ± 190	433 ± 212	< 0.001
Vegetables	246 ± 141	324 ± 167	388 ± 194	< 0.001
Legumes, nuts and seeds	34 ± 23	63 ± 41	81 ± 43	< 0.001
Cereals	363 ± 166	364 ± 155	328 ± 152	0.06
Dairy	276 ± 199	279 ± 164	291 ± 172	0.70
Meats	89 ± 47	94 ± 43	97 ± 44	0.26

Note: Values are means ± SDs for continuous variables and percentages for categorical variables. ANOVA for quantitative variables and χ² test for qualitative variables. Threshold for statistical significance was p‐value < 0.05.

Table 2.

Odds and 95% confidence interval for occurrence of the gallstone in each tertile of DPI.

	Tertiles
	T1	T2	T3
DPI	(< 17)	(17–27)	(27 ≤)	P trend
No. of cases	94	55	40	< 0.001
Model 1	Ref	0.26	0.39	< 0.001
		(0.16–0.41)	(0.25–0.59)
Model 2	Ref	0.24	0.32	< 0.001
		(0.15–0.39)	(0.2–0.5)
Model 3	Ref	0.25	0.30	< 0.001
		(0.15–0.42)	(0.19–0.52)

Note: Based on multiple logistic regression model.

Model 1: crude

Model 2: adjusted for age and sex

Model 3: additionally adjusted for energy intake, BMI, physical activity, smoking, alcohol

Threshold for statistical significance was p‐value < 0.05.

4. Discussion

The findings of present case‐control study provided evidence for a significant inverse relationship between the DPI and the risk of GSD. The results showed that compared to the reference tertile, the highest DPI score was associated with a 70% reduction in disease risk. These results are consistent with previous research suggesting that diets rich in phytochemicals, such as fruits, vegetables, and legumes, may have a protective role against gallstone formation [15, 18].

A recently published study by Jebur et al. is consistent with the findings of the present study, showing that a higher DPI score is associated with a 50% reduction in the risk of GSD [19]. Existing evidence suggests improved health outcomes with increased DPI, and an inverse association has been shown between DPI and the risk of chronic diseases such as obesity, insulin resistance, oxidative stress, and hypertriglyceridemia [20, 21, 22]. Existing literature suggests that GSD and associated metabolic risk factors such as diabetes and insulin resistance, obesity, and lipid abnormalities stem, in part, from inflammation [2, 4]. Circulating inflammatory biomarkers including interleukins – IL‐6, IL‐10, IL‐12 and IL‐13 – have also been reported to be significantly associated with a higher likelihood of GSD [8]. Similarly, in another study, increased hs‐CRP concentration has been introduced as an independent risk factor for new onset GSD in the Chinese population [23]. Therefore, studies have investigated the relationship between diet‐induced inflammation and GSD, with results supporting this hypothesis [24, 25]. Anti‐inflammatory diets rich in antioxidants appear to reduce the incidence of GSD in adults [26]. Also, an inverse association between DPI and inflammatory levels has been shown in epidemiological studies and clinical trials, highlighting the anti‐inflammatory benefits of plant‐based diets rich in phytochemicals [27, 28].

Dietary phytochemicals, including polyphenols, flavonoids, and carotenoids, have been shown to reduce high‐sensitivity C‐reactive protein (hs‐CRP) levels due to their antioxidant and anti‐inflammatory properties. Phytochemicals reduce inflammation and improve overall health through multiple mechanisms [25]. Polyphenols protect cells from inflammation and oxidative stress by inhibiting pro‐inflammatory enzymes such as cyclooxygenase‐2 (COX‐2) and activating the nuclear factor erythroid 2–related factor 2 (Nrf2) pathway. Flavonoids neutralize reactive oxygen species (ROS) and bind metal ions, which enhances their antioxidant effects. Carotenoids also scavenge free radicals and reduce the production of hs‐CRP. Lutein specifically inhibits inflammatory pathways involving hs‐CRP. Dietary polyphenols, like apigenin and luteolin, also exhibit anti‐inflammatory and antiangiogenic effects by blocking the IL‐6/STAT3 pathway. They reduce the activity of JAK/STAT3 and mitogen‐activated protein kinase (MAPK), which activate IL‐6, leading to less migration and growth of endothelial cells. These polyphenols also lower IL‐6 receptor levels and reduce the secretion of enzymes like matrix metalloproteinase‐2 (MMP‐2). They suppress IL‐6 signaling, helping to reduce inflammation and prevent angiogenesis [29]. Additionally, dietary phytochemicals improve lipid metabolism through different mechanisms, including inhibition of endogenous lipid biosynthesis, enhancement of exogenous lipid metabolism, regulation of lipid redistribution, transportation, excretion, and reduction of lipid peroxidations [29]. In a cross‐sectional study, an inverse association was found between adherence to a diet with a high phytochemical index and the likelihood of central obesity, especially in women [30]. In addition, recent systematic results suggest that a high phytochemical index diet is associated with lower weight, waist circumference, and triglycerides, and a reduced risk of metabolic syndrome. Dietary phytochemicals help reduce insulin resistance and improve fat metabolism, which are associated with GSD [31]. Disorders in lipid metabolism, particularly decreased HDL and increased triglycerides, are known to increase the risk of GSD [32].

Caution should be exercised when interpreting the present study. Limitations of the study include the lack of follow‐up of patients and the failure to draw definitive conclusions about the causal relationship between DPI and GSD. Furthermore, the information collected on dietary intake was based on self‐reports, and recall bias is inevitable in the FFQ. Information on education, socioeconomic status, and other demographic characteristics of the patients was also not assessed. The study also had some strengths. Based on the existing literature, few studies have examined the association between DPI and GSD risk with such a comprehensive approach. Recently diagnosed participants reduced recall bias. In addition, conducting all interviews by a same skilled interviewer reduced the risk of interviewer bias.

5. Conclusions

The present study provides further evidence to the protective role of diets rich in phytochemicals in GSD. The inverse association between DPI and GSD should be considered when providing dietary recommendations to GSD patients and the general population. According to the findings of this study, it is advisable to replace energy‐dense nutrient‐poor foods with phytochemical‐rich dietary components. However, without further and larger studies, it is not possible to draw definitive conclusions about the relationship between DPI and GSD risk.

Author Contributions

Zeinab Ghaeminejad: project administration, writing – original draft. Leyli Zahra Bahreini Boroujeni: writing – original draft, project administration. Fatemeh Javaheri‐Tafti: writing – original draft, project administration. Seyed Ali Abbas‐Hashemi: writing – original draft, methodology. Azita Hekmatdoost: conceptualization, writing – review and editing. Moloud Ghorbani: methodology. Amir Sadeghi: methodology. Zahra Yari: conceptualization, formal analysis, writing – original draft, writing – review and editing.

Ethics Statement

The study protocol was approved by the Research Institute of Gastroenterology and Liver Diseases Ethics Committee, Shahid Beheshti University of Medical Sciences (IR.SBMU.RIGLD.REC.1396.159). Informed written consents were obtained from all participants.

Consent

The authors have nothing to report.

Conflicts of Interest

The authors declare no conflicts of interest.

Transparency Statement

The lead author Zahra Yari affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request. The datasets analyzed in the current study are available from the corresponding author on reasonable request.