Abstract
Background
Limited research has been conducted on the effects of dietary fiber (DF) intake on gallstones. We aimed to investigate the actual DF intake in a nationally representative sample in the United States (US) and explore its association with gallstones.
Methods
We used data from the National Health and Nutrition Examination Survey database, including the 2017–2020 and 2021–2023 cycles. Using participants’ gallstone histories and their average 2-day DF intake, we investigated the actual DF intake among US adults. After adjusting for traditional confounders, we used weighted multivariable logistic regression models, trend tests, spline curve fitting, subgroup analyses, and interaction tests to explore the independent association between DF intake and gallstones.
Results
A total of 8,782 participants were included. The weighted analysis showed the prevalence of gallstones is 10.03%. The average DF intake among adult men and women is 18 ± 10 g/day and 15 ± 7.8 g/day, respectively, which is well below the recommended levels. Multivariable regression analysis revealed a statistically significant negative linear association between DF intake and gallstone prevalence. For every 10 g/day increase in DF intake, the risk of gallstones significantly decreases by 21% (OR = 0.79, 95% CI: 0.63-1.00, P = 0.047). Curve fitting showed a negative linear relationship between these two variables (P = 0.003, P for non-linearity = 0.134).
Conclusion
A negative linear relationship between DF intake and gallstones among adults in the US was observed, and the current DF intake in the US is far below recommended levels.
Keywords: Dietary fiber intake, Gallstones, Cross-sectional study, NHANES
Introduction
Gallstone disease is one of the most common digestive disorders, with a global prevalence of approximately 10% [1, 2]. In the United States (US), the prevalence of gallstones ranges from 10% to 20%, with associated annual healthcare costs exceeding 6 billion USD, resulting in a significant economic burden [3–5]. Moreover, with the rising prevalence of related conditions, such as obesity and metabolic syndrome, these figures may be higher [4, 6]. In addition to common benign conditions such as cholecystitis, cholangitis, and pancreatitis, gallstones are associated with cancers (gallbladder and colorectal), cardiovascular diseases, and even death, making them a critical global health issue [2, 7–12]. Therefore, identifying the risk factors for gallstones is essential for developing public health policies to prevent their formation and alleviate the associated disease and economic burden.
Dietary fiber (DF) is an important nutrient found in plant-based foods and refers to the components of plant materials that are indigestible by human endogenous digestive enzymes [13–15]. Although the human body cannot digest it, DF modulates the gut microbiota, increases stool bulk, lowers total cholesterol (TC) and blood lipid levels, aids digestion, controls blood glucose levels, and manages body weight [15–18]. Many studies have suggested that increasing DF intake helps prevent constipation, hemorrhoids, colorectal cancer, metabolic syndrome, cardiovascular diseases, and epilepsy and improves sleep quality [14, 18–21]. A high-calorie, low-fiber diet is considered one of the risk factors for gallstones [22].
However, research on the relationship between DF intake and the risk of gallstones is limited, and the small sample sizes of existing studies are common limitations in exploring this association. Therefore, we extracted data from the National Health and Nutrition Examination Survey (NHANES) to investigate the relationship between DF intake and gallstones in a representative sample of the US population. We hypothesized that individuals with gallstones would have a lower DF intake. The findings were adjusted for known confounding factors, providing additional evidence of the independent effect of DF intake on gallstone risk, thereby offering valuable guidance for personalized dietary recommendations for prevention.
Materials and methods
Data sources
NHANES is a nationwide survey conducted by the National Center for Health Statistics. NHANES aims to assess the health and nutritional status of adults and children in the US. Moreover, this survey uses a scientifically rigorous, complex, multistage probability sampling method to select participants representing the entire US population. Demographic data, dietary information, physical examination data, laboratory test results, and questionnaire responses are collected from the participants. The NHANES releases data every 2 years; however, because of the COVID-19 pandemic, field operations were suspended in March 2020. Consequently, data collection for the 2019–2020 cycle was incomplete, and the collected data did not have national representativeness. Therefore, data gathered from 2019 to March 2020 were combined with data from the 2017–2018 cycle to form a nationally representative pre-pandemic dataset for NHANES 2017–March 2020. All these data are available from the NHANES official website at https://wwwn.cdc.gov/nchs/nhanes/default.aspx.
Study population
Because gallstones were only investigated in 2017–March 2020 and 2021–2023, we extracted data from these NHANES cycles for analysis in this cross-sectional study. Participants with missing data on gallstones, DF intake, and covariates were excluded. Additionally, individuals younger than 20 years and pregnant women were excluded. After the final screening, 8,782 participants were included. Figure 1 illustrates the participant selection process.
Fig. 1.
Flowchart for screening subjects from the NHANES
Exposure variable
In collecting the DF data, the NHANES officially stated that all participants were eligible for two 24-hour dietary recall interviews. The first dietary recall interview was conducted at a Mobile Examination Center, and the second interview was conducted via telephone 3–10 days later. From August 2021 to August 2023, both dietary recall interviews were conducted via telephone to minimize the risk of SARS-CoV-2 exposure. Food energy and the daily totals of 64 nutrients/food components for all foods and beverages were calculated using the Food and Nutrient Database for Dietary Studies released by the US Department of Agriculture for the corresponding years.
We used the average DF intake on the first and second days as the exposure factor for the analysis. Additionally, the participants’ DF intake was categorized into quartiles to further explore its association with gallstones.
Outcome variable
Information on gallstones, the outcome variable, was obtained through interviews conducted by trained interviewers using a computer-assisted personal interview system. Participants reported their gallstone status by answering the question, " Has a doctor or other health professional ever diagnosed you with gallstones?” Participants who answered “yes” were classified as having a history of gallstones, while those who answered “no” were considered to have no history of gallstones. This simple and easily accessible method has been employed in many previous studies [2–5].
Covariables
Based on previous literature [2–5] and clinical judgment, various potential covariates were identified, including age, gender, race/ethnicity, marital status, education level, family income, body mass index (BMI), TC levels, high-density lipoprotein cholesterol (HDL-C), hypertension, diabetes, coronary heart disease (CHD), sedentary activity, smoking, and total dietary intake of energy, carbohydrates, fat, and protein.
Race/ethnicity was categorized as Mexican American, Other Hispanic, Non-Hispanic White, Non-Hispanic Black, and other races. Marital status was classified as married/living with a partner, widowed/divorced/separated, and never married. Education level was divided into below high school, high school, and above high school. According to a report from the US government [23], family income was categorized by the poverty-income ratio (PIR) into three groups: low (PIR ≤ 1.3), medium (1.3 to 3.5), and high (PIR > 3.5). BMI was grouped into three categories using 25 and 30 kg/m2 as the cutoff points. The presence of previous diseases (hypertension, diabetes, and CHD) was determined based on self-reported information from the questionnaire, which asked participants whether they had been previously diagnosed with these conditions. Smoking status was assessed based on the question, “Have you smoked at least 100 cigarettes in life?” Dietary intakes of total energy, carbohydrates, fat, and protein were determined using the same method as for DF intake.,
Statistical methods
To ensure the generalizability of the study findings to the entire US population, we employed complex sampling weighted methods, as recommended by the official NHANES guidelines. For the 2017 to March 2020 data, we used the dietary two-day sample weight (WTDR2DPP) and adjusted it using WTDR2DPP*3.2/5.2. For the 2021 to 2023 data, the dietary two-day sample weight (WTDR2D) was applied and adjusted using WTDR2D*2/5.2.
All normally distributed continuous variables are presented as means ± standard deviation, whereas skewed continuous variables are described using medians and interquartile ranges. Comparisons of continuous variables between groups were conducted using the independent samples Student’s t-test or the Mann–Whitney U test, depending on the normality of the data distribution. Categorical data were analyzed using the chi-square test, as appropriate. For multiple comparisons, the Bonferroni correction, Tukey’s method, or the Least Significant Difference method was applied to adjust the p-values accordingly.
To investigate the association between DF intake and gallstones, DF intake was analyzed as a continuous variable (an increase of 10 g/day) and as a categorical variable (using quartiles) using weighted multivariable logistic regression analysis. Additionally, three analytical models were developed: Model 1, unadjusted for any covariates; Model 2, adjusted for participants’ demographic characteristics (age, gender, race, marital status, family income, and education level); and Model 3, which, based on Model 2, was further adjusted for all covariates, including BMI, TC, HDL-C, hypertension, diabetes, CHD, smoking status, sedentary activity, and dietary intake of total energy, total carbohydrates, total fat, and total protein.
DF intake was categorized into quartiles as a categorical variable, and trend tests were conducted using weighted multivariable logistic regression. Smooth curves were used to explore the linear relationship between DF intake and gallstones. Subgroup analyses and interaction tests were performed based on the specified subgroup variables to further assess the robustness of the results. All statistical analyses were conducted using R software (version 4.2.2, http://www.R-project.org, R Foundation) and Free Statistics software (version 2.1, Beijing, China, http://www.clinicalscientists.cn/freestatistics). A two-tailed P-value < 0.05 was considered statistically significant.
Results
Baseline characteristics of study population
This study included 8,782 participants. The average age of all participants was 48.811 ± 17.064 years, with females accounting for 51.28% of the sample. Table 1 presents the general baseline characteristics of the participants, stratified by quartiles of DF intake.
Table 1.
Weighted baseline characteristics of participants in this study (N = 8782)
| Characteristic | Dietary fiber intake (g/day) | P-value | ||||
|---|---|---|---|---|---|---|
| Total | Q1 (≤ 10.05) |
Q2 (10.05–14.65) |
Q3 (14.65–20.45) |
Q4 (> 20.50) |
||
| Number of participants | 8782 | 2176 | 2205 | 2189 | 2212 | |
| Age (years) | 48.811 (17.064) | 47.385 (16.862) | 48.759 (17.710) | 49.459 (16.994) | 49.531 (16.575) | 0.074 |
| Gender, n (%) | < 0.001 | |||||
| Male | 4080 (48.72) | 822 (38.83) | 930 (45.54) | 1024 (49.36) | 1304 (60.74) | |
| Female | 4702 (51.28) | 1354 (61.17) | 1275 (54.46) | 1165 (50.64) | 908 (39.26) | |
| Race, n (%) | < 0.001 | |||||
| Mexican American | 810 (7.71) | 119 (5.45) | 144 (5.79) | 233 (8.86) | 314 (10.59) | |
| Other Hispanic | 837 (8.03) | 219 (9.53) | 215 (7.55) | 193 (6.94) | 210 (8.25) | |
| Non-Hispanic White | 4246 (64.03) | 964 (60.33) | 1130 (67.22) | 1111 (64.83) | 1041 (63.41) | |
| Non-Hispanic Black | 1742 (10.45) | 613 (15.35) | 478 (11.36) | 368 (8.93) | 283 (6.48) | |
| Other Race | 1147 (9.79) | 261 (9.34) | 238 (8.08) | 284 (10.44) | 364 (11.27) | |
| Marital status, n (%) | < 0.001 | |||||
| Married/Living with Partner | 5072 (62.63) | 1069 (53.81) | 1243 (62.58) | 1316 (65.02) | 1444 (68.55) | |
| Widowed/Divorced/Separated | 2091 (18.16) | 619 (21.83) | 548 (18.11) | 506 (17.69) | 418 (15.21) | |
| Never married | 1619 (19.21) | 488 (24.37) | 414 (19.31) | 367 (17.30) | 350 (16.24) | |
| Education level, n (%) | < 0.001 | |||||
| High school below | 1160 (8.65) | 379 (12.08) | 256 (7.82) | 222 (5.61) | 303 (9.50) | |
| High school | 1905 (25.34) | 652 (34.76) | 517 (27.30) | 419 (24.11) | 317 (15.66) | |
| High school above | 5717 (66.01) | 1145 (53.16) | 1432 (64.89) | 1548 (70.28) | 1592 (74.84) | |
| Family income, n (%) | < 0.001 | |||||
| Low (PIR ≤ 1.3) | 2114 (18.30) | 767 (27.77) | 495 (17.75) | 442 (15.10) | 410 (13.26) | |
| Medium (PIR 1.3–3.5) | 3352 (34.72) | 848 (36.06) | 906 (36.67) | 847 (33.90) | 751 (32.32) | |
| High (PIR>3.5) | 3316 (46.99) | 561 (36.18) | 804 (45.58) | 900 (51.01) | 1051 (54.42) | |
| BMI, n (%) | < 0.001 | |||||
| ≤25 | 2216 (25.66) | 480 (22.83) | 515 (24.30) | 535 (25.20) | 686 (30.26) | |
| 25 ~ 30 | 2771 (32.47) | 607 (29.46) | 643 (30.70) | 736 (33.90) | 785 (35.60) | |
| >30 | 3795 (41.87) | 1089 (47.71) | 1047 (45.00) | 918 (40.90) | 741 (34.14) | |
| Total Cholesterol (mmol/L) | 4.873 (1.064) | 4.897 (1.090) | 4.844 (1.034) | 4.905 (1.066) | 4.844 (1.066) | 0.363 |
| HDL (mmol/L) | 1.389 (0.396) | 1.380 (0.402) | 1.409 (0.419) | 1.378 (0.369) | 1.391 (0.392) | 0.257 |
| Hypertension, n (%) | 0.080 | |||||
| Yes | 3411 (32.35) | 922 (34.49) | 893 (33.60) | 841 (32.15) | 755 (29.22) | |
| No | 5371 (67.65) | 1254 (65.51) | 1312 (66.40) | 1348 (67.85) | 1457 (70.78) | |
| Diabetes, n (%) | 0.167 | |||||
| Yes | 1294 (11.70) | 354 (12.28) | 338 (12.72) | 310 (11.90) | 292 (9.87) | |
| No | 7488 (88.30) | 1822 (87.72) | 1867 (87.28) | 1879 (88.10) | 1920 (90.13) | |
| CHD, n (%) | 0.480 | |||||
| Yes | 435 (4.25) | 113 (3.89) | 115 (4.90) | 96 (3.62) | 111 (4.61) | |
| No | 8347 (95.75) | 2063 (96.11) | 2090 (95.10) | 2093 (96.38) | 2101 (95.39) | |
| Smoke, n (%) | < 0.001 | |||||
| Yes | 3699 (40.14) | 1078 (48.80) | 938 (39.80) | 836 (35.31) | 847 (37.41) | |
| No | 5083 (59.86) | 1098 (51.20) | 1267 (60.20) | 1353 (64.69) | 1365 (62.59) | |
| Sedentary activity, (minutes/day) | 300 [240, 480] | 300 [180, 480] | 300 [240, 480] | 360 [240, 480] | 300 [240, 480] | < 0.001 |
| Dietary energy intake, (kcal/day) | 2069.700 (805.862) | 1490.483 (553.496) | 1918.880 (605.792) | 2194.901 (668.054) | 2642.861 (892.646) | < 0.001 |
| Dietary carbohydrate intake, (g/day) | 233.602 (102.454) | 160.653 (72.703) | 212.983 (79.637) | 247.619 (83.394) | 309.337 (109.957) | < 0.001 |
| Dietary fat intake, (g/day) | 86.206 (39.545) | 61.599 (26.990) | 80.258 (29.832) | 92.178 (35.775) | 109.382 (46.583) | < 0.001 |
| Dietary protein intake, (g/day) | 79.083 (33.421) | 58.165 (25.973) | 73.293 (25.703) | 83.615 (29.095) | 100.125 (37.185) | < 0.001 |
| Gallstones, n (%) | 993 (10.51) | 307 (13.51) | 272 (11.25) | 235 (10.23) | 179 (7.18) | < 0.001 |
Notes:
1. Abbreviation: Q, quartiles; PIR:the ratio of income to poverty; BMI:body mass index; CHD:coronary heart disease; HDL:high-density lipoprotein cholesterol
2. Data are presented as unweighted number (weighted percentage) for categorical variables and weighted mean (standard error) or median [IQR] for continuous variables
3. The P-value was calculated using a weighted data
Comparative analysis showed that for the higher DF intake groups, third (Q3: 14.65–20.45 g/day) and fourth (Q4: >20.5 g/day) quartiles groups, the average age was greater than that of the overall population. Furthermore, the average age gradually increased with higher DF intake. However, no statistically significant differences were observed among the four groups (P = 0.074). In the Q4 group with the highest DF intake, the proportion of men was 60.74%. As DF intake increased, the number of males in the corresponding group gradually increased, whereas the proportion of women decreased as DF intake increased.
Individuals who consumed more DF were more likely to be male, married/living with a partner, non-Hispanic white, with higher education levels, higher family income, and a BMI between 25 and 30. They were also more likely to be non-smokers and belong to populations with higher dietary intakes of total energy, protein, carbohydrates, and fat (all P values < 0.05). However, no significant differences were observed in TC, HDL-C, hypertension, diabetes, or CHD (all P values > 0.05).
In total, 993 participants had a history of gallstones (the weighted prevalence was 10.51%). Among the four groups, the weighted prevalence of gallstones was 13.51%, 11.25%, 10.23%, and 7.18%, respectively. A statistically significant difference in the prevalence of gallstones was observed among the groups based on DF intake (P < 0.001).
The association between DF intake and gallstones
The relationship between DF intake and gallstones is presented in Table 2. Based on the weighted logistic multivariable regression analysis results in the unadjusted model, DF intake was negatively associated with gallstone risk (OR = 0.76, 95% CI: 0.65–0.89, P = 0.001). After further adjusting for age, sex, race, marital status, family income, and education level, the association remained significant (OR = 0.83, 95% CI: 0.70–0.98, P = 0.033). Finally, after adjusting for all covariates, we found that for every additional 10 g/day of DF intake, the risk of gallstones was significantly reduced by 21% (OR = 0.79, 95% CI: 0.63-1.00, P = 0.047).
Table 2.
Weighted multivariable regression analysis of association between dietary fiber intake and gallstones
| Exposure | Weighted Total No. | Weighted Event (%) | Model 1 | Model 2 | Model 3 | |||
|---|---|---|---|---|---|---|---|---|
| OR (95% CI) | P-value | OR (95% CI) | P-value | OR (95% CI) | P-value | |||
| Dietary fiber intake per 10g/day increment | 199146921.353 | 20926155.80 (10.51) | 0.76 (0.65,0.89) | 0.001 | 0.83 (0.70,0.98) | 0.033 | 0.79 (0.63,1.00) | 0.047 |
| Dietary fiber intake categorical | ||||||||
| Q1 (≤ 10.05) | 46859929.059 | 6328626.31 (13.51) | Reference | Reference | Reference | |||
| Q2 (10.05–14.65) | 50429479.381 | 5675311.33 (11.25) | 0.81 (0.60,1.10) | 0.173 | 0.81 (0.59,1.11) | 0.179 | 0.76 (0.54,1.06) | 0.100 |
| Q3 (14.65–20.45) | 52756854.707 | 5395173.34 (10.23) | 0.73 (0.54,0.99) | 0.041 | 0.77 (0.56,1.05) | 0.094 | 0.69 (0.50,0.96) | 0.032 |
| Q4 (> 20.50) | 49100658.206 | 3527044.81 (7.18) | 0.50 (0.35,0.71) | < 0.001 | 0.60 (0.41,0.86) | 0.007 | 0.51 (0.32,0.83) | 0.010 |
| P for trend | < 0.001 | 0.006 | 0.006 | |||||
Notes:
Model 1 was the crude model without adjustment for covariates
Model 2 was adjusted for age, gender, race, marital status, family income and education level
Model 3 was adjusted as for Model 2, additionally adjusted for BMI, total cholesterol, HDL, hypertension, diabetes, coronary heart disease, smoking status, sedentary activity, dietary energy intake, dietary carbohydrate intake, dietary fat intake and dietary protein intake
95%CI: 95% confidence interval; OR: odds ratio;
P<0.05 indicates statistical significance
Curve fitting was used to illustrate the association between DF intake and gallstones (Fig. 2). Our results revealed a significant negative linear association between DF intake and gallstones (P = 0.003, P for non-linearity = 0.134).
Fig. 2.
Smooth curve fitting for probing dietary fiber intake and gallstones
When DF intake was categorized into quartiles for further analysis, we found that after adjusting for all covariates, a significant negative association between DF intake and gallstones remained. Compared with individuals in the lowest quartile (Q1) group (≤ 10.05 g/day), the adjusted OR values for gallstones in participants with DF intake in the second (Q2: 10.05–14.65 g/day), third (Q3: 14.65–20.45 g/day), and fourth (Q4: >20.5 g/day) quartiles groups were 0.76 (95% CI: 0.54–1.06, P = 0.100), 0.69 (95% CI: 0.50–0.96, P = 0.032), and 0.51 (95% CI: 0.32–0.83, P = 0.010), respectively. Moreover, trend tests confirmed the significance of this relationship (P < 0.05 in all three models).
Subgroup analysis and interaction testing
We conducted a subgroup analysis (Fig. 3) to assess the robustness of the association between DF intake and gallstones. This association remained unchanged across all subgroups and was more pronounced in men and those with diabetes and CHD.
Fig. 3.
Subgroup analysis of the association between dietary fiber intake and gallstones. Abbreviations: BMI, Body mass index; CHD, coronary heart disease
DF intake and gallstones in different genders
We further analyzed the relationship between DF intake and gallstones by sex in the US population. The average DF intake for men and women is 18 ± 10 g/day and 15 ± 7.8 g/day, respectively. Furthermore, statistically significant differences were observed in the occurrence of gallstones between male and female concerning DF intake (Fig. 4).
Fig. 4.
The association between dietary fiber intake and gallstones in male and female, respectively
Discussion
This nationwide, large-scale, cross-sectional study confirmed a negative linear relationship between DF intake and gallstone risk. Specifically, in the fully adjusted models for all covariates, every additional 10 g/day of daily DF intake was associated with a 21% reduction in the risk of developing gallstones. Trend tests further supported a dose-response relationship for this association. Subgroup and interaction analyses showed that the relationship between DF intake and gallstones remained consistent across the different subpopulations. These findings suggest that DF intake may independently predict gallstone risk. To the best of our knowledge, this is the first study to explore the association between DF intake and gallstones in a nationally representative sample.
Recently, there has been a growing interest in examining the relationship between dietary factors and gallstones [24]. It has been reported that the high prevalence of gallbladder stones may be attributed to increased dietary sugar and fat intake, along with a decreased consumption of whole grains and high-fiber foods [22, 24–26]. However, few studies have specifically investigated the effects of DF on the risk of gallstones. Tehrani et al. [24] conducted a case-control study to investigated the relationship between DF intake and gallstones, including 189 patients with gallstones in the experimental group and 342 matched controls without gallstones. The results showed that the odds of developing gallstones were significantly reduced in participants in the highest compared with the lowest tertile of DF intake (OR = 0.44, 95% CI: 0.37–0.7, P for trend = 0.015). Our results (OR = 0.51, 95% CI: 0.32–0.83, P for trend = 0.006) are consistent with those of Tehrani et al. However, they did not account for covariates, which might have led to confounding factors influencing their conclusion and preventing the independent quantification of the effect of DF intake on gallstones. In contrast, our study included a significantly larger number of participants, employed weighted analysis, and incorporated sufficient covariates across the three models, thereby enhancing the credibility and generalizability of these findings. Misciagna et al. also reached the same conclusion [27].
Previous studies have indicated that inflammatory responses and lipid metabolism disorders are important risk factors for gallstone formation [2, 3, 7, 28–30]. Oxidative stress is a critical factor involved in chronic inflammation. Alahmari et al. suggests that a high-fiber diet, particularly one rich in fruits and vegetables, helps counteract oxidative stress owing to its high antioxidant and phytochemical content. Moreover, it can effectively reduce inflammation levels by modulating inflammatory markers in the body [31]. Zhang et al. suggests that DF may reduce inflammatory responses by modulating the gut microbiota and its metabolic products, such as short-chain fatty acids [15]. Furthermore, previous studies have indicated that DF can significantly improve lipid metabolism by reducing low-density lipoprotein cholesterol (LDL-C) levels while having little effect on HDL-C levels [14, 31, 32]. Interestingly, some studies have suggested that HDL-C is beneficial for preventing gallstone formation, whereas LDL-C is a risk factor for their formation [33–36]. These findings are consistent with the role of DF in regulating blood lipids.
It is well known that obesity is an independent risk factor for gallstone formation [37, 38]. Studies have suggested that DF can increase satiety, improve gut microbiota, and regulate lipid metabolism, thereby alleviating obesity [31]. An increasing number of studies have shown that insulin resistance and diabetes are also independent risk factors for gallstone formation [39, 40]. Insulin resistance leads to hyperinsulinemia, which increases hepatic cholesterol uptake and raises the cholesterol saturation in the bile, thereby promoting gallstone formation [41]. Other studies have suggested that DF intake can improve insulin resistance [42–44]. Based on these studies, we are confident that DF can effectively prevent gallstone formation, as we found that DF exerts this effect through various factors that may contribute to gallstone formation.
Our study also found that the average daily DF intake for men and women in the US is currently 18 ± 10 g/day and 15 ± 7.8 g/day, respectively. However, the World Health Organization recommends a daily DF intake of ≥ 25 g for adults [45, 46]. Additionally, Barber et al. mentions that the recommended daily intake of DF for adults in most European countries and the US is 30–35 g for men and 25–32 g for women [43]. We observed that the current DF intake in the US population was far below the recommended levels, which might have contributed to the higher incidence of gallstones compared with other regions. Therefore, we encourage increased public education and the promotion of higher DF intake among adults to reduce the occurrence of gallstones and improve overall health.
Our findings are consistent with the broader body of evidence supporting the protective effects of DF in chronic disease prevention. Notably, recent literature has emphasized the integration of fiber-rich, plant-based dietary patterns into clinical care strategies as an effective means to improve patient outcomes. This reinforces the potential public health significance of promoting adequate dietary fiber intake among the general population [47].
Strengths and limitations
Our study has several strengths. First, we used the NHANES as the data source and employed a weighted analysis approach to ensure a large sample size and national representativeness of the results. Second, we included sufficient covariates that strongly supported the independent association between DF intake and gallstones, providing valuable guidance for personalized dietary recommendations for prevention. Subgroup analyses and interaction tests were conducted to ensure the robustness of the findings. Third, we found that the current DF intake among adults in the US is well below the recommended standard, highlighting the need for further health education efforts.
Nevertheless, our study has several limitations that should be considered. First, both DF intake and gallstone history were based on self-reported data, which may introduce recall bias and misclassification. Such biases could result in non-differential misclassification, potentially attenuating the observed associations and underestimating the true relationship between DF intake and gallstones. Moreover, some participants may not be aware of asymptomatic gallstones, leading to potential underreporting. Despite these limitations, self-reported data in NHANES have been widely used and validated in epidemiological research. Second, Although we adjusted for a wide range of relevant covariates, the possibility of residual confounding due to unmeasured variables—such as genetic predisposition, the specific types of DF (e.g., soluble vs. insoluble), and the intensity of physical activity—cannot be completely excluded. These factors may have influenced both dietary behaviors and gallstone formation, and their absence in our models may limit the precision of the observed associations. Third, given the cross-sectional design of this study, it is important to note that causal inferences cannot be made. Although we observed a significant association between DF intake and gallstones, the temporal relationship between exposure and outcome remains unclear. Therefore, our findings should be interpreted as correlations rather than evidence of a causal effect. Therefore, further large-scale prospective studies are needed to confirm the causal relationship and to assess whether these findings are observed in other populations.
Conclusion
A negative linear relationship exists between DF intake and gallstones in US adults. Furthermore, the current DF intake among Americans is well below the recommended levels. These findings highlight the association between DF intake and gallstones and emphasize the need for increased public education. Adults should consume more DF to maintain their overall health.
Abbreviations
- NHANES
National Health and Nutrition Examination Survey
- DF
Dietary fiber
- US
United States
- TC
Total cholesterol
- BMI
Body mass index
- HDL-C
High-density lipoprotein cholesterol
- LDL-C
Low-density lipoprotein cholesterol
- CHD
Coronary heart disease
- PIR
Income to poverty ratio
- OR
Odds ratio
- CI
Confidence interval
Author contributions
HML and TD conceived the idea and were responsible for designing the research. HML and CFM conducted the data analysis and drafted the paper. WF, YD were involved in the preparation of figures and tables. HWT was responsible for reviewing and editing, as well as funding sources. All authors read and approved the final manuscript.
Funding
This study was supported by the Gansu Provincial Health and Medical Research Project (Project No. GSWSQN2023-05) and the Lanzhou City Chengguan District Science and Technology Planning Project (Project No. 2022RCCX0014).
Data availability
No datasets were generated or analysed during the current study.
Declarations
Ethics approval and consent to participate
The data used in this study were obtained from NHANES, which involves publicly available, de-identified data and does not require additional ethical approval. The NHANES protocol was approved by the Institutional Review Board of the National Center for Health Statistics, Centers for Disease Control and Prevention.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
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References
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Associated Data
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Data Availability Statement
No datasets were generated or analysed during the current study.