Inguinal hernia, umbilical hernia, and ventral hernia (including incisional hernia and parastomal hernia) are the three types of hernias, according to the 10th revision of the International Classification of Diseases. Inguinal hernias are the most common hernias, and umbilical hernias are also frequent hernias (1). Incisional hernias occur after laparotomies at a rate of 5–20% and more than 30% in high-risk individuals (2). There have been many studies investigating risk factors for hernias (3–9), but few studies have analyzed the effects of dietary factors on hernias (10). Dietary factors are important factors affecting health and disease (11–14). Therefore, this study used the methods of Mendelian randomization (MR) to analyze the effect of dietary factors on hernias.

MR identifies the causal relationship between exposures and outcomes by employing genetic variations as instrumental variables (IVs). Three fundamental assumptions must be met for MR to function (15). First, there was no connection between the IVs and any probable confounding factors. Second, there must be robust correlations between the IVs and exposure variables. Third, there are no direct connections between the IVs and outcomes. As a result of using deidentified and freely accessible data from the IEU Open GWAS project, this study was exempt from institutional review board approval.

As shown in Supplementary Table S2, horizontal pleiotropy was detected in the analyses of the effects of fresh fruit intake on umbilical hernia and salt added to food on inguinal hernia (p < 0.05). The presence of horizontal pleiotropy indicated that these analyses violated the assumptions of MR and that there were direct associations between IVs and outcomes (18, 19). We will therefore treat them as invalid analyses. Utilizing the MR-PRESSO method, outliers were found in some analyses, but after removing the outliers and repeating the analyses, the results remained largely unchanged. The F statistics of IVs are all larger than 10, indicating that IVs and exposures have strong associations. The results of the MR-PRESSO method and F statistics are shown in the corresponding sections of Supplementary Table S2.

The associations between nutritional factors and the risk of hernias have not been extensively studied (10), regardless of the fact that diet is an important influencing factor of health (21–23). We only found one study from Turkey that focused on the relationship between dietary factors and hernias, and their study found that dietary factors such as cheese, red meat, chicken, nuts, and bread were associated with inguinal hernia (10). Their study included only 115 people with groin and only used 3-day food consumption records; Therefore, we believe that their study has some limitations. Dietary factors are difficult to measure. The UK Biobank used the frequency to measure dietary factors, more information is provided in Supplementary Table S1. As changing eating habits is difficult, it is highly difficult to use randomized controlled trials to evaluate the effect of dietary factors on hernias. Observational epidemiology is often used to analyze the influence of research factors on study subjects. However, the presence of confounders (24–26), reverse causality (27, 28), and other factors might bias the causal effects that observational epidemiology observed. The introduction of instrumental variables can effectively solve these shortcomings (29, 30). MR, an analysis that uses genetic variation as IVs, is being utilized increasingly frequently. MR sits between observational epidemiology and interventional epidemiology in the hierarchy of evidence (31). In this study, we used MR analysis methods to analyze the effects of 20 dietary factors on three common hernias. The results of this study suggest that alcohol intake has different effects on different hernias. Alcoholic drinks per week reduce the risk of inguinal hernia, alcohol intake frequency increases the risk of abdominal hernia, and alcohol intake does not have any effect on umbilical hernia. In some studies, there was no association between alcohol intake and developing inguinal hernia (32, 33). However, it was found in a different study that individuals with inguinal hernias consumed more alcohol (10). However, less than 1,000 cases of inguinal hernias were included in their analysis, which limited the credibility of their study. Our study included hundreds of thousands of individuals from the UK Biobank and the Finngen Biobank, therefore our study provided new evidence to clarify the relationship between alcohol intake and inguinal hernia. It is worth noting that the causal relationship between drinking frequency and ventral hernia may be influenced by a single SNP, as shown in Figure 1B. In addition, we found that non-oily fish intake increased the risk of inguinal hernia, salt added to food increased the risk of umbilical hernia, cheese intake, and dried fruit intake reduced the risk of ventral hernia, and cooked vegetable intake increased the risk of ventral hernia. It is important to note that neither the causality of non-oily fish consumption on inguinal hernia nor the causality of cooked vegetable intake on ventral hernia are particularly stable; they are affected by a single SNP. More information is shown in Figures 1E,F. We must be particularly careful when interpreting these findings. First, the causal relationship observed by the MR analysis is the consequence of prolonged exposure to dietary factors. Therefore, short-term exposure may not have any clinical effect. Second, the Two-sample MR analysis only revealed the overall effects of exposures on outcomes, not the direct effects. Extremely complex pathways may link exposures and outcomes.

Unavoidably, this study has several restrictions. First, we were incapable of assessing whether there was a U-shaped correlation (for example, as dried fruit intake increases, the risk of ventral hernia rises first and then decreases) between dietary factors and hernias due to continuous data on dietary factors being employed in this study. Second, due to the lack of GWAS data for the two demographics of sex and age, we were unable to conduct stratified analyses. Third, the inability to further divide dietary intake categories prevents a more detailed analysis. Fourth, because our analysis primarily focuses on individuals from Europe, extending our findings to other populations is difficult.

Alcoholic drinks per week will reduce the risk of inguinal hernia, while alcohol intake frequency will not affect the risk of inguinal hernia. Alcohol intake frequency will increase the risk of ventral hernia, while alcoholic drinks per week will not affect the risk of ventral hernia. Alcohol intake will not affect the risk of umbilical hernia. The intake of non-oily fish will increase the risk of inguinal hernia. Salt added to food will increase the risk of umbilical hernia. Cheese intake and dried fruit intake will decrease the risk of ventral hernia, while cooked vegetable intake will increase the risk of ventral hernia. No causal relationships were found with hernias from other dietary factors.

The original contributions presented in the study are included in the article/Supplementary materials, further inquiries can be directed to the corresponding author/s.

Ethical approval was not required for the study involving humans in accordance with the local legislation and institutional requirements. Written informed consent to participate in this study was not required from the participants or the participants’ legal guardians/next of kin in accordance with the national legislation and the institutional requirements.

YY: Data curation, Methodology, Formal analysis, Project administration, Validation, Funding acquisition, Resources, Visualization, Writing – original draft, Writing – review & editing. BH: Data curation, Methodology, Formal analysis, Project administration, Funding acquisition, Resources, Writing – original draft, Writing – review & editing. YW: Data curation, Methodology, Supervision, Conceptualization, Formal analysis, Project administration, Validation, Investigation, Funding acquisition, Resources, Visualization, Software, Writing – original draft, Writing – review & editing.