Colorectal cancer (CRC) is one of the most common gastrointestinal malignancies globally, ranking third in incidence and second in mortality (1). Although curative surgery remains the most effective treatment for colorectal cancer, the incidence of postoperative complications remains high, reaching up to 35% (2). These complications are not only related to the surgery itself but are also influenced by the patient’s overall health and other non-surgical factors.

After potentially curative surgery for colorectal cancer, prognosis and treatment decisions are typically based on tumor pathology. However, an increasing body of research indicates that tumor staging is not the only factor determining patient outcomes. Body composition has increasingly been recognized as playing an important role in prognosis. Body composition parameters, such as obesity, are strongly linked to the prognosis of colorectal cancer. Epidemiological studies have shown that obesity is a significant risk factor for colorectal cancer (3). Furthermore, obesity is considered a risk factor for postoperative complications in various abdominal surgeries (4). However, the impact of obesity on colorectal cancer prognosis remains controversial. Some studies report worse outcomes in both obese (5, 6) and underweight patients (7), while others have not observed such associations (8).

Visceral obesity (VO) refers to the excessive accumulation of intra-abdominal adipose tissue and is generally considered a more accurate indicator of obesity than body mass index (BMI) (9, 10). Due to its central role in metabolism and its potential impact on postoperative recovery, accurately measuring visceral fat may have significant clinical value in the preoperative risk assessment of colorectal cancer patients. Compared to traditional BMI, computed tomography (CT) provides a more precise and reproducible method for measuring visceral fat area (VFA) (11). In the preoperative evaluation of colorectal cancer patients, abdominal CT imaging is routinely used not only to screen for metastatic disease but also to assess visceral fat accumulation.

This study aims to conduct a systematic review and meta-analysis to explore the impact of VO, measured exclusively by CT imaging, on the prognosis of colorectal cancer patients. Specifically, the study will evaluate the predictive value of visceral obesity for both short-term outcomes, such as postoperative complications, and long-term outcomes, including overall survival (OS) and disease-free survival (DFS), following elective colorectal cancer surgery.

Obesity, being directly linked to several chronic illnesses and cancers, is a major global public health concern (40). Although BMI has long been the most commonly used metric for diagnosing obesity, it does not adequately reflect the distribution of fat in obese individuals. This is because obesity is characterized by an uneven distribution of fat tissue throughout the body, along with localized disruptions in fat and glucose metabolism (41). Obesity can be classified into two categories based on the location of fat accumulation: visceral obesity and peripheral obesity. The assessment of VFA through CT scanning is considered the gold standard for diagnosing visceral obesity, which is predominantly found in the abdominal region (42). Early studies have linked visceral fat to the incidence of CRC, the second most common cancer worldwide (43). However, the impact of VO on survival and surgical complications in colorectal cancer patients remains inconclusive (44, 45). Therefore, we conducted this meta-analysis to evaluate the effect of visceral obesity on postoperative outcomes in colorectal cancer.

We compared the data of colorectal cancer surgery patients with and without VO. We found that patients with VO experienced a longer recovery time for bowel movements, had fewer lymph nodes harvested, and had higher conversion rates. Additionally, the overall incidence of complications-including anastomotic leaks, intestinal obstruction, intra-abdominal abscesses, wound infections, and pulmonary complications-was significantly higher in patients with VO compared to those without. However, there was no difference in OS and DFS between the two groups.

The quantity of lymph nodes removed during tumor excision is a crucial predictor of oncological results in addition to demonstrating the surgeon’s ability. VFA influences the number of lymph nodes harvested, either because visceral obese patients have thicker mesenteries, which can make it difficult to see anatomical planes during surgery, making the surgical field more difficult and making it more difficult to dissect lymph nodes and identify blood vessels, which leads to fewer lymph nodes being harvested (14), or because fat tissue adheres to the mesentery, making it more difficult to identify lymph nodes in visceral obese patients (16). Despite the difficulty of dissecting lymph nodes, the operating time did not increase appreciably. The findings of meta-analyses that have already been published contradict this (46). We think that even with obese patients, the operational time can be reduced after a long learning period and overcoming the learning curve, even though the process is more complex.

In general, obesity, tumor size, and pelvic anatomical characteristics are the primary factors that contribute to the transition to open surgery (47, 48). Visceral obesity can further complicate the surgical field and operability, in addition to the challenges posed by limited anatomical features (49). This is specifically verified by our research.

Postoperative problems serve as critical indicators for evaluating short-term surgical outcomes, particularly in colorectal cancer surgery, where anastomotic leakage is a significant postoperative complication. Thickened mesentery, oversized omentum, and excessive visceral fat are frequently seen in patients with VO. VO is a significant predictor of surgical difficulties and patient outcomes because of these characteristics (50). Anastomotic leaking is more common in VO patients due to the increased technical difficulties of surgery caused by the growth in intra-abdominal fat. Furthermore, obesity raises intra-abdominal pressure for an extended period of time, which may hinder anastomotic site microcirculation and recovery (51). Metabolic problems are strongly associated with obesity, and the inflammatory state that these abnormalities cause may have a detrimental effect on anastomotic healing and tissue repair (52). Excess belly fat increases the risk of bowel blockage because it can impede or disrupt normal intestinal movement, which in turn increases the mechanical pressure on the intestines. Patients who are obese usually have thicker mesentery, which increases the risk of obstruction by causing insufficient blood flow to the intestines. According to research, inflammatory factors such IL-1α, IL-1β, and IL-1 receptor antagonists are more prevalent in human visceral fat tissue than subcutaneous fat tissue (53–55). Bowel obstruction is more likely to occur when the intestines are altered intraoperatively since this causes the release of these inflammatory substances. This also explains the delayed recovery of bowel function in the VO group, as evidenced by the prolonged time to first bowel movement after surgery. Furthermore, too much fat raises the danger of fat liquefaction and infection, which explains why wound and intra-abdominal infections are more common (56, 57).

Some negative outcomes can be improved with thorough preoperative evaluation and therapy. According to studies, visceral obesity can be successfully decreased by pharmaceutical therapies, dietary changes, exercise, and behavioral counselling (58). In addition to greatly reducing the risk of problems from surgery, preoperative reduction of visceral fat may also be taken into consideration for patients who have pneumonia or other pulmonary risk factors, especially if they are unable to bear additional respiratory harm. However, it takes time to reduce visceral fat, which may have negative consequences including tumor growth. As a result, it is crucial to perform a comprehensive evaluation of the patient’s general health and carefully consider the risks and timing of the intervention.

There is ongoing discussion over the effect of VFA on the long-term prognosis following colorectal cancer surgery. According to some research, VFA is a significant predictor of DFS following surgery for colorectal cancer (59) and is regarded as a separate risk factor for OS in patients undergoing adjuvant chemotherapy for the disease (60). Contrary to the above findings, new research indicates that patients with greater VFA scores actually have longer OS (44). Notably, our study’s findings indicate that there were no appreciable variations in long-term outcomes (OS and DFS) between the VO and non-VO groups among patients who had colon cancer surgery. There are several factors that affect the association between visceral fat and the long-term prognosis of colorectal cancer, some of which are not well supported by clinical data. We think that this association may be significantly influenced by variables including hormone levels (61), patient gender (62), and tumor stage (9). Visceral fat’s endocrine effects may encourage tumor growth and recurrence in patients with early and intermediate-stage cancer, which would lower OS and DFS. On the other hand, since cancer patients frequently have a negative energy balance and a larger visceral fat content may be advantageous for survival, a higher visceral fat content typically suggests superior nutritional reserves for patients with advanced disease. The long-term prognosis of patients with colorectal cancer may also be impacted by the notable variations in steroid hormone levels (such as testosterone and estradiol) between women before and after menopause. These hormones are strongly linked to fat deposition. Nevertheless, there is currently little clinical evidence to validate these putative determinants, and the study’s data set is small. To evaluate the effect of these factors on the long-term prognosis of patients with colorectal cancer, more extensive prospective studies are therefore required.

Considering the potential impact of our findings on clinical practice for colorectal cancer patients, this study highlights the importance of distinguishing between visceral and non-visceral obesity, which may lead to more targeted and effective interventions. By identifying visceral obesity as a key metabolic risk factor in colorectal cancer patients, clinicians can prioritize interventions such as lifestyle modifications or pharmacotherapy, especially for those with higher visceral fat accumulation. Furthermore, our findings may assist in the early identification of high-risk colorectal cancer patients for obesity-related comorbidities such as diabetes, cardiovascular diseases, and fatty liver, enabling more timely interventions and improving long-term outcomes. Moreover, incorporating the measurement of visceral fat into routine screening for colorectal cancer patients can help healthcare providers better stratify patient risks and personalize treatment strategies. Overall, this study emphasizes the importance of personalized obesity management, which could significantly improve clinical decision-making, patient outcomes, and public health interventions for colorectal cancer patients.

Among the limitations of this study are the following: (1) the definition of visceral obesity differed among the included studies (some defined it as VFA ≥ 100 cm², others as VFA ≥ 130 cm², and some studies classified it based on gender), (2) the surgical approaches used in the included studies varied (open surgery, laparoscopic surgery, and robotic surgery were used, which is another source of high heterogeneity and potential bias), and (3) there may be publication bias because the studies only included patients who had completed preoperative CT scans, while those without CT scans were excluded.

In summary, patients with VO who have colorectal cancer and have surgery tend to have fewer lymph nodes removed, higher conversion rates to open surgery, and more postoperative problems. Nevertheless, OS nor DFS seem to be substantially impacted by these factors. Large-scale, prospective research from other nations and areas are still required to confirm these findings and investigate the underlying mechanisms, though, because of sample size limits and regional diversity.