The omentum, a large apron of fatty tissue located in the abdomen, has become a focal point in the study of obesity and related metabolic disorders. Researchers are exploring whether removing the omentum, a procedure called omentectomy, can offer benefits beyond traditional weight loss methods. This article delves into the potential weight loss benefits of omentum removal, examining the evidence from various studies and considering the broader implications of this surgical approach.
The Omentum and Visceral Fat
The omentum is a significant source of visceral fat, the type of fat that surrounds internal organs. Visceral fat is considered metabolically active and has been linked to an increased risk of type 2 diabetes and cardiovascular disease. Abdominal obesity, reflecting the amount of visceral adipose tissue, has been identified as an independent risk factor for type 2 diabetes and cardiovascular disease.
Researchers at Vanderbilt University Medical Center are investigating the role of visceral fat in type 2 diabetes. Their studies suggest that the omentum may have a powerful effect on the liver, potentially influencing insulin production.
The Rationale Behind Omentum Removal
The increased metabolic risk of excess visceral adipose tissue is probably due to multiple underlying mechanisms. One hypothesis suggests that because visceral adipose tissue drains directly into the liver, it exposes the liver to increased levels of metabolites, particularly non-esterified fatty acids. Visceral adipose tissue displays increased lipolysis compared to subcutaneous depots. This prompted the hypothesis that removal of visceral adipose tissue in conjunction with bariatric surgery could have additional positive metabolic effects.
Animal studies have shown promising results with omentum removal. In these studies, researchers tested insulin sensitivity and how the liver and muscle metabolize sugar both before and after removing visceral fat. The researchers found the effect of the omentum on the liver is quite powerful. This is as effective in shutting down the liver production of insulin as insulin is, or as many of the drugs being used to treat type 2 diabetes.
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Omentectomy and Bariatric Surgery
Given the potential link between the omentum and metabolic health, some researchers have explored combining omentectomy with bariatric surgery, such as Roux-en-Y gastric bypass. Gastric bypass surgery leads to significant weight loss and a significant resolution of diabetes.
A study published in 2002 showed significantly improved glucose tolerance and insulin sensitivity in the group undergoing omentectomy. A five-year study funded by the National Institutes of Health will include 120 to 160 patients. Half of the participants will have their omentum removed along with gastric bypass surgery, half will not. In an effort to compare racial differences in type 2 diabetes, the study is seeking an equal number of African-American participants to Caucasian participants. The study is currently enrolling participants with type 2 diabetes who have been approved for gastric bypass surgery.
However, short-term studies (6-24 months) have refuted this notion.
Long-Term Effects of Omentectomy
A study involving 49 obese women who underwent gastric bypass surgery, with some randomly assigned to omentectomy, found no long-term beneficial effects of omentectomy in conjunction with gastric bypass operation 5 years post-operatively. There was a significant weight regain between the 2- and 5-year follow-up examinations, but no significant difference in body weight change between the two groups. In addition, there were no significant differences between the omentectomy and non-omentectomy group regarding total body fat, visceral adipose tissue, subcutaneous adipose tissue, fasting plasma glucose, insulin, insulin resistance, plasma lipids, or systolic blood pressure.
The rationale for why a long-term follow-up of these subjects was necessary is that following a rapid initial weight loss after gastric bypass, there is often a significant weight regain already, 1 year after the intervention. In addition, even though a majority of subjects experience remission of type 2 diabetes initially, a relapse in diabetes can sometimes be seen over time and it is possible that increased amounts of visceral adipose tissue could play a role in this.
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One possible explanation for the lack of long-term benefits is that the potential positive effects of removing approximately 0.5 kg of adipose tissue might be concealed by the overall much larger adipose tissue reduction following gastric bypass operation or the average small proportion that it constitutes of the baseline body weight (0.45%). Interestingly, 5 years post-operatively, there was no significant difference in visceral adipose tissue between the omentectomy group and non-omentectomy group, which could explain the lack of difference in metabolic parameters between the groups.
Omentectomy as Part of Cancer Surgery
Omentectomy is also performed as part of surgical procedures for certain cancers, particularly ovarian cancer. Ovarian cancers readily spread to the omentum early in their metastasis, so an omentectomy can be a part of a surgical staging procedure to see if early-stage cancer has spread. Even if abdominal imaging appears negative for metastatic tumor spread, surgeons may perform an omentectomy to ensure there is no microscopic evidence of peritoneal or omental spread.
The Surgical Procedure and Recovery
Omentectomy is usually performed as part of a larger cancer surgery and not as a separate procedure. The extent of the surgery and the recovery period depend on the patient's condition and what other procedures are performed.
When an omentectomy is performed during open abdominal surgery, patients usually spend two to three days in the hospital, followed by another four weeks of recovery at home. When an omentectomy is performed using minimally invasive surgical techniques that don’t require large incisions, the procedure can be done as an outpatient, or with overnight hospitalization.
During an omentectomy, the surgeon removes the omentum along with any other affected organs in an attempt to remove as much cancer as possible. Omentectomy is commonly combined with other operations, including hysterectomy, salpingectomy, oophorectomy, prostatectomy, gastrectomy, colectomy, retroperitoneal lymph node dissection, and cytoreductive or debulking surgery.
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After the surgery, patients typically spend several days recovering in the hospital. The surgeon will discuss the results of the surgery and any important laboratory findings with the patient, and together they’ll review the condition and the next steps in the treatment plan. Surgery for cancer is often followed by other cancer treatments to make sure that no cancer cells are left behind.
Omentectomy in Animal Studies: A Deeper Dive
To further explore the potential benefits of omentectomy, researchers have conducted extensive animal studies. These studies provide valuable insights into the mechanisms by which omentum removal may impact metabolic health.
Study Design and Methods
The animal studies typically involve comparing rats fed a high-fat diet (HFD) with and without omentectomy to control rats fed a standard chow diet (SCD). Researchers monitor various parameters, including body weight, food intake, plasma glucose, triglyceride, and insulin levels, as well as liver histology and gene expression.
Key Findings
Omentectomy reduced weight gain and prevented the development of MS and NAFLD in HFD-fed rats.
In rats undergoing omentectomy after two months on a HFD, food intake decreased significantly two months after surgery, and weight gain ceased immediately after omentectomy despite continuing on the same diet. Sixty days after surgery, body weight decreased significantly and this decrease persisted throughout the experimental period. Likewise, omentectomy was followed by a significant decrease in HOMA-IR and in plasma glucose, triglyceride, and insulin levels. Moreover, steatosis grade, hepatic triglycerides, and inflammation, apoptosis, and fibrogenesis markers also decreased significantly over the months following omentectomy.
Omentectomy and Food Intake
Food intake was significantly reduced in HFD-rats that underwent omentectomy. Omentectomy did not affect food consumption in SCD/O-rats. Fecal triglycerides were not significantly modified in rats on HFD-rats compared to SCD-rats, and omentectomy did not modify fecal triglycerides in these rats.
Gene Expression Analysis
Gene expression analysis revealed that the greater omentum expressed the genes coding for ghrl, Npy, Agrp, and Pmch, four orexigenic hormones. Moreover, the expression of Npy, Pmch, and Agrp was significantly higher in the greater omentum than in SCF. However, only the gene and protein expression of PMCH was significantly increased in the omental fat but not in the SCF of HFD-rats.
Plasma levels of AGRP, PMCH, and NPY were significantly elevated in HFD-rats and correlated to the gene expression in hypothalamus. GHRL plasma levels were markedly decreased in HFD-rats. In HFD-rats that underwent omentectomy, the plasma levels of all these orexigenic factors remained at control levels. Likewise, in HFD/O2-rats, the plasma levels of all these factors returned to normal within 75 days after omentectomy.
Leptin, Insulin, and Inflammatory Markers
Gene expression of lep, Ins, Tnf, Il6, Ptpn1, and Crp was significantly elevated in the omental fat of HFD-rats. However, this diet also increased gene expression for lep, Tnf, and Ptp1n in SCF. Only the protein expression of IL-6 and CRP was not increased in the SCF of HFD-rats. In fact, the protein expression of CRP was not detected in the SCF and omental fat of SCD-rats. On the contrary, IRS-1, a key molecule in insulin signaling, was detected in SCF, but not in omental fat. The absence of IRS1 in the omental fat was associated with increased lipolytic activity in this fat…
Considerations and Potential Risks
Currently, there are no known risks to removing the omentum. However, it's important to note that after an omentectomy, the "guardian of the abdomen" is no longer there, so subsequent surgeons might encounter scar tissue or the intestines first.