Does Perioperative Weight Loss Affect Liver Size?

Abstract & Commentary

By Nicole R. Basa, MD, Clinical Instructor, Department of Surgery, UCLA Division of Minimally Invasive and Bariatric Surgery. Dr. Basa reports no financial relationships relevant to this field of study.

Synopsis: This study demonstrates that preoperative weight loss via a low-carbohydrate diet may decrease liver size and friability. It provides a more favorable operative environment by decreasing the incidence of liver injuries due to difficulty in retracting a large fatty liver in bariatric and foregut surgery.

Source: Benjaminov O, et al. The effect of a low-carbohydrate diet on the nonalcoholic fatty liver in morbidly obese patients before bariatric surgery. Surg Endosc. 2007 [Epub ahead of print].

Background: Morbid obesity often causes nonalcoholic fatty liver disease (NAFLD), which can complicate gastric bypass and other foregut surgery.

Method: Fourteen candidates for bariatric surgery underwent a very low-carbohydrate diet for 4 weeks. A CT scan was performed before and after the diet period.

Results: CT scans of the liver showed an increase in mean liver density (P = 0.06) and a decrease in mean liver volume (P = 0.01). The mean density increase was greater in the left than in the right lobe.

Conclusions: Four weeks of a low-carbohydrate diet decreases the liver fat content and liver size, most notably in the left lobe. This reduction can facilitate the ease of bariatric and foregut procedures.


Several bariatric programs require perioperative weight loss to reduce the liver and omental fat size to allow for an easier operation. Oftentimes with patients who have higher BMIs, the liver tends to be enlarged and friable due to fatty infiltration. These 2 components of a liver with NAFLD may lead to inadvertent injury to the liver, as it is retracted to expose the angle of the upper stomach.

There are several accounts in the literature that demonstrate a decrease in liver size with dieting. Fris and colleagues showed that a low energy diet for 2 weeks before bariatric surgery reduced liver size measured by ultrasound.1 Nomura and colleagues demonstrated a reduction in liver volume via CT scan findings after patients were placed on a low calorie diet for 3 months.2

Interestingly, the type of low calorie diet may lend to more efficient early weight loss, as demonstrated by popular mainstream diets such as the Atkins and South Beach diets, which are high in protein and low in carbohydrate. Volek and colleagues reported that a low-carbohydrate diet had a greater effect than a low-fat diet on weight loss and body composition in overweight patients.3

This study demonstrates an objective account of the decrease in liver size after a 4-week, low-carbohydrate diet measured by CT. The left lobe, which is often retracted to expose the upper stomach, demonstrated an increased density which would be seen in a less fatty liver. The overall liver volume also decreased. In theory, these findings make a bariatric procedure safer and easier to perform.

Unfortunately, this study had only 14 patients. A larger sample size would confirm that a change in liver size occurs in most patients after a low-carbohydrate diet. Also, measuring operative parameters such as a decrease in OR time and a decreased incidence of liver injuries, would demonstrate the clinical importance of decreased liver size. Also, performing a liver biopsy intraoperatively to pathologically demonstrate a decrease in hepatic steatosis would also justify a preoperative low-carbohydrate diet. Measuring liver enzymes before and after the diet would also be good to demonstrate the decrease in liver inflammation noted by a decrease in transaminases.

This paper is a foundation for more objective evidence in the literature to demonstrate a decrease in liver size due to preoperative dieting prior to bariatric procedures. When patients are required to lose weight before a bariatric procedure, surgeons are often met with disappointment by the patient. They often respond to the request with, "if I could lose the weight I wouldn't be here to have the operation." Many surgeons note the anecdotal appearance of an easier and safer operation after the patient loses weight prior to having a bariatric procedure, and explains this to the patient. This paper lends some data that objectively demonstrates this.


1. Fris RJ. Preoperative low energy diet diminishes liver size. Obes Surg. 2004;14:1165-1170.

2. Nomura F, et al. Obesity-related nonalcoholic fatty liver: CT features and follow-up studies after low-calorie diet. Radiology. 1987;162:845-847.

3. Volek J, et al. Comparison of energy-restricted very low-carbohydrate and low-fat diets on weight loss and body composition in overweight men and women. Nutr metabol (Lond). 2004;1:13.