Efficacy of a liquid low-energy formula diet in achieving preoperative target weight loss before bariatric surgery

New Approaches to the Treatment of Severe Obesity-Prehabilitation as the Key to Success

PURPOSE OF REVIEW

Bariatric surgery (BS) has emerged as a crucial and effective treatment for severe obesity (SO), providing significant and sustained weight loss and improving comorbidities. Optimizing perioperative careparticularly through structured prehabilitation is crucial for improving surgical outcomes and long-term weight management. This review examines the role of prehabilitation, nutrition, psychological support, physical activity, and pharmacologic treatment in improving the effectiveness of BS.

RECENT FINDINGS

Despite the benefits of prehabilitation, there are significant differences in the way it is implemented in different healthcare centers. Protocols vary widely in terms of duration, components and intensity, leading to inconsistencies in patient preparation and postoperative recovery. Many patients still do not receive multidisciplinary support from dietitians, psychologists or physiotherapists prior to surgery, which can affect long-term outcomes. Barriers to effective prehabilitation include a lack of standardized guidelines, insufficient healthcare resources and limited patient adherence due to lack of awareness, low motivation or logistical constraints. Despite its proven benefits, structured prehabilitation lasting at least 3-6 months is not available to all patients, as access remains unequal and suboptimal in many healthcare settings. Prehabilitation is an important but underutilized component of BS preparation. Standardizing protocols and ensuring multidisciplinary, patient-centered support are essential to maximizing surgical benefit. Overcoming barriers such as healthcare system limitations, patient motivation and knowledge gaps is critical to integrating prehabilitation into routine bariatric care. This review emphasizes the need for evidence-based, multimodal prehabilitation strategies to improve perioperative care and long-term outcomes for BS patients.

Low-energy diets before metabolic bariatric surgery: A systematic review of the effect on total body weight, liver volume, glycemia and side effects

There is no consensus regarding energy content or duration of hypocaloric diets used for preoperative optimization of patients before metabolic bariatric surgery. In this systematic review, we aimed to compare the effect of different hypocaloric diets on reductions in total body weight, liver volume, glucose and insulin concentrations, and side effects. Six databases were searched for articles including adults with BMI ≥35 kg/m2 treated with hypocaloric diets before metabolic bariatric surgery. Hypocaloric diets were categorized as (1) low-energy diet containing 800-1200 kcal/day for 2-4 weeks, (2) very low-energy diet containing 450-<800 kcal/day for 2-4 weeks, and (3) low-energy diet containing 800-1200 kcal/day for >4 weeks. Thirty-three articles (1868 patients) were included, and if data were sufficient, synthesis without meta-analysis was conducted. A low-energy diet and very low-energy diet for 2-4 weeks resulted in similar reductions in total body weight, but longer treatment correlated to a more pronounced weight reduction. In addition, a low-energy diet for 2-4 weeks led to decreased liver volume, which might facilitate the surgical procedure. Insulin resistance was generally reduced after a low-energy diet for 2-4 weeks. However, most studies were within-group control, and since more than 60% of the studies lacked variance measures for our outcomes, we did not perform a meta-analysis. Accordingly, our results should be interpreted carefully. The protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO) with registration number: CRD42022295757; available at: https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=295757.

Preoperative Assessment of a Patient Undergoing Bariatric Surgery

Over the past few decades, obesity rates in the United States have risen drastically, and with this, there has been a rising demand for bariatric surgery. As such, anesthesiologists need to be familiar with the challenges presented by patients seeking bariatric surgery. Obesity causes pathophysiologic changes which may affect decision-making during the management of these patients. Patients seeking bariatric surgery also have a long, prescribed preoperative course that offers anesthesiologists the opportunity to be involved earlier during the pre-surgical evaluation and optimization process.

Very low energy diets prior to bariatric surgery may reduce postoperative morbidity: a systematic review and meta-analysis of randomized controlled trials

Purpose

To optimize patients prior to bariatric surgery, very low energy diets (VLEDs) are often employed for 2-4 weeks preoperatively. They are known to result in preoperative weight loss, decrease liver volume, and decrease surgeon-perceived operative difficulty. Their impact on postoperative morbidity has been less extensively studied. We performed a focused systematic review and meta-analysis with the aim of comparing preoperative VLEDs prior to bariatric surgery with controls in terms of overall postoperative morbidity.

Methods

MEDLINE, Embase, and CENTRAL were searched from database inception to February 2023. Articles were eligible for inclusion if they were randomized controlled trials (RCTs) comparing postoperative morbidity in adult patients (i.e., over the age of 18) receiving a VLED with liquid formulation to those receiving a non-VLED control prior to elective bariatric surgery. Outcomes included overall 30-day postoperative morbidity and preoperative weight loss. An inverse variance meta-analysis was performed with GRADE assessment of the quality of evidence.

Results

After reviewing 2,525 citations, four RCTs with 294 patients receiving preoperative VLEDs with liquid formulation and 294 patients receiving a non-VLED control met inclusion. Patients receiving VLED experienced significantly more preoperative weight loss than patients receiving control (mean difference (MD) 3.38 kg, 95% confidence interval (CI) 1.06-5.70, p = 0.004, I² = 95%). According to low certainty evidence, there was a non-significant reduction in 30-day postoperative morbidity in patients receiving VLED prior to bariatric surgery (risk ratio (RR) 0.67, 95%CI 0.39-1.17, p = 0.16, I² = 0%).

Conclusion

The impact of preoperative VLEDs on postoperative outcomes following bariatric surgery remains unclear. It is possible that VLEDs may contribute to decreased postoperative morbidity, but further larger prospective trials are required to investigate the signal identified in this study.

Comparison of a pre-bariatric surgery very low-calorie ketogenic diet and the Mediterranean diet effects on weight loss, metabolic parameters, and liver size reduction

This study compared the effects on weight as well as on metabolic parameters and liver size of a very low-calorie ketogenic diet versus a Mediterranean diet in patients with morbid obesity preparing to undergo bariatric surgery. This prospective comparison study evaluated patients 18-65 years of age who enrolled for bariatric surgery. Study duration was limited to an immediate preoperative period of 15 days. The very low-calorie ketogenic diet incorporated 10-12 kcal/kg/day of energy and 1-1.2 g/kg of protein using Kalibra (Societa Dietetica Medica) (VLCKD-SDM). The Mediterranean diet (MD) included 15-20% protein, 45-50% carbohydrate, and 25-35% fat. Changes in body mass index (BMI), liver size, and anthropometric and metabolic measurements were assessed. Between January 2016 and March 2017, of 45 patients enrolled, 30 completed the study (VLCKD-SDM, n = 15; MD, n = 15). Respective median BMI loss after VLCKD-SDM was 2.7 kg/m² versus MD 1.4 kg/m² (p < 0.05); median fat percentage reduction was 3.2 units versus 1.7 units (p < 0.05). Median liver size decreased 5.5% in the VLCKD-SDM group versus 1.7% in the MD group (p < 0.05). Median total cholesterol, and LDL levels decreased in both groups (p < 0.05), with greater relative decreases in the VLCKD-SDM group. Short-term preoperative diet-based weight loss in patients with morbid obesity preparing for bariatric surgery was significantly greater following a very low-calorie ketogenic diet versus a Mediterranean diet. The very low-calorie diet also significantly improved anthropometric and metabolic parameters and reduced preoperative liver size above that of the MD.

Anesthesia and Enhanced Recovery After Surgery in Bariatric Surgery

The Enhanced Recovery After Surgery Society published guidelines for bariatric surgery reviewing the evidence and providing specific care recommendations. These guidelines emphasize preoperative nutrition, multimodal analgesia, postoperative nausea and vomiting prophylaxis, anesthetic technique, nutrition, and mobilization. Several studies have since evaluated these pathways, showing them to be safe and effective at decreasing hospital length of stay and postoperative nausea and vomiting. This article emphasizes anesthetic management in the perioperative period and outlines future directions, including the application of Enhanced Recovery After Surgery principles in patients with extreme obesity, diabetes, and metabolic disease and standardization of the pathways to decrease heterogeneity.

Lower Interstitial Glucose Concentrations but Higher Glucose Variability during Low-Energy Diet Compared to Regular Diet-An Observational Study in Females with Obesity

This is an observational study of interstitial glucose (IG) concentrations, IG variability and dietary intake under free-living conditions in 46 females with obesity but without diabetes. We used continuous glucose monitoring, open-ended food recording and step monitoring during regular dietary intake followed by a low-energy diet (LED). Thirty-nine participants completed both study periods. The mean BMI at baseline was 43.6 ± 6.2 kg/m2. Three weeks of LED resulted in a mean weight loss of 5.2% with a significant reduction in diurnal IG concentration but with greater glycemic variability observed during LED. The mean 24 h IG concentration decreased from 5.8 ± 0.5 mmol/L during the regular diet period to 5.4 ± 0.5 mmol/L (p < 0.001) during LED, while the mean amplitude of glycemic excursion increased from 1.5 ± 0.7 to 1.7 ± 0.7 mmol/L (p = 0.031). The positive incremental area under the curve at breakfast was significantly larger for LED compared to regular diet. The daily fiber intake and the glycemic index of breakfast meals were significantly associated with the glycemic variability during regular dietary intake. In conclusion, the 24 h mean IG concentration was lower but with more pronounced glycemic variability during LED compared to a regular diet.

Effective and safe reduction in visceral fat using a formula diet in a short period before highly invasive endoscopic surgery - Case series

Introduction

We retrospectively assessed the efficacy and safety of use of short-term formula diet therapy to achieve preoperative reduction in visceral fat immediately prior to highly invasive endoscopic surgery.

Presentation of case

We reviewed 5 cancer patients who underwent thoracoscopic and/or laparoscopic-assisted esophagectomy or gastrectomy. The cases were those with a BMI ≥30 kg/m² or waist circumference ≥100 cm. Patients replaced one meal out of the three main meals with one or two sachets of formula diet (170–340 kcal). The other two meals were set to 600 kcal. The dietary therapy was implemented approximately 1 month before the operation. Weight loss achieved after dietary therapy ranged from 6.4% to 14.1% (p < 0.01). With the exception of one case, the decrease in visceral fat area ranged from 17.0%–40.7% (p = 0.03). Postoperative complications were anastomotic insufficiency in two cases.

Discussion

Although the decreases of the visceral fat were effectively implemented, the adverse effects on postoperative complications must be examined in the farther study.

Conclusion

It was suggested that use of formula diet to achieve preoperative visceral fat reduction in a short period of time immediately prior to highly invasive endoscopic cancer surgery would be an effective and safe strategy.

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We assessed efficacy of formula diet therapy to highly invasive endoscopic surgery.

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The decrease in visceral fat area ranged from 17.0% to 40.7% (p = 0.03).

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It should be emphasized that there were no more serious life-threatening cardiopulmonary complications.

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Preoperative formula diet therapy may be an effective means to reduce visceral fat.

Comprehensive care of a patient with obesity of BMI >70 kg/m2

A 31-year-old woman, with a body mass index of 70.31 kg/m², presented with progressive worsening of dyspnoea for 3 days. She had multiple comorbidities, including obesity hypoventilation syndrome. The patient developed type II respiratory failure with respiratory acidosis along with multiorgan failure. She was intubated and put on a mechanical ventilator and treated with intravenous diuretics, subcutaneous low-molecular-weight heparin and other supportive measures. Later, she was on noninvasive, continuous positive airway pressure ventilation overnight. She was prescribed a very-low-calorie diet along with physiotherapy and exercise. The patient underwent bariatric surgery 2 months after resolution of acute illness. Ten months after surgery, her body weight reduced from 180 kg to 121 kg, and her general condition improved. Successful management before and after surgical intervention depends on multidisciplinary teamwork, which includes the dietician, physiotherapist, endocrinologist, pulmonologist, nursing care and other supportive care.

Body Composition Changes Following a Very-Low-Calorie Pre-Operative Diet in Patients Undergoing Bariatric Surgery

BACKGROUND

Fatty liver in obese patients increases the technical difficulty of bariatric surgery. Pre-operative weight loss with a very-low-calorie diet (VLCD) is commonly used to facilitate surgery. Few studies have quantified the systemic effect of rapid pre-operative weight loss on body composition. The objective of this study is to evaluate body composition changes in bariatric surgery patients undergoing a VLCD.

METHODS

Body composition assessments were performed between August 2017 and January 2019 using dual-energy X-ray absorptiometry immediately before and after a 2-week VLCD at St Vincent's Hospital Melbourne. Data collected prospectively pre- and post-VLCD included total body weight, excess body weight, body mass index (BMI), lean body mass (LBM), fat mass (FM) and bone mineral content (BMC). The pre- and post-operative results were compared.

RESULTS

Forty-four patients completed both the 2-week VLCD and body composition assessments. Following a 2-week VLCD, patients lost a mean of 4.5 kg (range - 0.3 to 9.5) in a total body weight and 8.8% (range - 0.9 to 17.1) of excess body weight, with a mean reduction in body mass index of 1.6 kg/m² (range - 0.2 to 3.1). Loss of LBM was 2.8 kg and was significantly greater than loss of FM, 1.7 kg (p < 0.05). BMC changes were insignificant.

CONCLUSION

A VLCD is an effective tool for pre-operative weight reduction. In this cohort, a large amount of the total weight loss was attributed to a loss of lean body mass. The impact of significant lean body mass loss and its relationship to short- and long-term health outcomes warrants further assessment.

Impact of Exercise on Body Composition and Cardiometabolic Risk Factors in Patients Awaiting Bariatric Surgery

BACKGROUND

The role of exercise to achieve weight reductions in patients awaiting bariatric surgery has been little studied. The aim of this study was to describe the effects of an exercise program on body composition and cardiometabolic risk factors in patients awaiting bariatric surgery.

METHODS

Twenty-three patients awaiting bariatric surgery were divided into two groups: (a) an exercise group (EG, n = 12) and (b) a control group (CG, n = 11). Both groups received the usual care prior to surgery, but the EG also performed a 12-week exercise program which combined endurance and resistance training. Body composition, cardiometabolic risk factors, physical fitness, basal metabolic rate, and quality of life were assessed at baseline and at the end of the study.

RESULTS

After the exercise program, the EG achieved significant reductions in total weight (- 7.3 ± 4.1 kg, P < 0.01), fat mass (- 7.1 ± 4.7 kg, P < 0.01), and waist circumference (- 5.3 ± 2.1 cm, P < 0.01), while they maintained their fat-free mass and basal metabolic rate levels. Only the EG showed reductions in HbA1c (- 0.4 ± 0.45%, P < 0.05), systolic (- 10.5 ± 12.7 mmHg), and diastolic blood pressure (- 3.9 ± 5.2 mmHg, P < 0.05), as well as a decrease in waist-to-height ratio (- 0.032 ± 0.12, P < 0.01) and an improvement in quality of life.

CONCLUSIONS

The implementation of an exercise program prior to bariatric surgery reduces fat mass and central obesity and improves cardiometabolic risk factors and quality of life, especially in the physical scales.

TRIAL REGISTRATION

The study was registered at ClinicalTrials.gov (NCT03613766).

Influence of Preoperative Weight Loss on Outcomes of Bariatric Surgery for Patients Under the Enhanced Recovery After Surgery Protocol

INTRODUCTION

The enhanced recovery after surgery (ERAS) protocol, which emphasizes preoperative interventions, is safely implemented in patients undergoing bariatric surgery. Patients are additionally encouraged to achieve weight loss preoperatively. We aimed to identify factors contributing to preoperative weight loss and assess their influence on outcomes of bariatric surgery among patients under the ERAS protocol.

MATERIALS AND METHODS

We reviewed a prospectively created database in two bariatric centers with 909 bariatric patients treated in accordance with ERAS principles. The database included demographic characteristics, factors related to the surgery or perioperative period, and short-term outcomes. Our endpoints included analyses of (1) factors potentially contributing to preoperative weight loss and (2) the influence of preoperative weight loss on short-term outcomes of bariatric treatment.

RESULTS

Diabetes mellitus (p = 0.007), obstructive sleep apnea (p < 0.001), and previous surgery (p = 0.012) were identified as predictors of preoperative weight loss. Steatohepatitis (p < 0.001) and respiratory disorder (p = 0.004) decreased the chance of achieving satisfactory preoperative body mass reduction. Except for operative time, early outcomes of bariatric surgery were not influenced by preoperative weight loss. Patients who achieved preoperative weight loss were less likely to be lost to follow-up (p = 0.023). Postoperative weight loss was better in patients who could lose ≥ 5% total weight preoperatively (p = 0.009).

CONCLUSION

Unsatisfactory preoperative weight loss among patients treated under ERAS principles is not associated with increased risk of complications. Satisfactory preoperative weight loss predicts superior postoperative weight loss and follow-up participation.

The Efficacy of Energy-Restricted Diets in Achieving Preoperative Weight Loss for Bariatric Patients: a Systematic Review

In bariatric practice, a preoperative weight loss of at least 5% is recommended. However, the hypocaloric diets prescribed vary and no consensus exists. This study examined the efficacy of preoperative diets in achieving 5% weight loss. From a systematic literature search, eight randomised controlled trials (n = 862) were identified. Half of the trials used a "very-low-calorie diet" whilst the rest employed a "low-calorie diet". Only five diets achieved ≥ 5% weight loss over varying durations and energy intakes. By inference, compliance with a 700-1050 kcal (2929-4393 kJ) diet, consisting of moderate carbohydrate, high protein and low/moderate fat, for 3 weeks is likely to achieve 5% weight loss. A low-carbohydrate diet (< 20 g/day) may achieve this target within a shorter duration. Additional research is required to validate these conclusions.

Predictors of successful weight loss with relative maintenance of fat-free mass in individuals with overweight and obesity on an 8-week low-energy diet

A low-energy diet (LED) is an effective approach to induce a rapid weight loss in individuals with overweight. However, reported disproportionally large losses of fat-free mass (FFM) after an LED trigger the question of adequate protein content. Additionally, not all individuals have the same degree of weight loss success. After an 8-week LED providing 5020 kJ/d for men and 4184 kJ/d for women (84/70 g protein/d) among overweight and obese adults, we aimed to investigate the relationship between protein intake relative to initial FFM and proportion of weight lost as FFM as well as the individual characteristics associated with weight loss success. We assessed all outcomes baseline and after the LED. A total of 286 participants (sixty-four men and 222 women) initiated the LED of which 82 % completed and 70 % achieved a substantial weight loss (defined as ≥8 %). Protein intake in the range 1·0-1·6 g protein/d per kg FFM at baseline for men and 1·1-2·2 g protein/d per kg FFM at baseline for women was not associated with loss of FFM (P = 0·632). Higher Three-Factor Eating Questionnaire (TFEQ) hunger at baseline and reductions in TFEQ disinhibition and hunger during the LED were associated with larger weight loss (all P ≤ 0·020); whereas lower sleep quality at baseline predicted less successful weight loss using intention to treat analysis (P = 0·021), possibly driven by those dropping out (n 81, P = 0·067 v. completers: n 198, P = 0·659). Thus, the protein intakes relative to initial FFM were sufficient for maintenance of FFM and specific eating behaviour characteristics were associated with weight loss success.

Preoperative weight loss program targeting women with overweight and hypertrophy of the breast - a pilot study

Among women with hypertrophic breasts, the clear majority are overweight or obese. Owing to increased risk of complications, women with a body mass index (BMI) above 25 kg m ^-2 are precluded from reduction mammaplasty. The primary aim was to investigate if intensive weight loss could ready women with overweight for breast reduction surgery. Six women, all overweight [BMI 30.9 {28.5; 35.8} kg m ^-2 ] with symptomatic hypertrophy of the breast, were included a 12-week weight loss program. All women desired reduction mammaplasty and were motivated for preoperational weight loss. The first 8 weeks consisted of a formula-based diet supplying 800 kcal daily, in the subsequent 4 weeks regular foods were reintroduced increasing the intake to 1200 kcal daily. Five women completed the trial, and achieved a median (range) weight loss of 10.2 (6.5; 19) kg. Initial breast volume was 1100-2500 mL per breast, this was reduced by 300 (200; 500) mL after the intervention; equivalent to approximately 19%. Waist, hip, upper arm and thorax circumference were significantly reduced following weight loss. At end of study, all the women still suffered from symptomatic breast hypertrophy to substantiate reduction mammaplasty. Surgeries were performed 2 months thereafter. A 12-week intensive preoperative weight loss program enabled women with obesity for breast reduction surgery. Breast size was reduced proportionally more than total weight loss among women with hypertrophy.

Nutrient deficiencies prior to bariatric surgery

PURPOSE OF REVIEW

The purpose of this review is to provide an update of recent additions to our understanding of the prevalence of nutrient deficiencies and the potential role of preoperative weight loss in contributing to these deficiencies in obese individuals planning to undergo bariatric surgery.

RECENT FINDINGS

Recent reports that have included bariatric surgery candidates from sites around the world have shown consistent deficiencies in a variety of nutrients. Although protein-energy malnutrition is uncommon preoperatively, micronutrient deficiencies occur commonly with multiple deficiencies often present in the same individual. No difference in the prevalence of deficiency between men and women is apparent, and a standard profile of susceptibility to deficiency has not been identified. In the only studies that have evaluated dietary intake of total energy, macronutrients and micronutrients preoperatively, despite an excess of calories ingested, micronutrient intake tends to be lower than recommended.

SUMMARY

A high prevalence of micronutrient deficiencies, especially vitamin D, folate, B12 and iron, is present in obese individuals being considered for bariatric surgery. Despite high-caloric intake, the deficiencies present appear to be related to the poor quality of the diet and low micronutrient intake. These findings strengthen prior recommendations of routine preoperative nutritional screening. Because a standard profile of susceptibility to deficiency has not been identified, extensive nutritional screening, including micronutrient testing, should be considered in all patients in the preoperative setting. Finally, we recommend early supplementation of vitamins and minerals based on laboratory assessment and incorporation of a program to optimize eating behaviors prior to surgery.

Optimization of bodyweight before visceral surgery in obese patients

It's time to pay attention to this

Predictors of preoperative weight loss achievement in adult bariatric surgery candidates while following a low-calorie diet for 4 weeks

BACKGROUND

Achieving program-mandated preoperative weight loss poses a challenge for many bariatric surgery candidates. No systematic method exists to identify at-risk patients early in preoperative care.

OBJECTIVES

This study sought to explore predictors of preoperative weight loss achievement and to develop a treatment algorithm for guiding clinical decision-making.

SETTING

Greenville Health System, South Carolina.

METHODS

A retrospective chart review was conducted for 378 patients who followed a program-mandated low-calorie diet (LCD) for 4 weeks to achieve≥8% excess weight loss (EWL). Associations between weight loss achievement and patient demographic, nutrition, psychological, clinical, anthropometric, and treatment characteristics documented at 5 preoperative evaluation events were analyzed using logistic regression.

RESULTS

During the LCD, 62.7% of patients achieved≥8% EWL. Independent predictors of achievement (all P<.05) were male sex (OR 2.31, 95% CI 1.21-4.42), Caucasian race (OR 2.45, 95% CI 1.38-4.34), body mass index (BMI) at surgeon evaluation (50.0-59.9 kg/m²: OR .44, 95% CI .20-.97;≥60 kg/m²: OR .15, 95% CI .05-.42), number of co-morbidities (OR .83, 95% CI .74-.93), hypertension diagnosis (OR 2.42, 95% CI 1.42-4.13), prediet weight change (OR 1.08, 95% CI 1.01-1.16), and time between surgeon evaluation and preoperative LCD initiation (61-90 d: OR .46, 95% CI .23-.93).

CONCLUSION

Patients of female sex or non-Caucasian race; with a BMI≥50 kg/m², many co-morbidities, or no hypertension diagnosis at surgeon evaluation; who demonstrate prediet weight loss or extended wait time between surgeon evaluation and preoperative LCD initiation may be at risk for preoperative weight loss failure and may require preemptive diet modification to improve outcomes.