2.1 Nutritional assessment before BS
Assessment of nutritional status of candidates to BS before the operation plays an important role in the post-surgical management. During the last few years, several studies demonstrated that patients with severe obesity often display micronutrient deficiencies (MDs) when compared to normal weight controls. In 2008, Asheim et al. analyzed the vitamin status of 110 patients affected by severe obesity as compared with 58 normal weight subjects: patients with obesity had significantly lower concentrations of vitamins A, B6, C, 25-hydroxyvitamin D, and lipid-standardized vitamin E [
4]. Similarly, Van Rutte et al. demonstrated in 200 patients affected by severe obesity that 38% of them had low serum iron, 24% had low serum folate, 11% had low serum vit. B12 and 81% had hypovitaminosis D (55% severe deficiency with a level < 30 nmol/l) [
5]. Finally, Peterson et al. demonstrated a frank deficiency of vitamin D (< 20 ng/mL) and iron (< 35 ug/dl for female and < 50 ug/dL for male) in 71.4% and 36.2% of 58 BS candidates [
6].
MDs in patients with severe obesity could be attributed to a poor-quality, non-varied, high-calorie and high-fat diet. For example, excessive simple sugar, milk products or fats could lead to a deficit of vitamin B1 [
7]. Moreover, iron status could be affected by adipose tissue inflammation and increased expression of the systemic iron regulatory protein hepcidin [
8]. Lastly, the increased adipose mass could act as a storage site for highly lipophilic molecules, such as vitamin D, and this could explain the difference in 25(OH)D levels between people with or without obesity [
9].
Assessment and correction of the nutritional status before the procedure in BS candidates is considered important for the prevention of post-bariatric MDs (see below). Indeed, Schiavo et al. recently reported that patients who received a pre-operative MDs correction did not develop new MDs in the first year after BS, whereas all patients who did not received MDs correction before BS continued to be deficient in one or more micronutrient after surgery, despite systematic post-operative supplementation [
10].
2.2 Controversies about pre-operative weight loss
Preoperative weight loss before BS is still a matter of debate. At present, most relevant guidelines do not provide any clear indication about pre-operative weight loss [
11,
12]. Indeed, guidelines agreed that a period of identifiable medical management is necessary in all patients prior to BS and that it is also necessary to assess patient’s motivation and willingness to adhere to follow-up programs, but a preoperative weight loss is never mentioned nor in the indication for BS nor in the preoperative evaluation [
11,
12].
The lack of clear indications for preoperative weight loss is probably related to the low evidence available on this topic. Therefore, we decided to perform a systematic analysis and we searched all articles identified as clinical trials and published in the last 10 years in PubMed with the terms “preoperative weight loss and obesity and/or bariatric surgery”. The search was conducted between June 1, 2019 and July 31, 2019 and all articles available in English were included. A total of 243 articles were retrieved: 111 duplicate articles were eliminated and further 84 were excluded because not related to the topic. Abstracts from the remaining articles where evaluated, leaving 25 full articles concerning weight loss prior surgery. After reading the full text, we concluded that only 7 out of 25 papers focused on the effects of weight loss prior to BS [
13‐
19], and only 3 of them were randomized control trials specifically comparing patients who achieved a significant weight loss before surgery with patients who did not [
13‐
15]. The characteristics of the three trials are reported in Table
1. Main aims of the trials were to assess if weight loss before surgery may improve the operating time [
13,
15], the intra-operative complications rate [
13], the surgeons perceived difficulty [
13], the 30 days post-operative complications [
13,
14], and the post-operative weight loss [
14,
15]. The three studies presented a large heterogeneity concerning the way in which weight loss was achieved: Van Nieuwenhove et al. compared patients randomly allocated to a 2-week preoperative VLCD regimen or no preoperative dietary restriction [
13], Kalarchian et al. compared patients receiving a 6-month behavioral lifestyle intervention to usual pre-surgical care [
14], and Coffin et al. evaluated the impact of an intra-gastric balloon (IGB) [
15]. As reported in the Table, the results are largely inconsistent for all the outcomes considered in the studies and no one single study observed a difference in post-operative weight loss between the intervention and the control arms.
Table 1
Results for specific outcomes in three randomised control trials specifically comparing patients who achieved a significant weight loss before surgery with patients who did not [
13‐
15]
Sample size | 273 | 143 | 115 |
Operating time | NS | / | NS |
Intraoperative complications | NS | / | / |
Surgeons perceived difficulty | Higher in control group vs. WL | / | / |
30-days post-operative complications | Higher in control group vs. WL | NS | / |
Post-operative WL | / | NS | NS |
Apart from the few randomized trials included in our meta-analysis, most of the works on the effects of weight loss prior BS on post-surgery weight loss are retrospective studies. Giordano & Victorzon compared patients who achieved different amount of pre-operative weight loss (< 5%, > 5 to 10% and > 10%) in a retrospective study with a total sample of 548 patients: post-operative weight loss was higher in patients who achieved > 10% weight loss at 12 months, with no significant differences observed at 24 months [
16]. Sherman WE et al. analyzed a cohort of 141 patients treated with sleeve gastrectomy (SG) and demonstrated that the percentage of excess BMI loss 1 year after SG was not statistically different between those who lost weight and those who gained weight before surgery [
20]. McNickle & Bonomo did not found any association between pre-operative weight loss and 1-year outcomes in a cohort of 127 patients treated with a standardized 6-month medical weight loss program and a 2-week pre-operative diet with meal replacements before SG [
21]. Moreover, the analysis of the data derived from the insurance mandated medical programs before BS conclude there is no evidence of any kind that insurance-mandated preoperative weight loss has any clear impact on postoperative outcomes or weight loss. For these reason, recently, the American Society for Metabolic and Bariatric Surgery published an update position statement on preoperative weight loss requirements where they conclude that “insurance-mandated preoperative weight loss is not supported by medical evidence and has not been shown to be effective for preoperative weight loss before bariatric surgery or to provide any benefit for bariatric outcomes” [
22].
In summary, we can conclude that at the moment evidences from randomized and retrospective studies do not to support the hypothesis that pre-operative weight loss could improve weight loss after BS surgery. Nevertheless, no large-scale, multicenter, randomized, controlled trials have been conducted so far on this specific topic. This does not mean that patient education and dietary counselling before and after BS are not useful (see below in Early, late and life-long Nutritional Management).
2.3 VLCD and VLCKD before BS may reduce surgical risk
Although BS has a low mortality rate, surgical complications (e.g., anastomotic leakage, bleeding, and infections) remain common (5–20%) and partly dependent on patient factors like age, sex, and comorbidity [
23]. Laparoscopic surgery in patients with severe obesity is challenging because of the thickness of the abdominal wall, intra-abdominal obesity, possible mesenteric thickening, and hepatomegaly [
24]. The presence of visceral fat can increase the complexity and risk in patients undergoing any type of abdominal surgery [
25]. Thickened abdominal walls may limit precise surgical movements during laparoscopy, and intra-abdominal obesity can limit visibility during surgical procedures. Nonalcoholic fatty liver disease (NAFLD) is a condition frequently complicating obesity that can lead to an increase in liver fat infiltration, mainly in the left lobe, making the liver brittle and more susceptible to injury and bleeding. During laparoscopic bariatric surgery, hepatomegaly and visceral fat in the left upper quadrant may limit preliminary exposure of the surgical field [
26‐
28] and may increase the conversion rate and operative time [
29]. The overall conversion rate in Roux-en-Y gastric bypass (RYGB) is approximately 4%, and an enlarged liver is responsible for approximately 50% of the conversions [
29].
In this contest, a modest weight loss of 5–10% in the immediate preoperative period has been suggested as a mean to facilitate surgery and reduce the risk of complications. Preoperative weight loss can be obtained with several regimens, such as low-calorie diets (LCD) (800–1200 kcal/day), very low-calorie diets (VLCD) (600 kcal/day), or a hypocaloric diet combined with IGB placement, and the question of which method provides the best results in terms of weight loss and patients’ compliance, tolerance, and acceptance is still under debate. The use of IGB prior to gastric banding surgery was described to significantly decrease the conversion rate and intra-operative complications in a matched case-control study [
30]. A pre-operative VLCD may also induce a significant weight loss before BS, being faster, cheaper, and with fewer side effects than IGB [
31]. Preoperative weight loss by means of a VLCD has been reported to reduce liver size and intra-abdominal fat mass, blood loss, short-term complications as well as operation time and length of hospital stay [
13,
26,
27,
32,
33]. However, a systematic review confirmed that VLCD led to a significant weight loss (− 2.8 to − 14.8 kg) and liver size reduction (5–20% of the initial volume), but did not found a reduction in peri-operative complications [
34]. Andrianzen Vargas et al. showed that LCD is insufficient in 60% of cases to achieve the intended 10% weight loss, while VLCD is able to achieve it in practically all patients [
31]. However, a more recent study comparing the effect of VLCD and LCD before surgery showed that, although VLCD was more effective in reducing total body weight (5.8 vs. 4.2%), there were no differences in terms of liver volume reduction, with both diets having similar effects on biochemical parameters, rate of surgical complications, and hospital length stay [
35].
More recently, very low-calorie ketogenic diet (VLCKD) has been proposed as a new effective and safe method for achieving effective preoperative weight loss. Previous studies reported that VLCKDs are effective for weight loss and safe in non-surgical contexts [
36]. On the other hand, it must be considered that any very low-calorie regimen drives a catabolic state and an increased oxidative stress that may have a negative impact on surgical outcomes. In addition, the ketogenic diet, based only on a protein substrate, may induce an adaptive response in several organs, with physiological modifications potentially unsafe in the perioperative period. To date only few studies addressed the role of VLCKD immediately before BS, and the available data are actually scarce. Leonetti et al. evaluated in an uncontrolled study the compliance, safety, and effectiveness of a sequential regimen (VLCKD for 10 days, followed by a VLCD for 10 days, and then a LCD for 10 days) in patients with obesity scheduled for BS. The study showed an adequate short-term reduction of body weight and waist circumference, without dangerous alteration in renal, hepatic, and metabolic functions. The weight loss was similar to that obtained with a VLCD and better than reported for LCD [
37]. A similar 30-day sequential preoperative regimen was used in another uncontrolled study showing a significant reduction in weight, waist circumference and visceral fat, and an improvement in several clinical parameters, including glycemic and lipid profiles. Moreover, a mean 30% reduction in liver volume was also observed [
38]. Finally, in a third non randomized study, patients were treated with either VLCKD or VLCD for 3 weeks prior to BS. Weight loss was not significantly better in the VLCKD than in the VLCD group, but VLCKD had better results on surgical outcomes, influencing drainage output, post-operative hemoglobin levels, and hospital stay. However, no data on the reduction of liver and visceral fat volumes were obtained in this study [
39].
In conclusion, there is a general agreement on the beneficial effects of a modest weight loss in the immediate pre-surgical period on the surgical and anesthesiological risks. Efficacy of VLCD regimens and IGB as bridging therapy before BS is consolidated in literature, while the role of VLCKD is arising in importance, but still under debate in the pre-operative period. Large randomized studies addressing these issues are needed, particularly aimed to accurately measure the effects on liver and visceral fat volumes changes.