**2. Outcomes of bariatric surgery**

#### **2.1 Weight loss**

Weight loss is the primary goal of bariatric surgery. Regardless of the procedure, bariatric surgery provides significant long-term weight loss compared to non-surgical therapies [3].

There is no standardized metric for reporting weight loss. In surgical literature, it is frequently reported as the percentage of excess weight loss (EWL) as shown in Eq. (1) [4]

$$\begin{array}{l} \text{9\%} EWL = \left(\text{Pre-barrier survey}\right) \text{(BS) weight} - \text{Post-BS weight} \right) / \\ \left(\text{Pre-BS weight} - \text{ideal body weight}\right) \* 100 \end{array} \tag{1}$$

Ideal body weight is conventionally determined by using Metropolitan Life Tables [5] or the method of the Devine [6].

Some authors used percentage excess body mass index (BMI) loss (as shown in Eq. (2)) [4],

$$1\,\%\text{BMIL} = \left(\text{Pre BSBMI} - \text{Post BSBMI}\right) / \left(\text{Pre BSBMI} - 25\right) \* 100\tag{2}$$

In the medical literature, weight loss is reported as a percentage of total weight loss (TWL) expressed as Eq. (3) [4],

$$\text{\textbullet}\,T\,\text{WL} = \left(\text{Pre}\,\text{BS}\,\text{weight} - \text{Post}\,\text{BS}\,\text{weight}\right) / \text{Pre}\,\text{BS}\,\text{weight} \* \mathbf{100} \tag{3}$$

These parameters have limitations; however, %TWL is most frequently reported in contemporary literature.

Weight loss post-bariatric surgery is highly variable. Initially, a rapid weight decline is observed in the first 6 months, reaching a peak at 12 months. Then it slows down and reaches a plateau between 1 and 1.5 years (see **Table 1**).

Weight loss after RYGB & SG is comparable. Swiss multicenter bypass or sleeve study (SM-BOSS) [8] reported similar weight loss after RYGB and SG at 2, 3 and 5 years. Improvements in metabolic outcomes such as remission of diabetes mellitus (DM), hypertension (HTN) and hyperlipidemia were also comparable.

Laparoscopic Sleeve Gastrectomy vs. laparoscopic Roux en Y gastric bypass (SLEEVEPASS) study [9] showed greater excess weight loss with RYGB compared to SG (55 vs. 47% at 7 years).

Observational studies illustrate higher weight loss with RYGB than SG [10, 11]. It is likely related to the study design.

Weight loss with AGB is slower, reaching a plateau at 2 years [7]. The longitudinal assessment of bariatric surgery (LABS) study [12] compared RYGB and laparoscopic AGB in a cohort of 2348 obese individuals. At seven years, the mean weight loss with


**Table 1.**

*Expected weight loss after bariatric surgery [7].*

*Outcomes of Bariatric Surgery DOI: http://dx.doi.org/10.5772/intechopen.105734*

RYGB was 38.2 kg (95% CI, 36.9–39.5) and 18.8 kg (95% CI 16.3–21.3) after AGB. Due to lack of efficacy, the reoperation rate was higher in the AGB group than in the RYGB group (n = 160 vs. 14).

Adjustable gastric banding has gone out of practice due to lack of efficacy.

Most of the patients will regain some weight regardless of the operation commencing in the second year. It is estimated to be 5–10% of TBW in the first 10 years; e.g., in the Swedish obese subjects (SOS) study, the TWL decreased from 32 to 25% at 10 years after RYGB [13]. Similarly, in the LABS study, TWL decreased from 35 to 28% after RYGB [12].

What is the significant weight regain is not clearly defined in the literature. The risk of weight regain is lowest for RYGB (2.5 to 3.3%), followed by SG (12.5 to 14.5%) and highest for AGB (30.5 to 36%) [10, 14].

#### **2.2 Metabolic benefits**

Metabolic syndrome or insulin resistance is the co-existence of risk factors for cardiovascular diseases and type 2 diabetes mellitus (T2DM) including hypertension, central obesity, high blood glucose level and dyslipidemia. Bariatric surgery is by far the most effective treatment for metabolic syndrome. The effects of bariatric surgery on each component of metabolic syndrome are discussed below.

#### *2.2.1 Effects on type 2 diabetes mellitus*

Durable remission of T2DM is reported in 23 to 60% of cases [15]. Glycemic control improves within days after the surgery suggesting the role of weight loss independent factors. Bariatric surgery influences β-cell function, incretin responses, insulin sensitivity, gut microbiota, bile composition, intestinal glucose metabolism and brown adipose tissue metabolism [16, 17]. Weight loss contributes to better glycemic control in the long run. A French national survey study demonstrated the preventative role of bariatric surgery in T2DM [18]. The risk of developing T2DM was lower in the surgery group than medical therapy group [2 vs. 13% hazard ratio (H.R.) 0.18, 95% CI: 0.17–0.19]. Roux en Y gastric bypass and SG conferred better protection against T2DM than AGB (1.2 vs. 0.9 vs. 4.5%, respectively). Patients with a shorter duration of T2DM, better pre-operation glycemic control and significant weight loss post-surgery had higher chances of achieving remission.

Many prospective and retrospective studies have shown favorable effects of bariatric surgery on the management of T2DM. A meta-analysis [19] reported higher rates of T2DM remission with RYGB than medical therapy at 1 year [RR, 18.01; 95% CI: 4.53–71.70], 3 years (RR, 29.58; 95% CI: 5.92–147.82) and 5 years (RR, 16.92; 95% CI: 4.15–69.00). Moreover, a higher proportion of patients in the RYGB group achieved the American Diabetes Association (ADA) treatment targets at 1, 2, 3 & 5 yr.

Another meta-analysis [20] comprising mainly of observational studies reported a T2DM remission rate of 78% and an improvement rate of 87% at 1–3 years follow-up.

A prospective multi-center study [21] compared SG to RYGB and AGB. Type 2 diabetes mellitus improved or remitted in 83, 55 and 44% with RYGB, SG & AGB respectively at 1 year.

Most observational studies show better remission rates of T2DM with RYGB than SG. However, prospective studies demonstrate comparable efficacy of RYGB and SG inducing T2DM remission [8, 22]. The effectiveness of AGB is low in this regard.

Remission of T2DM induced by bariatric surgery is more durable than medical management. A French population-based cohort study illustrated that a greater proportion of patients in the surgery group (RYGB, SG & AGB) were able to discontinue antidiabetic medications at 6 years than medical therapy alone (−49.9% vs. −9.0%, P < .001) [23]. Roux-en-Y gastric bypass surgery was more effective in discontinuation of antidiabetic medication than SG and AGB.

A single center study [24] randomly assigned 150 obese participants with uncontrolled T2DM were assigned to either intensive medical therapy alone or medical therapy + RYGB or SG. The primary endpoint was lowering HbA1c to <6% at 12 months. More patients in RYGB and SG groups achieved the primary endpoint than medical therapy alone (42, 37 and 12%, respectively).

Another study randomly assigned obese patients with poorly controlled T2DM to medical therapy alone or RYGB or biliary pancreatic diversion (BPD) [25]. The primary aim was remission of T2DM (fasting blood glucose <5.6 mmol/l and HbA1c < 6.5% without medication) was achieved by 0, 75 and 95% of participants with medical therapy alone, RYGB and BPD, respectively. Type 2 diabetes mellitus remained in remission at 10 years in 5.5, 25 and 50% with medical treatment alone, RYGB and BPD, respectively.
