*2.2.2 Effects on diabetic mellitus complications*

Several retrospective studies illustrate the beneficial effects of bariatric surgery on macrovascular and microvascular complications of T2DM.

A retrospective study reported lower composite macrovascular events in the surgery group than in the medical therapy group [2.1 vs. 4.3%, HR 0.60 (95% CI: 0.42–0.86)] at median 5 years follow-up [26].

Another large retrospective study [27] looked at the extended major adverse cardiovascular event (MACE) in diabetic obese individuals who underwent bariatric surgery or medical therapy. At 8 years, the cumulative incidence of MACE was 30.8% (95% CI: 27.6%–34.0%) in the surgical group vs. 47.7% (95% CI: 46.1%–49.2%) in medical treatment group.

A meta-analysis [28] of 19 studies concluded lower mortality [OR 0.34; 95% CI: (0.25–0.46)] and T2DM macrovascular complications [OR 0.38, (95% CI: 0.22–0.67)] with bariatric surgery compared to medical treatment.

A large cohort study [29] reported a lower incidence of microvascular complications in patients who had bariatric surgery than medical treatment at a median followup of 4.3 years [16.9 vs. 34.7% HR 0.41 (95% CI: 0.29–0.58)]. Diabetic neuropathy improved the most among microvascular complications [7.2 vs. 21.4% HR, 0.37 (95% CI: 0.30–0.47)].

In summary, bariatric surgery plus medical therapy induces sustainable remission of T2DM in a significant proportion of patients than medical therapy alone. Bariatric surgery also has favorable effects on the complications of T2DM. Remission of T2DM has a 'legacy effect' or 'metabolic memory' [30], which protects against microvascular complications even after relapse of T2DM.

Most of the guidelines recommend bariatric surgery for patients with class III obesity (BMI ≥ 40 kg/m<sup>2</sup> ) or class II obesity (BMI 35–39.9 kg/m<sup>2</sup> ) with significant comorbidities. However, clinicians have a growing consensus to consider bariatric surgery for uncontrolled T2DM with medical therapy even with less severe obesity. Bariatric surgery with the primary intent to treat the metabolic syndrome of T2DM is called metabolic surgery. The Diabetes Surgery Summit

(DSS-II) consensus conference guidelines [31] recommend metabolic surgery for patients with poorly controlled T2DM with oral or injectable treatments and class I obesity [BMI 30–34.9 kg/m<sup>2</sup> (27.5–32.4 kg/m<sup>2</sup> for the Asian population)]. DSS-II recommendations are endorsed by American Diabetes Association and many other organizations [32].

#### *2.2.3 Hypertension (HTN)*

Hypertension improves with weight loss. The role of bariatric surgery in managing HTN was best demonstrated by the Gastric bypass to treat obese patients with steady hypertension (GATWAY) trial [33]. The study population randomly received medical therapy alone or RYGB + medical therapy. The primary aim was to reduce antihypertensives by ≥30% compared to baseline. More patients in RYGB + medical therapy group achieved the primary endpoint than medical therapy alone at 1 year (84 vs. 13%) and 5 years (73 vs. 11%). A significant proportion of patients in the RYGB group achieved remission of HTN at 1 (46 to 0%) and 5 years (31 to 2%) compared to medical therapy. Moreover, variability in ambulatory blood pressure was low in the RYGB group compared to medical treatment.

A Norwegian cohort study reported HTN remission in 31.9% of individuals who underwent bariatric surgery + medical therapy versus 12.4% in the medical treatment alone group at 6.5 years [34].

What surgical procedure is more efficacious in inducing HTN remission is not clear [21, 35].
