The prevalence of both obesity and asthma is increasing and appears at least in part associated. Obesity has become an established risk factor for asthma in both children and adults. Asthma may be missed in the context of shortness of breath with severe obesity, and asthma is often difficult to control in obese patients, especially younger women. The pulmonary physiological changes associated with obesity aggravate the airway obstruction that occurs with asthma. Other comorbidities of obesity including gastroesophageal reflux, obstructive sleep apnea, and the low-grade inflammatory state of obesity may contribute to asthma risk and difficulty in achieving control.

Multiple observational studies have consistently reported major improvements and even remission of asthma following bariatric surgery. These changes have included fewer attacks, less use of medications, fewer hospital admissions, lower daily impact, less exercise-induced asthma, and improved sleep. However, most studies have not adequately characterized or adequately diagnosed the asthma at baseline. More recently, airway hyperresponsiveness to methacholine challenge has been shown to improve following surgery in those with non-atopic asthma. This change, however, was not associated with a reduction in CD4 lymphocyte airway inflammatory markers, but rather an increase [1]. Improvements to lung function, gastroesophageal reflux, and sleep apnea with weight loss may also reduce breathlessness and asthma symptoms. Further studies are needed to clarify the nature of the relationship between obesity and asthma, to identify those most likely to respond to weight loss, and to formally test the effect of bariatric surgery on asthma in randomized controlled trials.

Increasing body mass index (BMI) is strongly associated with a large range of malignancies in men and women. In men, cancers strongly associated with increasing BMI include esophageal adenocarcinoma, thyroid, colon, and renal cancer. In women, strong associations include endometrial, gallbladder, esophageal adenocarcinoma, and renal cancers. There are weaker associations with a large range of other cancers including pancreatic, postmenopausal breast cancer, leukemia, myeloma, non-Hodgkin lymphoma, and malignant melanoma [2].

Several studies, including the Swedish Obese Subjects Study, have now demonstrated a reduction in cancer deaths in women who have had bariatric surgery [3]. These findings are an exciting development and suggest that substantial weight loss can reduce the development and the progression of some cancers.

Raised intra-abdominal pressure and pelvic fat distribution may alter urodynamic mechanisms, predisposing to stress incontinence in women. Obese women with stress urinary incontinence were found to have very high urinary bladder pressures that normalized following bariatric surgery. High intra-abdominal pressure is thought to produce a chronic abdominal compartment syndrome [4]. Relatively small rises in intra-abdominal pressure have a profound effect on venous function, including venous pressure, compliance, distension, and blood flow. Raised intra-abdominal pressure will reduce lower limb venous return and increase pressure, therefore causing edema and predisposing to venous stasis, ischemia, and ulcers. Renal vein compression and ischemia may predispose to activation of the renin–angiotensin system, hypertension, and proteinuria. Raised intra-abdominal pressure also reduces cardiac output, increases peripheral resistance, and increases intrathoracic pressure and intracranial pressure. Thus, comorbidity hypothesized to be related at least in part to raised intra-abdominal pressure includes cardiac failure, obesity hypoventilation syndrome, venous stasis disease including stasis ulcers, gastroesophageal reflux disease, urinary stress incontinence, incisional hernia, pseudotumor cerebri, proteinuria, and systemic hypertension. Chronic raised abdominal compartment syndrome provides a good example of how physical pressure generated by excessive abdominal obesity can generate profound metabolic and vascular changes (Fig. 33.2).

Weight loss following bariatric surgery reduces stress urinary incontinence, chronic venous stasis, peripheral bronzed edema, and cellulitis and provides conditions conducive to the healing of venous ulcers. Bariatric surgery is the treatment of choice for obese patients with pseudotumor cerebri [5], and several recent observational studies have shown that chronic headaches often improve or resolve completely following substantial weight loss [6].

Obesity is regarded as an important contributing factor to gastroesophageal reflux disease (GERD), and study of symptom frequency in obese groups indicates prevalence of between 37 and 72 %. The increased risk in severely obese patients has been confirmed with 24-h pH monitoring and is associated with reduced lower esophageal pressure, together with raised intra-abdominal pressure, as discussed previously. Bariatric surgeons report finding a high prevalence (approximately 30 %) of hiatal hernia in patients at the time of bariatric surgery that requires exploration and repair concurrent with primary bariatric surgery.

It is broadly assumed that weight loss will help alleviate the symptoms of gastroesophageal reflux, and advice regarding weight loss has become a standard part of the clinical management of these patients. It is only recently, however, that the HUNT study, a large population study performed in Norway, has confirmed a dose-dependent relationship between weight loss and reductions in GERD symptoms and medication requirements.

Bariatric surgery confounds the effect of weight loss on GERD as the majority of procedures involve the area in the region of the gastroesophageal junction. Roux-en-Y gastric bypass (RYGB) or a correctly placed and adjusted laparoscopic adjustable gastric band (LAGB) usually produces an immediate reduction or abolition of reflux symptoms due to the anatomical arrangement generated by the surgery. In grade II and III obese patients presenting for anti-reflux surgery, using one of these options may provide a better solution for the patient’s condition than a stand-alone anti-reflux procedure. The picture is currently unclear for sleeve gastrectomy (SG), and many regard significant GERD to be a contraindication to SG. However, this procedure is still in the process of refinement and newer techniques may reduce reflux symptoms. Complications altering the anatomy of all bariatric procedures (RYGB, LAGB, and SG—especially the latter two) can lead to reflux symptoms that warrant investigation. A form of gastric bypass—the mini or loop gastric bypass (MGB)—is specifically associated with reflux symptoms, and there is a high risk of bile reflux.

The risk of developing gallstones increases with increasing levels of obesity, with a relative risk of 5–6 with a BMI > 40 kg/m². Obesity is a risk factor for all age groups in both men and women. Stone development appears to be more related to the level of obesity rather than the level of metabolic disturbance. This increased prevalence is mostly attributable to supersaturation of the bile with cholesterol as a result of increased hepatic cholesterol synthesis and secretion into the bile. The increased risk of developing gallstones is associated with the increased risk of complications including biliary colic, cholecystitis, biliary obstruction, and pancreatitis. The complication of gallstones including pancreatitis may be more serious, and gallstones are a likely cause of the increased risk of gallbladder carcinoma in obese subjects.

The development of symptomatic gallstones increases with weight loss, especially with weekly weight loss in excess of 1.5 kg (3.3 lb), with low-fat low-calorie diets, and with bariatric surgery when the duodenum is bypassed [7]. Screening for gallstones, prophylactic cholecystectomy at the time of surgery, and the use of ursodeoxycholic acid to reduce the risk of gallstones during rapid weight loss are all options to mitigate risk in procedures with a high risk of gallstone development.

Hypertension is the most common comorbidity of obesity, but the major mechanisms driving an increase in blood pressure (BP) in the obese are not known [8]. The effect of increasing levels of body mass index and weight gain on the prevalence of hypertension is clearly established, but the effect of intentional weight loss, especially with bariatric surgery, on blood pressure levels is not. In addition, therapy for hypertension in obese patients is problematic, often requiring multidrug therapy, and obese patients are over represented in those presenting with resistant hypertension [8]. Worldwide, hypertension is the leading risk factor for mortality and is ranked third as a cause of disability-adjusted life years. Hypertension is one of the most important risk factors for a broad range of health issues and target organ damage including stroke, heart failure, coronary artery disease, left ventricular hypertrophy, renal failure, and diabetes-associated complications. It is the most common condition treated by primary care physicians.

The pathophysiology of obesity-related hypertension has several putative mechanisms with complex interrelationships. Fundamental mechanisms involve hemodynamic alterations, impaired endothelial function, activation of the renin–angiotensin system, and activation of the sympathetic nervous system. Our literature review of antihypertensive effect of weight loss on blood pressure found the following: short- and medium-term weight loss (3–9 %) using lifestyle measures provides modest reductions in BP; the effect is reduced by weight regain; and bariatric surgery, while producing excellent sustained weight loss, provides a modest mean reduction in BP, suggesting a nonlinear relationship. There is an interesting contrast between the bariatric observational literature, which generally reports resolution, improvement, or no change, and the high-quality bariatric surgical literature. The Swedish Obese Subjects study found that, while the surgical group had much greater sustained weight loss compared with controls, remission of hypertension and incident hypertension were similar in each group. In addition, none of the recent randomized controlled trials comparing bariatric surgery to conventional weight loss therapy have reported a lower mean pressure in the surgical compared with control groups. There were falls in both systolic and diastolic blood pressure in the studies, but a nonlinear association with weight loss. While less frequent medication use is reported in some studies, inappropriate cessation of medications may leave patients at risk, so such findings must be interpreted with caution. These findings contrast with the 62 % resolution of hypertension reported in the Buchwald et al., 2004, meta-analysis [9]. Recently, it has been shown that sympathetic nervous system activity and plasma renin activity fall during active weight loss but rise again during a period of sustained weight loss. The effect of intentional weight loss, including that associated with bariatric surgery, on hypertension is unpredictable, incomplete, and may be temporary.