in 2005 the international association for the study of obesity reported that the prevalence of obesity , defined by bmi  30  kg / m is more than 20% in many european countries . future obesity for adults in the united states was projected on the basis of national health and nutrition examination study . by 2030 , 86.3% american adults will be overweight or obese ; 51.1% of them will be obese . total health - care costs attributable to obesity / overweight would double every decade to 2030 , accounting for 1618% of total us health - care costs . in china , a fast developing country , the prevalence of overweight and obesity in 2008 in chinese population aged 20 years or older reached 24.9% , 4.9% in women and 30.8% and 6.0% in men , respectively . timely and effective development and implementation of corrective approaches are needed to avoid the catastrophic health and social consequences . obesity is associated with a cluster of metabolic risk factors for coronary heart disease ( chd ) , known as metabolic syndrome . abdominal obesity is an essential component of this syndrome , other components include impaired glucose regulation and type 2 diabetes mellitus ; hypertriglyceridemia and/or low serum hdl - cholesterol levels ; hypertension . in addition , increased serum levels of c - reactive protein ; apolipoprotein b ; small , dense ldl particles are also associated with abdominal obesity [ 4 , 5 ] . the drastic increase in the prevalence of obesity has played an important role in the spread of diabetes not only in the united states [ 6 , 7 ] , but also in china . the prevalence of diabetes increases from 12.8% in those with a bmi of 25.0 to 29.9 this increase even occurs in rather lean population in chinese , that is , the prevalence of diabetes increased from 4.5% in those with a bmi < 18.5 kg / m to 7.6% in those with a bmi of 18.5 to 24.9  kg / m . the association of hypertension and obesity has been described elsewhere [ 3 , 912 ] . consequently , the increase of bmi is associated with the increased cardiovascular diseases ( cvd ) . for instance , the average bmi in patients with stroke is 25.5  kg / m , compared with 23.7  kg / m in those without cvd in chinese . the risk of fatal and nonfatal myocardial infarction and ischemic stroke increases consistently with increasing bmi in other population [ 13 , 14 ] . the pickwickian syndrome is a severe form of the obesity - hypoventilation syndrome , involveing extreme obesity , irregular breathing , somnolence , cyanosis , secondary polycythemia , and right ventricular dysfunction . obesity is associated with nonalcoholic fatty liver disease ( nafld ) that encompasses a spectrum ranging from simple steatosis to nonalcoholic steatohepatitis ( nash ) , fibrosis , and cirrhosis . most of the available data suggests that steatosis affects approximately 75% , steatohepatitis approximately 20% , and cirrhosis approximately 2% of obese patients [ 1820 ] . a prospective study in more than 900,000 us adults , shows overweight and obesity could account for 14% of all deaths from cancer in men and 20% of deaths in women . a meta - analysis of 282,137 incident cases , demonstrated that in men , a 5  kg / m increase in bmi was strongly associated with oesophageal adenocarcinoma and with thyroid , colon , and renal cancers . in women , strong associations between a 5  kg / m increase in bmi and endometrial , gallbladder , esophageal adenocarcinoma , and renal cancers were recorded . a stronger association in asia - pacific populations between increased bmi and premenopausal and postmenopausal breast cancers was recorded . moreover , the risk of osteoarthritis of weight - bearing joints is increased in overweight and obese persons and the knees were most often involved . compared with general obesity , abdominal obesity seemed to be more harmful than general obesity . the risk of diabetes increases with increases in abdominal fat mass , waist circumference , or waist - to - hip circumference ratio independent of bmi value [ 24 , 25 ] . excess body fat deposited viscerally rather than elsewhere in the body is associated with higher risk for hypertension . abdominal fat mass is a risk factor for stroke independent of bmi , but not independent of diabetes , smoking , and hypertension . although a great progress has been achieved in the study of mechanism underlying chronic complications in obesity , we are yet to clarify the specific mechanism . insulin resistance is hypothesized to be the common underlying pathogenic mechanism of metabolic syndrome . the ectopic accumulation of triglycerides in nonadipose tissue may be involved in the pathogenesis of insulin resistance . however , according to data obtained from nondiabetic subjects in the framingham offspring study , insulin resistance might not be the only precedent condition in metabolic syndrome , other independent physiologic process may be involved . for instance , ikk/nf-b in the mediobasal hypothalamus  in particular in the hypothalamic pomc neurons may represent a primary pathogenic link between obesity and hypertension . weight loss has been proved to be an essential for the prevention , and treatment for obesity - related chronic diseases . sustained modest weight loss among obese persons would yield substantial benefit , reducing the lost number of years of life with hypertension , hypercholesterolemia , type 2 diabetes and the expected lifetime incidence of chd and stroke [ 32 , 33 ] . modest weight loss over short - term ( 6 weeks ) and longer - term ( 612 months ) periods is associated with reduction in subsequent cardiovascular mortality for the following 4 - 5 years even in those with preexisting cardiovascular disease . in morbidly obese subjects , bariatric surgery effectively induces weight loss and improvement in sleep - disordered breathing severity and symptoms . weight loss program also reported to have resulted in a highly significant improvement in symptoms in overweight patients with knee osteoarthritis . weight loss may not be a desirable for patients with cancer , however , it improved quality of life in breast cancer survivors . systematically review of 78 randomized trials has shown that lifestyle - induced weight loss was safe intervention for nafld , and that a weight loss 7% improved histological disease activity , but was achieved by < 50% patients . nevertheless , we should be aware of the side effect of weight loss . the risk of gallstones increases during weight loss , particularly when weight loss is rapid . this increased risk is related to increased bile cholesterol supersaturation , enhanced cholesterol crystal nucleation , and decreased gallbladder contractility . in a small 6-month study , asymptomatic gallstones developed in 6/11 of subjects following the lower fat diet , but in none with the higher fat regimen . a daily dose of 500  mg of ursodeoxycholic acid for 6 months is effective prophylaxis for gallstone formation following gastric restrictive procedures . currently available weight - loss treatments include dietary intervention , increased physical activity , behavior modification , pharmacotherapy , and surgery . in china , acupuncture has been applied in the treatment of obesity , but no well - designed clinical trial has been reported . negative energy balance is more readily achieved by decreasing food intake than by increasing physical activity for most obese people . many obese persons can achieve short - term weight loss by diet alone , but successful long - term weight maintenance is much more difficult . however , dietary intervention is still considered as the cornerstone of weight - loss therapy . low - calorie diets ( lcds ) contain 800 to 1500  kcal / day and are consumed as liquid formula , nutritional bars , conventional food , or a combination of these items . very - low - calorie diets ( vlcds ) contain less than 800  kcal / day and are generally high in protein ( 70100  g / day ) and low in fat ( < 15  g / day ) . the nih guidelines recommend a more aggressive energy deficit of 500 to 1000  kcal / day for persons with more severe obesity ( bmi  35.0  kg / m ) . individuals intended to reduce body weight should continue to be advised on regularly self - monitoring of energy intake and expenditure as well as creating a consistent daily energy deficit . low - fat diets have traditionally been prescribed for weight loss because such diets facilitate energy restriction , due to their low energy density . low - carbohydrate diets have been evaluated as a potential therapy for obesity in rcts . the mechanism responsible for the decrease in body weight associated with a low - carbohydrate diet can be completely explained by a decrease in total energy intake . however , moderate endurance exercise , such as brisk walking for 45 to 60 minutes , 4 times a week , usually induces only minor weight loss in 1 year . although exercise alone is not an effective strategy for inducing initial weight loss , increasing physical activity is an important component of successful long - term weight management . fat - free mass ( ffm ) represents a key determinant of the magnitude of resting metabolic rate ( rmr ) , which follows a decrease in lean tissue could hinder the progress of weight loss . weight - loss maintenance requires expending approximately 2500  kcal / wk during exercise [ 45 , 46 ] . this level of energy expenditure can be accomplished through vigorous activity ( aerobics , cycling , or jogging ) for approximately 30 min / day or more moderate activity for 60 to 75  min / day . behavior modification for the treatment of obesity is perhaps the most important but difficult approach . these strategies include : eating stimulus control , self - monitoring , problem - solving skills , cognitive restructuring , social support , and relapse prevention . treatment by an enhanced brief lifestyle counseling ( including medications ) in primary care results in about a 4.6  kg in 2-year trials . unfortunately , orlistat is only available medicine for long - term therapy , but the efficacy is limited [ 48 , 49 ] . pharmacotherapy alone is less successful than being part of a comprehensive weight - loss program that includes diet , exercise , and behavior modification . benzphetamine hcl , phendimetrazine tartrate , phentermine , diethylpropion hydrochloride , mazindol , and orlistat are the drugs currently approved by the us food and drug administration for the treatment of obesity . all currently approved weight - loss drugs act as anorexiants , with the exception of orlistat . anorexiants affect the monoamine system in the hypothalamus and thereby enhance satiety . in the last several years , fenfluramine , phenylpropanolamine , sibutramine , and dexfenfluramine were withdrawn from the market because of the increased incidence of either valvular heart disease or cardiovascular diseases / stroke associated with their use [ 51 , 52 ] . all anorexiant drugs , except mazindol , are derived from -phenylethylamine , the amphetamine precursor . the structures of these drugs have been chemically altered to reduce the potential for abuse . even though , these anorexiant medications are strictly regulated for short - term therapy . a low - dose anorexiant has been test for long - term therapy . in a phase 3 extension study , a controlled release of phentermine / topiramate ( an anticonvulsant ) in conjunction with lifestyle modification resulted in up to 10.5% weight - loss for 108 weeks and is well - tolerated . orlistat works by binding to lipases in the gastrointestinal tract and blocks the digestion of dietary triglycerides . this inhibition of fat digestion reduces micelle formation and , subsequently , reduces the absorption of long - chain fatty acids , cholesterol , and certain fat - soluble vitamins . excretion of about 30% of ingested triglycerides , which is near the maximum value , occurs at a dose of 360 mg / day ( 120  mg t.i.d with meals ) . orlistat has no effect on systemic lipases because less than 1% of the administered dose is absorbed . serious liver injury events including liver failure in patients using orlistat were collected by fda 's adverse event reporting system . the most commonly reported adverse events of serious liver injury were jaundice , weakness , and abdominal pain . even though no definite association between liver injury and orlistat has been established , fda urges both healthcare professionals and consumers to report side effects from the use of orlistat . metformin has shown its efficacy for weight loss in obese patients with type 2 diabetes . glp-1 analogs or glp-1 receptor agonists used in type 2 diabetic patients also demonstrated a weight loss effect . therefore , they could be potential medications to treat obesity or an approach for weight loss . theoretically , fat loss could also be achieved through a decrease in the size and number of adipocytes through apoptosis , so that targeting adipocyte apoptosis could be a novel strategy for obesity therapy . bariatric surgery is a safe and effective treatment for morbid obesity and related metabolic diseases . it can be categorized as those that primarily cause gastric restriction and those that primarily cause biliopancreatic bypass , subsequently , nutrient maldigestion and malabsorption [ 5060 ] . perioperative mortality rate after bariatric surgery is less than 0.5% when the procedure is performed by experienced surgeons in experienced centers [ 6163 ] . among them , three - fourths of the deaths are due to anastomotic leaks and peritonitis and one - fourth are due to pulmonary embolism . laparoscopic surgery may be a safer treatment than open surgery . compared with open surgery , laparoscopic surgery is associated with lower risk of wound infection and incisional hernia . as an elective procedure , bariatric surgery should be carefully selected , extensively evaluated , and optimized in order to achieve optimal outcomes . in 1991 , guidelines for the surgical treatment of obesity were established by an nih consensus conference , since then these guidelines had hardly been changed [ 64 , 65 ] . according to these guidelines , eligible candidates for surgery include patients with a bmi 40  kg / m or more or those with a bmi of 35.0 to 39.9  kg / m and one or more severe medical complications of obesity .   in summary , obesity becomes a world - wide epidemic , the chronic complications result in huge burdens for the patients , family , and society . although progresses have been made in the management of obesity , an effective safe intervention remains to be developed .
the prevalence of obesity is more than 20% in many developed countries and it increases in developing countries . 
 obesity is associated with metabolic disorders , cardiovascular diseases , pulmonary diseases , digestive diseases , and cancers . 
 although other specific treatments for these complications exist , weight loss is still an essential intervention in obesity and its complications . 
 therapeutic life change , behavior modification , pharmacotherapy , and surgery are major approaches to weight loss . 
 in addition , medicine used in diabetes such as glucagon - like peptide-1 analogues may be a new type of medicine for obesity , at least for those obese patients with diabetes .