The Korean Society for the Study of Obesity (KSSO) published a 2019 Obesity Fact Sheet based on data from the Korean National Health Insurance Service, which stated that the prevalence of obesity in Korea increased from 29.7% in 2010 to 35.7% in 2018. The prevalence of abdominal obesity among Korean adults in 2018 was 23.8% (28.1% for men and 18.2% for women), indicating a steady increase from 19.0% in 2009.¹ Obesity is associated with metabolic abnormalities such as type 2 diabetes, dyslipidemia, insulin resistance, metabolic syndrome, gallbladder disease, coronary artery disease, hypertension, and cancer. There is an increased risk of comorbidities (directly linked with obesity) such as arthritis, back pain, and sleep apnea. Therefore, obesity is associated with medical and socio-economic burdens due to comorbidities. In addition, the treatment and management of obesity is changing, reflecting new clinical evidence.

The revised 2020 Obesity Treatment Guidelines (7th edition) was based on the previous 2018 Obesity Treatment Guidelines (6th edition),² and included the latest research results. Levels of evidence and a variety of clinical situations were taken into account when formulating the recommended grades. In addition, changes and developments in the 2019 anti-obesity drug market were reflected in the revised guidelines.

This treatment guideline was organized into questions divided into nine major topics with the goal of increasing utilization in clinical practice among primary care physicians treating obese patients. The new revised guidelines summarize evidence-based recommendations and treatment guidelines. The levels of evidence were classified into A, B, C, and D (Table 1). The standards of the recommended grade were presented using a modified Grading of Recommendation Assessments, Development and Evaluation (GRADE) method³ and the grades were divided into classes I, IIa, IIb, and III. Recommendations with low levels of evidence, but clear benefits or high utilization rates in treatment according to user opinion survey results, were partially upgraded with the agreement of the treatment guidelines committee. In order to determine the strengths of recommendations, factors such as the level of evidence, the level of use at primary care sites reflecting benefits and risks, practicability, and acceptance were comprehensively considered (Table 1).

In this article, we introduce and briefly describe the 2020 Korean Society for the Study of Obesity (KSSO) Guideline for the Management of Obesity in Korea.

This clinical practice guideline informs the arc of the patient journey and the approach for clinical management of obesity in the primary care setting. The guideline recommendations are shown in Table 2 and include nine major themes: evaluation before obesity treatment, behavioral therapy, physical activity, nutrition therapy, pharmacotherapy, bariatric surgery, obesity in the elderly, obesity in children and adolescents, and metabolic syndrome. The purpose of the guideline is as follows. First, it helps practitioners, who are the main users of the guideline, to make safer and more effective decisions by providing evidence-based recommendations with clear evidence levels and benefits. Second, it provides high-quality evidence-based information for primary care physicians.

Diagnosis of obesity is important in the evaluation stage before obesity treatment. Body mass index (BMI), which is a value obtained by dividing body weight (kg) by the square of height (m²), is highly correlated with body fat mass, and because BMI can be used to evaluate health risks such as morbidity and mortality of obesity-associated diseases, BMI is the most commonly used index to diagnose obesity. The World Health Organization (WHO) defines obesity as BMI ≥30 kg/m². However, East Asians, including Koreans, have increased risk of diabetes and cardiovascular disease even below BMI of 25 kg/m² and higher abdominal fat and body fat percentages than Westerners at the same BMI.⁴ There is concern that the general WHO definition of obesity underestimates health risks associated with obesity in East Asians. The classification of obesity into classes I, II, and III relies on adult BMI in accordance with WHO guidelines for the Asia-Pacific region.⁵ Class I obesity is defined as BMI 25.0 to 29.9 kg/m², class II obesity is defined as BMI 30.0 to 34.9 kg/m², and class III obesity was newly defined in 2018 as ≥35.0 kg/m² (Table 3).

Waist circumference (WC) is highly associated with intra-abdominal fat.⁶ WC is measured in the horizontal plane midway between the superior iliac crest and the lower margin of the last rib.⁷ According to the KSSO, abdominal obesity in Koreans is defined as WC ≥90 cm in men and ≥85 cm in women (Table 3). In the case of abdominal obesity, the morbidity and mortality of metabolic syndrome, diabetes, and coronary artery disease increase independently of BMI, so it is necessary to increase the risk of comorbidities classified by BMI to the next level (Table 3).

In some obese patients, secondary obesity is caused by genetic and congenital disorders, drugs, neurological and endocrine disorders, and psychiatric disorders.⁸ In patients with secondary obesity, relatively effective weight loss can be expected after accurate identification of the cause, so discerning secondary obesity is very important. Obesity causes metabolic abnormalities as well, and even if metabolic abnormalities are not present, obesity itself causes complications. Therefore, it is necessary to evaluate the comorbidities of obesity when treating obese patients.

To lose weight, it is necessary to reduce energy intake. Many weight control programs prescribe low-calorie diets that reduce energy intake by 500–1,000 kcal, in which case a weight loss effect of 0.5–1.0 kg per week is expected.⁹ Therefore, based on the results of several studies, a low-calorie diet that reduces energy intake by 500–1,000 kcal per day can bring about weight loss without negative health effects and is also relatively easy to follow. Limiting total energy intake is important for the treatment of obesity, but there is a continuing interest in the effects of dietary macronutrients, especially carbohydrate composition, on weight loss. In the early 2000s, some randomized controlled studies reported that low-carb diets resulted in greater initial weight loss than traditionally recommended low-fat diets.¹⁰ The definition of a low-carbohydrate diet is not clear and varies according to researchers, but diets with daily carbohydrate intake of more than 130 g and less than 45% of total energy are classified as low-carbohydrate diets, while diets with a daily carbohydrate intake of less than 130 g are sometimes classified as very-low carbohydrate diets.¹¹ Several studies indicated that low carbohydrate diets resulted in significantly greater weight loss during the initial 6 months compared to control diets.^10,12,13 This difference from the control group persisted at 1 year, but compared to the initial 6 months, the difference was reduced.^14-16

Increasing total fat intake through a very-low carbohydrate diet is likely to be accompanied by increased intake of saturated fatty acids and trans-fatty acids, and several studies report that such intake has negative effects on vasodilating capacity at the initiation of very-low carb diets.^17-19 Adhering to a low-carb diet can be considered a method of weight loss, but is not effective in the long term and may negatively affect cardiovascular health, so it is necessary to pay special attention to fatty acid composition.

Consistently limiting energy intake can help in losing weight, but many individuals find it difficult to follow a strict energy-restricted diet.¹⁹ Interest in intermittent fasting as an alternative to sustained energy-restricted diets has increased. Intermittent fasting has many forms. Meta-analyses of intermittent fasting and time-limited diets suggest that these dietary methods can result in levels of weight loss effect equivalent to those accomplished via continuous energy-restricted diet, but related studies, especially regarding long-term effects, are insufficient. There is limited evidence to include intermittent fasting as a method of dietary treatment, and further studies are needed. The KSSO guidelines summarize the characteristics of each dietary treatment.²⁰

Exercise and physical activity are important factors in lifestyle interventions for weight loss. The weight loss effect of exercise rarely exceeds 5%, but exercise and physical activity reduce the risks associated with various metabolic factors such as weight, body fat percentage, and visceral fat, and improves lean mass and functional ability.^21,22 In addition, exercise with nutrition therapy has been found to be more effective than nutrition therapy alone, or exercise without nutrition therapy.²³

In individuals with no cardiovascular, metabolic, or kidney disease, and no signs or symptoms, there is no need for medical permission before prescribing exercise for either regular exercise participants or non-participants.²⁴ In accordance with the exercise guidelines, non-participants in regular exercise can start with low and moderate intensity exercise, while regular exercise participants may begin with moderate and high intensity exercise and gradually increase exercise intensity. Regular exercise participants with underlying cardiovascular (heart, peripheral artery, or cerebrovascular) disease, metabolic disease (type 1 or type 2 diabetes), or kidney disease, but who are asymptomatic, do not need medical permission to engage in moderate intensity exercise. Medical permission is recommended prior to high-intensity exercise.²⁴

Aerobic exercise is an essential tool in weight loss programs addressing obesity. It is recommended to perform moderate-intensity exercise at least 150 minutes per week, 3–5 times a week, starting with low-intensity exercise and gradually increasing the intensity and amount of exercise according to individual fitness level. Resistance training should be prescribed in a weight loss exercise program to increase lean mass and promote body fat loss, and it is recommended to perform exercise using large muscle groups 2–4 times a week.²⁵

Behavior therapy can be applied not only as a programmed behavior intervention for weight control, but also for the purpose of changing behaviors related to food intake and physical activity. Treating obesity has long been known to be more effective when lifestyle interventions including behavioral therapy are performed. Therefore, all obese people should undergo behavioral therapy, along with nutrition therapy and increased physical activity. Specific methods used in behavioral therapy include self-monitoring, reinforcement, stimulus control, alternative behavior, and cognitive reconstruction.

When treating obesity, it is very important to diagnose and treat any eating disorders that may exist. Eating disorders should be considered when binge eating, weight control behaviors to offset the effects of binge eating, and excessive emphasis on weight or body shape are observed in obese people. Obese people with eating disorders benefit from psychological therapies such as guided self-help or cognitive behavior therapy focused on eating disorders.²⁶

When treating obesity, smoking and alcohol consumption must be reduced. Obese people should be advised to quit smoking.²⁷ Alcohol has a high caloric content of about 7.1 kcal per gram, and the liver produces fat in trace amounts.^28,29 In addition, most ingested alcohol is converted to acetate, which interferes with peripheral fat breakdown and utilization. Clinically, alcohol raises blood pressure, and excessive drinking increases the risk of hypertriglyceridemia, insulin resistance, type 2 diabetes, metabolic syndrome, and abdominal obesity. Therefore, controlling excessive drinking is important for the prevention and control of obesity and metabolic syndrome.³⁰

The basic treatments for obesity are nutrition therapy, physical activity, and behavior therapy. We recommend pharmacotherapy as an additional treatment alongside comprehensive lifestyle intervention. According to the KSSO guideline, pharmacotherapy should be considered when non-pharmacotherapy-treated patients with BMI ≥25 kg/m² fail to lose weight (Fig. 1). Not all obese people respond to obesity drugs, and there are a significant number of non-responders. A commonly used criterion for predicting treatment response is weight loss of 5% or more within the initial 3 months. If there is no weight loss of more than 5% within 3 months of initiating the drug, pharmacotherapy should be changed or discontinued.

As of 2020, four types of obesity treatments have been approved for long-term administration in Korea: orlistat (Xenical), naltrexone-bupropion (Contrave), liraglutide (Saxenda), and phentermine-topiramate (Qsymia).³¹ These drugs have been approved for use in the treatment of obesity based on the results of clinical studies on long-term use. Lorcaserin (Belviq) was used as a treatment for obesity from February 2015 to February 2020, but due to increased risk of cancer, it was voluntarily withdrawn from the market in the Unites States and discontinued from sales in Korea.³² These four drugs induce significant weight loss when administered together with lifestyle modifications, and result in improvement and prevention of various complications. Anti-obesity drugs must be prescribed according to the characteristics of each patient, and the presence of other comorbidities is important when choosing drugs. Table 4 guides the selection of anti-obesity drugs according to comorbidities.

According to the International Federation for the Surgery of Obesity and Metabolic Disorders, Asian Pacific Chapter Consensus statements 2011(IFSO-APC consensus statements),³³ the indications of bariatric surgery are failure to lose weight due to nonsurgical treatment in patients with BMI ≥35 kg/m² or BMI ≥30 kg/m² and obesity-related comorbidities, and this indication is applied in Korea. In Korea, from January 2019, the national health insurance plan has covered bariatric surgery performed for the purpose of treatment in patients with severe obesity. In patients with BMI ≥35 kg/m² or BMI ≥30 kg/m² and obesity-related comorbidities, health insurance benefits are applied.

Types of bariatric surgery can be largely divided into restrictive surgery, malabsorptive surgery, and combined surgery. Restrictive surgeries include sleeve gastrectomy and adjustable gastric banding, and malabsorptive surgery is defined as biliopancreatic diversion/duodenal switch (Table 5). The typical combined surgery is Roux-en-Y gastric bypass, which results in both restriction and absorption inhibition (Table 5). These surgeries are standard procedures that have already proven their effectiveness and safety,³⁴ and since each surgical method has advantages and disadvantages, it is important to select an appropriate surgical method according to each patient’s situation. In addition, in order to secure the safety and efficiency of patient management before and after surgery, collaboration across various departments is essential.

Obesity in children and adolescents is rapidly increasing due to changes in diet, living environment, and decreases in physical activity. Obesity in children and adolescents is a chronic disease that is difficult to treat. It easily develops into adult obesity and requires a healthy diet and active lifestyle throughout life. Therefore, a policy of early detection and treatment should be established.

For the evaluation of obesity in children and adolescents, it is important to continuously evaluate obesity trends according to growth and development status through regular check-ups.³⁵ The most widely used indicator is BMI. Percentile of BMI by sex and age is used to evaluate obesity in children and adolescents aged 2 years or older. In addition, since the growth and development period and body composition may differ depending on ancestry, standard values for Korean children and adolescents are applied. Age is calculated in months.³⁵ Children or adolescents with BMI above the 85th percentile are considered overweight, those above the 95th percentile are obese, and those below the 85–95th percentile are regarded as pre-obesity.³⁵

Considering the effects of obesity and obesity treatment on growth and development, it is important to prepare a treatment strategy for maintaining appropriate weight and avoiding unconditional weight loss.^36-41 The key to the treatment of obesity in children and adolescents is to maintain an appropriate weight by inducing and continuing lifestyle modifications. Orlistat is the only drug approved by the U.S. Food and Drug Administration for usage by those over 12 years of age.^42,43

Body weight is gained naturally with age and in the elderly, mortality does not increase with BMI ≥25 kg/m². The mortality rate in the elderly population is influenced not only by weight but also by other variables such as comorbidities.⁴⁴ Therefore, for the diagnosis of obesity in the elderly, it is recommended to measure WC together with BMI, and indicators such as the WC to height ratio and the WC to hip circumference ratio can also be utilized.⁴⁵

Weight loss is recommended for elderly patients when it is judged that the benefits gained through weight loss during obesity treatment are greater than the harms. Even in the elderly, weight loss through lifestyle modifications such as diet control and physical activity is first considered and positive effects can be expected such as improving physical function and cardiovascular index.⁴⁶

Well-designed studies of the effectiveness and safety of anti-obesity medications in the elderly are insufficient. Among drugs for obesity treatment approved for long-term use, orlistat can be safely used for elderly patients.⁴⁷ Bariatric surgery in the elderly seems to be helpful for treating weight loss or diabetes,^48,49 but caution is necessary because the risk of complications after surgery may increase.⁵⁰

Metabolic syndrome is the term for a combination of metabolic abnormalities such as hyperglycemia, high blood pressure (hypertension) and obesity.⁵¹ Diagnosis criteria for metabolic syndrome are in the process of being integrated, as different organizations have different criteria. International Diabetes Federation criteria for diagnosing metabolic syndrome begin with the recognition of abdominal obesity as the most important etiology, and therefore, abdominal obesity is an essential requirement for diagnosing metabolic syndrome. In addition, one of the main features is that it is recommended to use WC measurements suitable for different groups in recognition that the diagnostic criteria for abdominal obesity may differ by ancestry. In 2007, based on the results of the National Health and Nutrition Survey, Korea recognized abdominal obesity when the WC was more than 90 cm for men and 85 cm for women,⁵² and a recent study found that this criterion was appropriate for Koreans. Diagnosis of metabolic syndrome in Korean adults requires ≥3 of the following five criteria: WC of ≥90 cm (men) or ≥85 cm (women), blood pressure ≥130/85 mmHg or taking anti-hypertensive medication, fasting blood glucose ≥100 mg/dL or taking anti-diabetic medication, triglycerides ≥150 mg/dL, and high-density lipoprotein cholesterol <40 mg/dL (men) or 50 mg/dL (women) or taking anti-dyslipidemia medication.

The goal of metabolic syndrome treatment is to prevent cardio-cerebrovascular diseases and diabetes. There are two major therapeutic approaches to metabolic syndrome. One is lifestyle modification to reduce insulin resistance, which is the cause of metabolic syndrome, and the other is pharmacotherapy for each component of metabolic syndrome.

Obesity is a disease associated with increased socioeconomic burden due to increased risk of obesity-related comorbidities. Since obesity is multifactorial, treatments for obesity include comprehensive lifestyle interventions such as nutrition therapy, physical activity, behavior therapy, and pharmacotherapy. The proper surgical management of obesity requires a multidisciplinary treatment team. This new guideline helps primary care physicians make safer and more effective decisions by providing evidence-based recommendations with clear evidence levels and high-quality evidence-based information. More efforts are needed to improve the quality of obesity treatment and management in Korea.

Ga Eun Nam has worked as an Associate Editor of the journal since 2020. However, she was not involved in the peer reviewer selection, evaluation, or decision process of this article. Otherwise, no other potential conflicts of interest relevant to this article were reported.

This work was supported by the Korean Society for the Study of Obesity.

Study concept and design: BYK and CHK; acquisition of data: SMK, JHK (Jee-Hyun Kang), SYK, KKK, and BK; analysis and interpretation of data: SJK, YHK, JHK (Jae Hyun Kim), HL, EJJ, SC, KBK, YAS and YHH; drafting of the manuscript: BYK and CHK; critical revision of the manuscript: BYK, EMK, SMK, JHK (Jee-Hyun Kang), SYK, KKK, BK, SJK, YHK, JHK (Jung-Hwan Kim), JHK (Jae Hyun Kim), GEN, JYP, JWS, HJS, TJO, HL, EJJ, SC, YHH, YAS and CHK; statistical analysis: SJK, YHK, and JHK (Jung-Hwan Kim); obtained funding: BYK and CHK; administrative, technical, or material support: BYK and CHK; and study supervision: CHK.