Obesity | Overweight | Excessive Weight - Get more information and expert advice on treating severe obesity

Obesity (also known as adiposity) describes a pathological increase in body fat.

The World Health Organization (WHO) defines obesity using the Body Mass Index (BMI), which indicates the ratio of body weight to height.

BMI = Body weight (kg) / (Height in meters)²

The WHO classifies a BMI of 30 or higher as obesity.

WHO BMI Classification:

• Normal weight: 18.5–24.9 kg/m²
• Overweight: 25–29.9 kg/m²
• Class 1 obesity: 30–34.9 kg/m²
• Class 2 obesity: 35–39.9 kg/m²
• Class 3 obesity (severe obesity): ≥ 40 kg/m²

In addition to BMI, body composition (proportion of muscle mass or fat distribution) is also important. 

The BMI calculator serves as a guide but is not a substitute for a medical evaluation. A high BMI in athletic individuals may be due to muscle mass and does not automatically mean they are overweight. 

Obesity develops as a result of a positive energy balance. If the body receives more energy (in the form of calories) than it expends, the excess energy is stored as fat.

Lifestyle and Diet

A key risk factor is an unhealthy lifestyle characterized by a lack of physical activity, a high-calorie diet, and high sugar and fat intake. Frequent snacking, sugary drinks, and fast food also contribute to the development of obesity.

Genetic and Hormonal Factors

Basal metabolic rate (i.e., energy expenditure at rest) is partly genetically determined. Some people are therefore more prone to weight gain.

Endocrine disorders such as hypothyroidism or Cushing’s syndrome can also contribute to the development of obesity. 

Psychological causes of obesity and eating disorders

Emotional stressors such as stress, anxiety, or depression often lead to binge eating. Eating disorders such as bulimia, binge eating disorder, or night eating syndrome are more common in people with obesity.

Medications and Other Triggers

Certain medications (e.g., antidepressants, antipsychotics, or glucocorticoids) can increase the risk of being overweight or obese.

Inactivity, pregnancy, or quitting smoking can also play a role.

Conclusion:

Obesity is usually multifactorial and the result of genetic, psychological, hormonal, and behavioral influences.

People with obesity have a significantly higher risk of developing numerous complications:

• Type 2 diabetes
• High blood pressure and cardiovascular diseases
• Stroke and coronary heart disease
• Lipid metabolism disorders
• Osteoarthritis and joint problems
• Sleep apnea
• Depression
• Certain types of cancer

As the degree of obesity increases, the likelihood of developing related conditions rises significantly.

Studies show that reducing BMI by just 5–10% lowers the risk of diabetes mellitus and other diseases.

Obesity increases the risk of premature death, especially when left uncontrolled and untreated.

Therefore, the earlier treatment begins, the better the prognosis.

The treatment of obesity occurs in several stages and should always be tailored to the individual. The goal is to reduce body weight over the long term and prevent comorbidities.

Conservative Therapy

Conservative treatment is based on three pillars: diet, exercise, and behavior.

Nutritional Therapy

Patients with obesity should consume 500–1,000 kcal less per day than they have been. Foods that are high in fiber, low in fat, low in sugar, and nutrient-dense are recommended.

In the long term, a balanced, varied diet in accordance with the guidelines of the German Nutrition Society (DGE) has proven effective.

Extreme diets or crash diets are not suitable. They carry significant medical risks and usually lead to the yo-yo effect.

Exercise Therapy

Regular physical activity increases energy expenditure, improves fitness, and stabilizes weight. The recommendation is 30–50 minutes of exercise 3–5 days per week (e.g., walking, cycling, swimming).

Behavioral Therapy

The goal is to change eating and exercise habits in the long term. Keeping a food diary, self-monitoring, stress management, and relapse prevention are also helpful in this regard.

This form of therapy primarily supports long-term stability after weight loss.

Medication

If sufficient weight loss is not achieved despite consistent basic therapy, various medication-based treatment options can be used. Your doctor will explain these to you.

One example is the active ingredient orlistat, which inhibits fat digestion and is prescribed for patients with a BMI greater than 28. 

However, medications are not a substitute for continuing conservative measures.

Since 2023, so-called “weight-loss injections,” such as semaglutide, have also been approved. They can be prescribed by a doctor for a BMI >30 or for a BMI >28 accompanied by comorbidities. 

Surgical Treatment—Bariatric Surgery 

Surgery may be considered for patients with a BMI of 40 or higher, or for those with a BMI of 35 or higher who have severe comorbidities (e.g., type 2 diabetes mellitus).

Surgical Methods

• Sleeve Gastrectomy
• Gastric bypass
• Biliopancreatic Diversion (BPD)

These procedures reduce the size of the stomach or limit nutrient absorption, resulting in weight loss (restriction and malabsorption).

Risks and Follow-Up Care

Complications are relatively rare. For example, approximately 1–2% of cases experience wound healing complications or thrombosis.

An important component of postoperative care is lifelong follow-up and monitoring of nutrient intake, weight stabilization, and relapse prevention.

Goal of surgical treatment:

long-term weight stability, reduction of comorbidities, and improvement in quality of life.

Contraindications for surgery as a treatment for obesity include:

• drug and alcohol dependence
• substance use disorders and immunodeficiency disorders
• Bulimia nervosa
• Psychoses and personality disorders

Complications following bariatric surgery occur in 1–2% of obese patients. These primarily include

• wound-healing disorders,
• thrombosis,
• pulmonary embolisms.

Ideally, obesity prevention begins as early as childhood and adolescence. 

According to the Working Group on Obesity in Children and Adolescents, promoting physical activity, a healthy diet, and education are the most effective measures.

Prevention also plays a crucial role in adulthood:
a healthy lifestyle, regular physical activity, and weight management can prevent obesity in adulthood.

The German Society for Obesity, as well as international organizations such as the WHO, regularly publish guidelines (e.g., Technical Report Series 894) on the prevention and treatment of obesity.

Patients with obesity benefit from interdisciplinary care provided by physicians, nutritionists, exercise therapists, and psychologists.
Specialized obesity centers offer combined programs and surgical procedures in accordance with the guidelines of the German Society for Obesity.

Anyone wishing to learn about individual treatment options can use a BMI calculator for guidance and seek medical advice.
Long-term success is achieved when treatment is holistic and aims for sustainable lifestyle changes.