Weight Loss
Overview
Weight loss is a phenomenon in which the total mass of the body decreases, primarily due to reductions in body fat and muscle mass. Intentional weight loss is achieved through dietary therapy, exercise, medication, or surgery for the treatment of obesity or health promotion, while unintentional weight loss may signal underlying diseases (such as cancer, diabetes, hyperthyroidism, or gastrointestinal disorders) and requires attention. Weight loss occurs when energy intake is less than energy expenditure, and rapid short-term loss can lead to nutritional imbalances or metabolic abnormalities.
Main Content
Physiological Mechanisms of Weight Loss
Weight loss occurs through three main pathways: (1) Decreased energy intake – due to poor appetite, oral issues, depression, etc., leading to reduced calorie intake; (2) Increased energy expenditure – due to excess thyroid hormones, fever, increased physical activity, etc., raising basal metabolic rate; (3) Nutrient malabsorption – due to conditions such as Crohn's disease, celiac disease, or chronic pancreatitis, where ingested nutrients are not properly absorbed. A loss of 1 kg of body weight requires an energy deficit of approximately 7,700 kcal, which corresponds to the energy content of 1 kg of fat.
Methods of Intentional Weight Loss
Dietary Therapy: Low-calorie diets (1,200–1,500 kcal per day), low-carbohydrate diets (ketogenic diet), and intermittent fasting (16:8 method, 5:2 method) are widely used. Maintaining adequate protein intake to prevent muscle loss is important.
Exercise: Aerobic exercise (walking, running, cycling) is effective for calorie burning, while resistance training (weight training) increases basal metabolic rate and preserves muscle mass. The American College of Sports Medicine (ACSM) recommends 150–250 minutes of moderate-intensity exercise per week.
Pharmacotherapy: Appetite suppressants (phentermine, bupropion-naltrexone), fat absorption inhibitors (orlistat), and GLP-1 receptor agonists (semaglutide, liraglutide) are used. Recently, semaglutide (Wegovy, Ozempic) has gained attention for its potent weight loss effects.
Surgical Therapy: Sleeve gastrectomy, gastric bypass, and adjustable gastric banding are performed, typically for patients with a body mass index (BMI) of 35 or higher. Average weight loss after surgery reaches 25–30%.
Causes of Unintentional Weight Loss
Unintentional weight loss is defined as a loss of more than 5% of body weight over 6–12 months. Major causes include malignant tumors (lung cancer, stomach cancer, pancreatic cancer, etc.), endocrine disorders (hyperthyroidism, diabetes), gastrointestinal diseases (inflammatory bowel disease, malabsorption syndromes), chronic infections (tuberculosis, HIV), anorexia nervosa, depression, and medication side effects (chemotherapy, excessive thyroid hormone intake). In particular, unintentional weight loss in the elderly can lead to sarcopenia and weakened immunity, making early diagnosis crucial.
Health Effects of Weight Loss
Appropriate weight loss helps improve obesity-related conditions (type 2 diabetes, hypertension, dyslipidemia, sleep apnea). Even a 5–10% reduction in body weight significantly improves blood glucose, blood pressure, and cholesterol levels. Conversely, rapid or excessive weight loss can cause nutritional deficiencies (iron, calcium, vitamin D deficiency), gallstones, hair loss, menstrual irregularities, decreased bone density, impaired immune function, and weight regain (yo-yo effect). Excessive loss of muscle mass lowers basal metabolic rate, making long-term weight management difficult.
Monitoring and Evaluation of Weight Loss
To assess the progress of weight loss, methods such as weight measurement (once a week under the same conditions), body composition analysis (body fat percentage, muscle mass), waist circumference measurement, and blood tests (thyroid hormones, blood glucose, inflammatory markers) are used. For intentional weight loss, a rate of 0.5–1 kg per week is considered safe and sustainable. If unintentional weight loss is suspected, further evaluation with endoscopy, imaging (CT, MRI), or biopsy may be necessary to identify underlying diseases.
Recent Trends
As of 2024–2025, GLP-1 receptor agonists (semaglutide, tirzepatide) have established themselves as innovative treatments in the field of weight loss. These drugs induce an average weight loss of 15–20% by suppressing appetite and increasing satiety, and have also demonstrated cardiovascular risk reduction benefits. Additionally, advances in digital health technology have popularized AI-based diet tracking apps, wearable devices for activity monitoring, and telemedicine consultations. Personalized dietary strategies using nutritional genomics (nutrigenomics) are gaining attention, and research on weight management through gut microbiome modulation is actively ongoing. Along with improved accessibility to obesity medications, there is a notable shift in societal perception recognizing obesity as a chronic disease. However, long-term safety concerns (gastrointestinal side effects, risk of thyroid tumors) and high costs remain challenges.
Related Topics
- [[Obesity]]
- [[Dieting]]
- [[Nutrition]]
- [[Metabolic syndrome]]
- [[GLP-1 receptor agonist]]
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