Weight loss: causes, methods, risks and practical guidance

How weight changes occur

At a basic level, weight change results from an imbalance between energy intake (food and drink) and energy expenditure (basal metabolism, physical activity, digestion). Hormones, genetics, age, sleep, stress and some medications also influence appetite and how the body stores or burns energy. Body composition—how much of the weight is fat versus muscle or water—affects both health outcomes and how weight responds to interventions.

Common approaches

Most non-surgical strategies combine changes in diet, increased physical activity, and behavioural support. Examples include:

• Exercise: regular aerobic and resistance activity such as running or swimming can increase calorie use and preserve muscle.
• Nutrition: adopting a diet with smaller portion sizes, fewer energy-dense processed foods, and more whole foods such as vegetables, fruits and lean meat often helps lower calorie intake while maintaining nutrients.
• Behavioural strategies: goal setting, self-monitoring, problem solving and social support improve adherence and long-term success.

Medical and surgical options

For people with significant obesity or weight-related health conditions, clinicians may recommend medical therapies or bariatric surgery. Prescription medications can alter appetite, absorption or metabolism and are used under medical supervision. Surgical procedures change the digestive system to reduce intake or absorption and can produce substantial and sustained weight loss for selected patients. All medical interventions require assessment of benefits, risks and follow-up care.

Risks, limitations and important distinctions

Rapid or extreme weight loss can cause nutrient deficiencies, loss of muscle, gallstones or other complications. Weight on the scale can fluctuate day to day because of fluid balance, so single measurements are less informative than trends and measures of body composition. ‘‘Healthy’’ weight is individualized: a modest, sustained loss that improves blood pressure, glucose control or mobility can be more important than achieving a specific number.

When to seek professional advice: consult a healthcare provider before beginning major diets or exercise programs, especially if there are existing medical conditions, pregnancy, or use of medications. Sustainable change tends to emphasize gradual modifications, balanced nutrition, regular activity and realistic goals rather than quick fixes.