Weight Management

Introduction

Around two-thirds of adults in England are living with overweight or obesity, making weight management one of the most frequent, and most sensitive, conversations in general practice.¹ Obesity is a chronic, relapsing condition shaped by genetic, physiological, environmental and psychological factors, not simply a matter of willpower - guidance and exam questions increasingly reflect this framing.

It matters because excess adiposity is causally linked to type 2 diabetes, hypertension, ischaemic heart disease, obstructive sleep apnoea, osteoarthritis, several cancers, non-alcoholic fatty liver disease and reduced fertility, and because even modest sustained weight loss produces disproportionate metabolic benefit.

Assessment

Body mass index (BMI) = weight (kg) / height (m)². It classifies risk at a population level but is an imperfect individual measure - it does not distinguish fat from muscle mass and does not describe fat distribution.

Waist circumference adds independent information about visceral (central) fat, which carries more metabolic risk than peripheral fat, and is particularly useful when BMI is 25-34.9.

A full assessment also covers eating pattern, physical activity, sleep, alcohol intake, medication that promotes weight gain (for example some antipsychotics, insulin, sulfonylureas, some antidepressants and corticosteroids), mental health, and screening for obesity-related complications such as blood pressure, HbA1c, lipid profile and liver function.

The tiered weight management pathway

NHS weight management services are organised into four tiers, of which the first two are largely delivered in or accessed through primary care.³

Lifestyle and behavioural intervention

A structured behavioural programme is first-line for almost everyone, and should be tried, or run in parallel, before or alongside drug treatment - not simply used as a gatekeeper before 'real' treatment.

• Dietary change: an individualised, sustainable calorie deficit rather than a restrictive short-term diet - very low calorie diets can produce rapid loss but are harder to sustain and are used only in specific, time-limited, supervised circumstances
• Physical activity: at least 150 minutes of moderate-intensity activity a week, built up gradually - more important for weight maintenance and metabolic health than for weight loss itself, where diet has the larger initial effect
• Behaviour change techniques: self-monitoring (food diaries, weighing), goal-setting, stimulus control, and relapse-prevention planning
• Sleep and stress: poor sleep and chronic stress both promote weight gain via appetite-regulating hormones (ghrelin, leptin, cortisol) and are worth addressing explicitly

Pharmacotherapy

Drug treatment is considered when lifestyle measures alone have not achieved or maintained sufficient loss, generally alongside continued lifestyle support rather than instead of it.

Common side effects of GLP-1 agonists are gastrointestinal - nausea, vomiting, diarrhoea, constipation - usually improving with dose titration. Rare but important risks include pancreatitis and, for some agents, gallstone disease; they should be used cautiously or avoided in a history of pancreatitis, and are not recommended in pregnancy.

Bariatric surgery

Bariatric (metabolic) surgery is the most effective and durable intervention for severe obesity, producing substantially greater and more sustained weight loss than any non-surgical option, along with marked improvement or remission of type 2 diabetes in many patients.

• BMI ≥40, or BMI ≥35 with a significant obesity-related comorbidity (for example type 2 diabetes, hypertension, obstructive sleep apnoea)
• All appropriate non-surgical measures have been tried without adequate sustained result
• The person is fit for anaesthesia and surgery, and able to commit to long-term follow-up
• For people of South Asian, Chinese and some other ethnic groups with a lower diabetes risk threshold, surgery may be considered at a BMI 2.5 kg/m² lower than the standard cut-off

Common procedures are sleeve gastrectomy (restrictive, removing most of the stomach) and Roux-en-Y gastric bypass (restrictive and mildly malabsorptive). Both require lifelong nutritional monitoring and supplementation - particularly iron, calcium, vitamin D and vitamin B12 after bypass, where the malabsorptive component is greater.

Secondary causes and contributing factors

The great majority of obesity is multifactorial rather than attributable to a single endocrine cause, but a small number of secondary causes and contributing factors are worth actively considering, particularly where weight gain has been rapid, disproportionate, or accompanied by other suggestive features.

Weight stigma and communication

Weight-related stigma from healthcare professionals is well documented and has real clinical consequences: patients who feel judged are more likely to avoid or delay seeking care, including for unrelated symptoms, and attributing every presentation to weight without adequate assessment is a recognised cause of diagnostic delay.

• Ask permission before discussing weight ("Would it be alright if we talked about your weight today?")
• Use neutral, person-first language ("a person with obesity" rather than defining someone by their weight)
• Avoid assuming a symptom is weight-related without appropriate assessment
• Recognise obesity as a chronic condition shaped by biology and environment, not a failure of willpower

Physiology of weight regulation

Body weight is defended by a set of homeostatic mechanisms that evolved to protect against starvation, which is why sustained weight loss is physiologically harder than the simple 'calories in, calories out' framing suggests - and why relapse should be understood as expected biology rather than as a failure of character.

• Leptin, secreted by adipose tissue in proportion to fat mass, signals energy sufficiency to the hypothalamus. Levels fall with weight loss, driving increased appetite; most people with obesity are leptin-resistant rather than leptin-deficient, which is why leptin itself is not a useful treatment
• Ghrelin, secreted by the stomach, stimulates appetite and rises with weight loss and before meals
• GLP-1 and PYY, secreted by the distal small bowel after eating, promote satiety and slow gastric emptying - the pathway exploited by GLP-1 receptor agonist drugs and enhanced anatomically by gastric bypass
• Adaptive thermogenesis: resting energy expenditure falls after weight loss by more than would be predicted from the reduced body mass alone, so a person who has lost weight requires fewer calories to maintain that weight than someone of the same weight who never lost it

Complications of obesity

• Metabolic: type 2 diabetes, dyslipidaemia, non-alcoholic fatty liver disease
• Cardiovascular: hypertension, ischaemic heart disease, heart failure, venous thromboembolism
• Respiratory: obstructive sleep apnoea, obesity hypoventilation syndrome, asthma exacerbation
• Musculoskeletal: osteoarthritis, particularly weight-bearing joints, and chronic back pain
• Reproductive: polycystic ovary syndrome, subfertility, higher-risk pregnancy
• Malignancy: endometrial, breast (postmenopausal), colorectal, oesophageal and renal cancer
• Psychological: depression, anxiety, low self-esteem, disordered eating, and the effects of stigma itself

Red flags

Prognosis

Weight regain after lifestyle intervention alone is common because the body defends against weight loss through compensatory changes in appetite hormones and energy expenditure - this is physiological, not a sign of a patient's lack of effort, and is part of why obesity is now understood as a chronic relapsing condition requiring ongoing management rather than a single course of treatment.

Combining structured lifestyle support with pharmacotherapy or surgery where indicated, and maintaining long-term follow-up, produces the most durable outcomes and the greatest reduction in obesity-related morbidity and mortality.

The practical consequence for how obesity is managed is that treatment should not be conceived as a time-limited course after which the patient is discharged 'cured'. GLP-1 receptor agonists illustrate this directly: weight is regained substantially after stopping the drug, in the same way blood pressure rises again after stopping an antihypertensive, which reflects the chronic nature of the underlying condition rather than a failure of either the drug or the patient. Framing this openly at the outset avoids the patient interpreting later weight regain as a personal failure.