Describe obesity and the metabolic syndrome.

Obesity and the Metabolic Syndrome

• Measurement — body mass index = weight in kg / (height in metres)²
• The ASIAN cut-offs are lower than the international ones, and using the wrong set is a common error — overweight at 23 to 24.9 and obesity at 25 kg/m² or above for Asians, against 25 and 30 internationally
• The reason is the "thin-fat" phenotype — South Asians carry more body fat and more visceral fat, and show greater insulin resistance, at any given BMI, so metabolic risk begins at a lower weight
• BMI has real limitations that should be stated — it does not distinguish fat from muscle, nor indicate fat distribution, and therefore misclassifies muscular individuals and misses the "normal-weight obese"
• Waist circumference measures central (visceral) obesity, which is the metabolically dangerous compartment; the Asian cut-offs are 90 cm in men and 80 cm in women
• Waist-to-hip ratio and waist-to-height ratio are alternatives, the latter with the useful rule that waist should be less than half of height
• The causes — fundamentally a chronic positive energy balance, but that formulation is unhelpful on its own, because it locates the problem entirely in individual willpower
• The obesogenic environment is the more useful concept — cheap, energy-dense, aggressively marketed processed food; sugar-sweetened beverages; larger portions; mechanised transport and work; urban design hostile to walking; screen time; and reduced sleep
• Contributing factors — genetic predisposition; endocrine causes such as hypothyroidism and Cushing syndrome, which are rare; drugs including steroids, some antipsychotics and insulin; and fetal and infant programming, with low birth weight followed by rapid catch-up growth carrying particular risk
• The consequences — type 2 diabetes, for which obesity is the dominant risk factor; hypertension and cardiovascular disease; dyslipidaemia; several cancers; obstructive sleep apnoea; non-alcoholic fatty liver disease; osteoarthritis; gallstones; polycystic ovary syndrome and infertility; and psychological effects including depression and the consequences of stigma
• The metabolic syndrome is a clustering of central obesity, raised triglycerides, low HDL, raised blood pressure and raised fasting glucose, with three of the five required for the diagnosis
• Its value is that it identifies a person at high total cardiovascular and diabetes risk in whom NO single factor may be alarming
• Prevention and management — dietary change, reducing refined carbohydrate, sugar and fat and increasing fibre, fruit and vegetables; physical activity of at least 150 minutes of moderate activity weekly, with muscle strengthening twice weekly; behavioural support; pharmacotherapy in selected cases; and bariatric surgery for severe obesity
• A realistic target is a 5 to 10% weight loss, which produces substantial metabolic benefit and is far more achievable than a return to ideal weight; maintenance is harder than loss and needs continuing support
• Population measures — taxation of sugar-sweetened beverages; front-of-pack labelling; restricting marketing to children; school food and activity policy; trans fat elimination; and urban design promoting walking and cycling
• Childhood obesity is rising fastest in Indian cities and matters particularly because it tracks into adulthood
• Use the Asian cut-offs, not the international ones, or a great many at-risk Indians are classified as normal
• Waist ninety and eighty centimetres are the Asian thresholds for men and women respectively
• Aim for five to ten per cent weight loss, which delivers most of the metabolic benefit and is achievable
• Maintenance is harder than losing, and needs continuing support rather than a discharge at target
• BMI cannot distinguish fat from muscle, nor show its distribution, which is why waist is measured too
• Visceral fat is the dangerous compartment, which is what waist circumference is actually measuring
• Three of five features define metabolic syndrome, identifying high total risk where no single factor alarms
• Energy balance alone is an unhelpful formulation, since it locates the whole problem in individual willpower
• The obesogenic environment is the useful concept, covering cheap energy-dense food, marketing and mechanised life
• Endocrine causes are rare, and should not be the first line of investigation in an obese patient
• Low birth weight with rapid catch-up carries particular later risk, which is specifically relevant in India
• Childhood obesity tracks into adult life, which is why school policy is a long-term NCD measure
• Waist should be under half of height, which is a simple rule usable without any chart