Obesity

🔍 When to Suspect

Formally identified by calculating Body Mass Index (BMI); assess any adult with a BMI ≥ 30 kg/m² (obese) or BMI 25-29.9 kg/m² (overweight), and measure waist circumference to assess central adiposity

From the full topic in The Ocean Library: Obesity

🧭 When to suspect

Obesity is a chronic, relapsing condition of excess adiposity.

• It drives type 2 diabetes mellitus (T2DM), cardiovascular disease (CVD), several cancers, obstructive sleep apnoea (OSA), fatty liver and mechanical joint disease.

• The National Institute for Health and Care Excellence (NICE) guideline NG246 (2025) reframes it as a long-term condition needing ongoing, non-stigmatising support – not a one-off failure of willpower.

• NG246 replaces the older CG189.

Identify and stratify using two measures together: body mass index (BMI), and – in any adult with a BMI under 35 – waist-to-height ratio (WtHR), which captures the central adiposity that BMI misses.

Interpret BMI with caution:

• Thresholds are lower in several ethnic groups

• High muscle mass inflates it

• It should be read cautiously in people aged 65 and over

The two clinical tasks are to stratify risk and to exclude a secondary or sinister cause before attributing weight to lifestyle alone.

Classification	BMI (kg/m²)	Higher-risk ethnic groups*
Healthy weight	18.5–24.9	18.5–22.9
Overweight	25.0–29.9	23.0–27.4
Obesity – class 1	30.0–34.9	≥ 27.5
Obesity – class 2	35.0–39.9	32.5–37.4
Obesity – class 3 (severe)	≥ 40.0	≥ 37.5

*Apply lower thresholds (a ~2.5 kg/m² reduction), for both classification and drug eligibility, for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background, in whom cardiometabolic risk rises at a lower BMI.

Central adiposity (BMI < 35)	Waist-to-height ratio	Health risk
Healthy	0.4–0.49	No increased risk
Increased	0.5–0.59	Increased risk
High	≥ 0.6	Further increased risk

WtHR uses the same cut-offs for both sexes and all ethnicities and is summarised for patients as: “keep your waist to less than half your height” (ratio under 0.5).

Be especially alert in those with:

• A family history of obesity or T2DM

• Weight-promoting medication (antipsychotics, some antidepressants, corticosteroids, insulin/sulfonylureas)

• Polycystic ovary syndrome (PCOS)

• Hypothyroidism

• Poor sleep

• Low mood

• Social deprivation

Source: NICE NG246

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