When we think of obesity, we often picture obvious signs: a high number on the scales, clothes feeling tight, or someone recognising that they are significantly “over weight”. Yet in reality, many people may have excess body fat or be on the path to health risk without fully appreciating it — and without realising they meet clinical definitions of obesity.
Here’s a closer look at how this can happen, why it matters, and what you can do about it.
What defines obesity?
The most commonly used measure is the Body Mass Index (BMI) — your weight in kilograms divided by your height in metres squared. According to standard UK and international guidance:
- A BMI of 18.5-24.9 kg/m² is considered “normal”.
- A BMI of 25-29.9 kg/m² is considered overweight.
- A BMI of 30 kg/m² or more is considered class I obesity (with higher classes above 35, 40).
However — and this is key — BMI is a screening tool not a definitive diagnosis. It does not capture how fat is distributed in the body, nor how much of your mass is muscle vs fat.
Why you might be obese without realising it
- Normalisation of higher body weights: As heavier weights become more common in the population, what counts as “normal” may shift in people’s minds. Studies show that many people whose objectively-measured BMI falls in the overweight or even obese range do not perceive themselves as overweight.
- Muscle vs fat confusion: Because BMI doesn’t distinguish muscle from fat, someone with high muscle mass (e.g., athlete) may have a high BMI and not much fat. Conversely, someone may have a “moderate” BMI but high visceral fat and be at greater risk without realising.
- Fat distribution matters: Fat stored around the abdomen — so-called visceral fat — is more strongly linked with health risk than fat stored in other areas. So someone with a “normal” looking body or moderate BMI may still have elevated risk if their waist/hip/height ratios are unfavourable.
- Self-perception and social context: Because many people around us may be heavier than in previous generations, individuals may underestimate their own weight status. One study found that a sizeable portion of adults underestimate their weight status (especially men) with overweight or obesity.
Why it matters
Excess body fat and obesity are strongly associated with increased risk of major health conditions including type 2 diabetes, cardiovascular disease, some cancers, joint diseases and reduced life expectancy.
If you do not recognise that you have obesity (or excess adiposity) you may:
- Delay seeking help (lifestyle change, medical assessment, weight-loss treatment)
- Stay in a ‘grey zone’ where risk is increasing but action is not taken
- Miss the opportunity to engage earlier when less invasive or intensive interventions may suffice
Practical signs that you might be obese or at high risk, even if you don’t “feel” it
Here are some red flags beyond simply “I feel heavy”:
- Your BMI is 30 kg/m² or above — this triggers the definition of obesity.
- Your waist circumference is elevated: for men >102 cm and women >88 cm are commonly used risk thresholds.
- You carry much of your weight around the abdomen (apple shape) rather than hips/thighs (pear shape).
- You have high-risk markers such as elevated blood pressure, cholesterol, fasting glucose, or you have joint pains (knees, hips) or sleep apnoea.
- You don’t recognise yourself as “obese” but your clothes, energy levels, health markers or mobility are gradually deteriorating.
- You compare to your immediate peers and think you look “about the same” — yet if the reference group is heavier, you may under-estimate your own risk.
What to do next (and when to seek specialist help)
If you suspect you may have excess weight/adiposity, the following steps are wise:
- Calculate your BMI (weight ÷ height²) as a starting point.
- Measure your waist circumference (at the narrowest point after exhaling) and check against risk thresholds.
- Review your overall health: Do you have high blood pressure, high blood sugar, sleep issues, joint pain, low energy?
- Make an honest self-assessment: even if you ‘look similar’ to friends/colleagues, their weight may not be a healthy benchmark.
- Seek advice from a specialist — for example the team at Harley Street Obesity Clinic — if:
- Your BMI is ≥ 30 or ≥ 35 with other risk factors;
- You have attempted lifestyle changes (diet/exercise) without sufficient change;
- You have obesity-related conditions (diabetes, joint problems, sleep apnoea).
- Remember: obesity is a medical condition not simply a lifestyle issue. Professional assessment may include body composition, metabolic screening, discussion of surgical or non-surgical weight-loss options.
It’s entirely possible to look ok and feel pretty normal — yet still carry excess fat, be on a trajectory of increasing risk, and meet the clinical definition of obesity without that realisation. Recognising the fact is the first step. Once recognised, you gain access to interventions that are far more effective the sooner they are started.
At the Harley Street Obesity Clinic we believe in compassionate, evidence-based assessment, and helping patients understand their risks, their options and their way forward — not just in terms of weight, but of health, mobility and quality of life. If you’ve read this and thought “That’s me but I didn’t realise”, please do book a consultation and let’s take the next step together.