Obesity: Why the Definition Is Changing and What It Means for Your Health in Ireland
Introduction: Why the Definition of Obesity Matters
For years, doctors and public health bodies in Ireland and worldwide have relied on Body Mass Index (BMI) to define obesity. While BMI is quick and widely used, it has important limitations. Two people with the same BMI can have very different health risks. To start, you can check your BMI here.
Now, global experts are shifting towards a more accurate way of defining obesity, one that looks beyond numbers on a scale. If you’re concerned about weight, waist size, or conditions like diabetes or heart disease, understanding this change is essential.
What Is Obesity?
The World Health Organisation (WHO) defines obesity as abnormal or excessive fat accumulation that increases health risk. Traditionally, BMI has been the go-to tool:
| Classification | BMI (kg/m²) |
|---|---|
| Underweight | <18.5 |
| Normal weight | 18.5–24.9 |
| Overweight | 25–29.9 |
| Obese | ≥30 |
BMI is easy to calculate, but it does not always tell the full story. A rugby player with strong muscle mass may fall into the “obese” range, while someone with a “normal” BMI but excess belly fat may face serious risks like heart disease.
What’s Changing in the Definition of Obesity?
International research groups, including The Lancet and public health organisations like the CDC, are calling for a shift. Instead of relying only on BMI, the new definition asks two key questions:
- Do you have excess body fat?
Doctors may use BMI, waist size, waist-to-hip ratio, or direct fat measurements. - Is that fat harming your health?
– Preclinical obesity: extra fat but no current health problems.
– Clinical obesity: extra fat plus health issues such as high blood sugar, high blood pressure, or fatty liver.
This means obesity is no longer only about a number. It is about whether fat is already affecting your organs and long-term health.
Why Your Waist Size Is So Important
Where fat is stored often matters more than how much you weigh. Belly fat, also known as visceral fat, is strongly linked to health problems like type 2 diabetes and cardiovascular disease.
The HSE and Irish Heart Foundation recommend keeping waist size below these cut-offs:
- Men: under 94 cm (37 inches)
- Women: under 80 cm (32 inches)
A higher waist circumference significantly raises your risk of heart disease, regardless of your BMI.
What This Means for You
- You are more than your BMI. A single number does not define your health.
- Early checks are valuable. Doctors may act sooner if excess fat is present, even before illness develops.
- Care is personalised. Two people with the same BMI may receive different advice depending on fat distribution and test results.
- Less stigma, more support. Obesity is being recognised as a chronic condition, not simply about looks or “willpower.”
What You Can Do Now
- Check both BMI and waist size. These give a clearer picture together.
- Ask your doctor for tests. Blood sugar, cholesterol, and blood pressure are key health indicators.
- Prioritise health habits. A balanced diet, regular movement, quality sleep, and moderating alcohol make a big difference.
- Act early. Preclinical obesity is a warning sign—taking steps now reduces future risks.
FAQs About Obesity
What is preclinical obesity?
Preclinical obesity means you have excess body fat but no health damage yet. It is an early warning sign.
Is BMI still useful?
Yes, but it should be combined with waist size and health checks for a clearer picture.
Can someone have obesity without being overweight?
Yes. Even at a “normal” BMI, excess belly fat can increase risk.
What is the safest waist size in Ireland?
The HSE and Irish Heart Foundation recommend under 94 cm for men and under 80 cm for women.
The Bottom Line
Obesity is not only about weight or appearance. It is about how body fat affects your health. The updated definition distinguishes between:
- Preclinical obesity – excess fat with no current organ damage
- Clinical obesity – excess fat already causing harm
By moving beyond BMI, healthcare in Ireland can become more accurate, personalised, and supportive.
Book a Consultation Today
Concerned about your weight, waist size, or health risks? You don’t need a referral or a waiting list. Book a consultation today with a Webdoctor GP or Irish-registered dietitian and get expert, personalised advice to protect your long-term health.