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Waist Size Tells You More Than BMI: Visceral Fat and Your Real Risk

NICE advises keeping your waist under half your height. Dr. Sayantan Banerjee explains waist-to-height ratio, visceral fat, US and UK cut-offs, and how to measure at home.

OBESITY REMISSION

Dr. Sayantan Banerjee

10/31/20267 min read

BMI is a quick sum: your weight in kilograms divided by your height in metres squared. It was devised in the 19th century by the Belgian mathematician Adolphe Quetelet to describe populations, not individuals. It is still useful for comparing large groups and for a rough first check. For a single person, though, it misses a lot.

A muscular rugby player and a sedentary office worker can have exactly the same BMI and very different health. Two people with a BMI of 27 can have very different risks of diabetes and heart disease. The biggest thing BMI can't tell you is where your fat is stored. For metabolic health, that matters more than the total.

This article explains the difference between types of body fat, why your waist is such a useful measure, the US and UK cut-offs, and how to measure yourself properly at home.

Not all fat is the same

Subcutaneous fat sits under the skin, mainly on the hips, thighs, buttocks and arms. It is the fat you can pinch. In moderate amounts it is relatively harmless, and fat on the hips and thighs may even be protective in some ways.

Visceral fat sits deep inside the abdomen, wrapped around the liver, intestines, stomach and pancreas. It behaves very differently. It is more metabolically active. It releases fatty acids and inflammatory signals directly into the portal vein, which carries blood straight to the liver.

Ectopic fat is fat stored inside organs where it shouldn't be, such as the liver, pancreas, heart and muscle. It often travels with visceral fat.

Visceral and ectopic fat are closely linked to insulin resistance, type 2 diabetes, high triglycerides, low HDL cholesterol, high blood pressure, fatty liver disease (now called MASLD), and heart disease. Two people with the same weight can carry very different amounts of it.

You can't see visceral fat directly without a scan. But your waist measurement is a surprisingly good stand-in.

The simplest test: half your height

In 2022, NICE in the UK updated its obesity guidance with a simple rule: keep your waist to less than half your height.

To check it, divide your waist measurement by your height, using the same units, both in centimetres or both in inches.

0.4 to 0.49 — What it means (NICE): No increased health risk
0.5 to 0.59 — What it means (NICE): Increased health risk
0.6 or more — What it means (NICE): High health risk

Example: you are 5 ft 7 in, which is 67 inches or about 170 cm. Half your height is 33.5 inches (85 cm). If your waist is 37 inches (94 cm), your ratio is about 0.55. That falls in the increased-risk band, even if your BMI looks normal.

The same rule works for men and women and across ethnic groups, which is a large part of its appeal. It also works for most adults with a BMI under 35. NICE suggests using it alongside BMI, not instead of it.

US waist cut-offs

In the US, long-standing NIH guidance uses waist circumference on its own. A waist above 40 inches (102 cm) for men or 35 inches (88 cm) for women signals a higher risk of type 2 diabetes, high blood pressure and heart disease, especially in people with a BMI between 25 and 35. Lower cut-offs are often used for people of Asian heritage, such as 35 inches (90 cm) for men and 31 inches (80 cm) for women.

The World Health Organization also uses the waist-to-hip ratio, with higher risk above 0.90 for men and 0.85 for women. This is less commonly used in everyday practice, because it needs two measurements.

Why ethnicity matters

People of South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean heritage tend to carry more visceral fat at the same BMI, and they develop type 2 diabetes at lower weights and younger ages.

For that reason NICE uses lower BMI thresholds for these groups: 23 for overweight and 27.5 for obesity, instead of 25 and 30. The waist-to-height rule helps here too, because it doesn't need a separate cut-off.

A change in how obesity is diagnosed

In January 2025, a global commission published in The Lancet Diabetes & Endocrinology argued that BMI alone shouldn't be used to diagnose obesity in individuals. It proposed confirming excess body fat with at least one other measure, such as waist circumference, waist-to-height ratio or waist-to-hip ratio, or with a direct measure of body fat.

It also proposed dividing obesity into two categories. Preclinical obesity means excess body fat without current signs of organ dysfunction or limits on daily life. Clinical obesity means excess fat that is already causing illness, such as raised blood pressure, fatty liver or breathlessness, or limiting daily activities.

Not every health system has adopted this approach yet. But the direction is clear. Your waist is becoming part of the diagnosis, and doctors are paying more attention to what excess fat is doing to the body, rather than just the number on the scale.

How to measure your waist properly

Many people measure in the wrong place, usually at the narrowest point or where their trousers sit. Here is the method recommended by the NHS and most guidelines:

Stand up straight, with your feet together and your stomach relaxed. Breathe out normally.
Find the bottom of your lowest rib and the top of your hip bone on one side.
Wrap a tape measure around your middle, halfway between those two points. For many people this is close to the belly button, but not always.
Keep the tape snug against the skin but not pressing in, and level all the way around. A mirror helps.
Measure twice and take the average.

Measure at the same time of day, ideally in the morning before eating. Once a month is enough to track change.

Other ways to measure body fat

Bioimpedance scales, which send a small electrical current through the body, estimate body fat at home. They are convenient but can vary a lot depending on hydration, so use them for trends rather than exact numbers.

DXA scans, used in research and some clinics, measure fat and lean mass accurately and can estimate visceral fat.

MRI is the most accurate way to measure visceral and liver fat, but it is mainly used in research.

For most people, a tape measure is the most practical tool, and it costs almost nothing.

The good news about visceral fat

Visceral fat is usually among the first to go when you lose weight. Even a modest loss of 5% to 10% of body weight can noticeably reduce visceral and liver fat and improve blood sugar, blood pressure and cholesterol.

Regular exercise reduces visceral fat even when the scale barely moves. Both aerobic exercise, such as brisk walking, cycling and swimming, and strength training help. This is one reason why a shrinking waist is often the most encouraging early sign when people start being more active.

What drives visceral fat up

Several factors push fat towards the abdomen:

excess calories in general, especially from sugary drinks and ultra-processed foods
alcohol, which adds calories that tend to be stored centrally
short sleep and irregular sleep patterns
chronic stress and high cortisol
inactivity and long hours of sitting
smoking, which is linked to more abdominal fat even though smokers often weigh less
the menopause, when falling oestrogen shifts fat storage from hips to waist
genetics and ethnicity

A practical plan to reduce your waist

Measure your waist and height and calculate your ratio.
If it is 0.5 or above, aim to bring your waist down by 5 cm (2 inches) over the next three to six months.
Cut out sugary drinks and keep alcohol well within guidelines.
Build meals around vegetables, protein and whole foods, with fewer ultra-processed snacks.
Walk briskly for at least 150 minutes a week, and add strength exercise twice a week.
Aim for seven or more hours of sleep.
Measure your waist again once a month.

Visceral fat and your other health numbers

Because visceral fat is so closely tied to metabolic health, a large waist often appears alongside other changes in routine blood tests and checks. Together, these are sometimes described as metabolic syndrome.

A widely used definition, from the US National Cholesterol Education Program and similar international criteria, describes metabolic syndrome as having three or more of the following five features. The International Diabetes Federation version requires a large waist plus at least two of the others:

Waist — Threshold: Above 40 in (102 cm) for men or 35 in (88 cm) for women, with lower cut-offs for people of Asian heritage
Triglycerides — Threshold: 150 mg/dL (1.7 mmol/L) or higher, or on treatment
HDL cholesterol — Threshold: Below 40 mg/dL (1.0 mmol/L) for men or 50 mg/dL (1.3 mmol/L) for women, or on treatment
Blood pressure — Threshold: 130/85 mmHg or higher, or on treatment
Fasting glucose — Threshold: 100 mg/dL (5.6 mmol/L) or higher, or on treatment

Metabolic syndrome roughly doubles the risk of heart disease and greatly increases the risk of type 2 diabetes. It is very common in both the US and the UK.

If your waist-to-height ratio is 0.5 or above, it is worth asking your doctor for a check of blood pressure, fasting glucose or HbA1c, and a cholesterol panel including triglycerides and HDL. Your liver tests may also be worth reviewing, since fatty liver often travels with visceral fat.

The encouraging part is that all five measures tend to improve together when waist size comes down. Many people see their triglycerides fall and HDL rise within a few months of losing weight and becoming more active, often before their weight has changed dramatically. Tracking these numbers alongside your waist gives you a fuller picture of your progress than the scale alone.

How my book can help

The Obesity Exit Strategy explains why fat in the wrong places drives metabolic disease, and how insulin, sleep and stress influence where you store it. It sets out evidence-based strategies across food, fasting, exercise and daily habits. More on the book page.

Frequently asked questions

What is a healthy waist-to-height ratio? Below 0.5, according to NICE. In other words, a waist less than half your height.

Is waist-to-height ratio better than BMI? For predicting diabetes and heart risk in an individual, it often adds information BMI misses. Doctors increasingly use both.

Can you have visceral fat with a normal BMI? Yes. This is common, especially in people of South Asian heritage and in people who are inactive.

What waist size is too big? US guidance flags over 40 inches (102 cm) for men and 35 inches (88 cm) for women, with lower cut-offs for people of Asian heritage.

Can you target belly fat with exercises like sit-ups? No. You can't spot-reduce fat. Overall weight loss and regular exercise reduce visceral fat.

How fast does visceral fat go? It often falls faster than other fat when you start losing weight, which is why waist size can drop quickly at first.

Is waist-to-height ratio useful for children? It is sometimes used for children and teenagers, but cut-offs differ and growth complicates the picture. For children, ask your GP or paediatrician about the right measures.

Does waist size matter if I'm very muscular? Waist-to-height ratio is less affected by muscle than BMI, so it is often more useful for muscular people. A large waist still suggests more abdominal fat.

What if my waist is large but my blood tests are normal? That is still worth acting on. Visceral fat often raises risk before blood tests change, and reducing your waist now can prevent problems later.

How often should I measure my waist? Once a month is enough. Measure at the same time of day and in the same way each time.