Watch out for diabetes, even if you have a normal BMI
Many people with diabetes or pre-diabetic symptoms are lean and have BMIs in the normal range
There has been a rise in obesity rates and associated medical complications - such as type 2 diabetes - during the past two or three decades across Asia.
But there are also many people with diabetes or who have pre-diabetic, insulin-resistant symptoms that weigh in the normal range and show off normal BMIs (body mass indexes) - yet their bodiesbehave as if they are obese.
Doctors have coined the phrase metabolically obese normal weight (MONW) phenotype for this group of people.
It refers to lean subjects with metabolic dysfunction typically observed in obese people and is associated with an increased risk of diabetes.
The problem with the MONW phenotype is not the total amount of fat on the person's body but where the fat is stored.
MONW people do not store fat subcutaneously (beneath the skin) as visible love handles and spare tyres. Instead they store it as visceral fat, around organs such as the liver, where it is far more dangerous.
The MONW phenotype in Asians is associated with a 4.5 to 8.5-fold increased risk for developing type 2 diabetes, and MONW subjects have a greater risk for cardiometabolic disease not only compared with metabolically healthy "lean" subjects but also with metabolically healthy "obese" subjects.
Almost 40 per cent of newly diagnosed type 2 diabetes in Asians occurs in MONW phenotypes, and these individuals are likely to go undiagnosed until they develop a serious cardiometabolic disease.
Dr Michael MacDonald, a senior consultant cardiologist with Harley Street Heart & Vascular Centre at Mount Elizabeth Medical Centre, sheds more light on this condition.
What makes visceral fat more dangerous than visible subcutaneous fat?
Visceral fat is strongly linked to metabolic disease and insulin resistance, and an increased risk of death - even for people with normal BMI.
Subcutaneous fat does not carry the same risks as visceral fat, which is more likely to raise the risk for serious medical conditions such as heart disease, Alzheimer's, type 2 diabetes and stroke.
Visceral fat is sometimes called "metabolically active fat" because it actively affects the production and function of certain proteins and hormones.
These include proteins that cause inflammation of the body's tissues and organs and the narrowing of blood vessels and others that can increase insulin resistance, which can lead to glucose intolerance and type 2 diabetes.
How do doctors detect visceral fat or decide whether someone is a MONW phenotype?
The only really accurate way to exactly measure the amount of visceral fat a person has is with a CT or MRI scan. In the case of MONW patients, we rely on the metabolic indications of obesity to diagnose them.
Blood tests indicating elevated triglycerides and reduced levels of high-density lipoprotein cholesterol, the so-called "good cholesterol", could be an indication of high visceral fat levels. Elevated blood pressure and a lower physical activity energy expenditure are also indicators.
If you notice yourself feeling unusually tired, or have started to urinate more and or are often thirsty, it is worthwhile mentioning it to your doctor.
Other signs to look out for include feeling hungry again shortly after meals, tingling sensations in hands or feet, feeling more tired than usual and frequent or persistent infections.
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If someone is diagnosed as a MONW phenotype, does that mean he will inevitably develop type 2 diabetes? Or can it be prevented?
No, type 2 diabetes is not inevitable. Rather, being diagnosed as insulin-resistant or being a MONW phenotype should be considered a wake-up call that you need to make some lifestyle changes.
A healthy diet and regular exercise can prevent the development of type 2 diabetes. Diet and exercise can increase insulin sensitivity and reduce visceral fat levels in even MONW patients.
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