People with metabolically obese normal-weight (MONW) phenotypes have very little jiggly fat. Instead, they store most of their fat inside the abdominal cavity and around the internal organs, which is far more dangerous because of its links to cardiovascular disease, type-2 diabetes, and even death. Get more insight into the dangers of MONW, why it’s more common among Asian men, and how to keep it under control through our interview with Dr Micheal MacDonald, senior consultant cardiologist from the Harley Street Heart and Vascular Centre.

Q: How can a thin person be fat, what is the metabolically obese normal-weight (MONW) phenotype?

The MONW phenotype describes someone who looks to be of normal body weight and has a normal, or lower, body mass index (BMI) but who actually has unhealthy amounts of hidden visceral fat. Normal BMI for Asians is defined as <24 or 23kg/m2.

We store two basic types of fat two ways. Subcutaneous fat is stored just beneath the skin, more or less evenly around the body, and is the visible/ pinchable fat that forms love handles and spare types. The other type of fat is visceral fat, which is stored deep inside the body, particularly around the organs (liver, intestines, etc). If people, particularly men, are overweight and also have a high proportion of visceral fat, they tend to have large, firm, distended bellies; often called beer bellies or apple body types. However, people who are MONW phenotypes have very little subcutaneous fat and seem to store nearly all their fats as visceral fat where it’s not visible or pinchable, but far more dangerous. In recent years, medical science has realised that fat, especially visceral fat, is not inert, but metabolically active.

Q: Does science know why Asians have more MONW than Westerners?

The underlying cause of MONW is not yet fully understood; in fact it was only in the last few decades that medical science recognised the significant differences in body fat content and distribution between East Asians, South Asians, and Caucasians. The distribution of body fat is markedly different between ethnic groups, and at any given level of adiposity, Asians have a much greater predisposition to risk of cardiometabolic disorders than Caucasians.

Q: What makes visceral fat more dangerous than the subcutaneous fat?

Visceral fat is strongly linked to metabolic disease, insulin resistance, and an increased risk of death, even in people with normal BMI. It also doesn’t carry the same risks as subcutaneous fat, and is more likely to promote 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. The more we study fat, the more active it appears to be.

Q: How do doctors detect visceral fat or decide whether someone is a MONW phenotype?

The only accurate way to exactly measure the the amount of visceral fat in a person is with a CT or MRI scan. There are several types of bioelectrical impedance devices which can indicate excess visceral fat, but with less accuracy. However, in most cases a visual and physical examination is enough for a doctor to suspect excess visceral fat. If a person has a BMI of over 25 for Caucasians or over 23 for Asians and also have a large waist size, they almost certainly have too much visceral fat.

As for MONW patients who are not visibly fat, we rely on the metabolic indications of obesity to diagnose them. Blood tests indicating elevated triglycerides and reduced levels of high-density lipoprotein cholesterol (“good cholesterol”), as well as elevated blood pressure and lower physical activity expenditure could suggest high visceral fat levels.

Q: If someone is diagnosed as a MONW phenotype or as being insulin resistant does that mean they will inevitably develop type 2 diabetes, or can it be prevented?

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 lifestyle changes. A healthy diet and regular exercise can prevent type 2 diabetes because they can reverse insulin sensitivity and reduce visceral fat levels in even MONW patients. A healthy diet and regular exercise are also the best tools for preventing the onset of cardiovascular disease, or managing it if you have developed it.

Q: Does the MONW phenotype run in families?

While the fact that the MONW phenotype is far more common among Asians indicates a genetic factor, there is not yet any indication that it’s hereditary. The role of genetics in how our bodies store and manage fat is currently the subject of much research around the world so we might know the answer soon.

Q: If we can’t see it or detect it on scales, are there signs that indicate too much visceral fat?  

For most people, the most obvious indicators of visceral fat are a high BMI and large waist. For an average height person, anything over 36 inches or 92cm is probably a sign you should lose some weight. MONW phenotypes have no visible clues but if have been feeling unusually tired, have started to urinate more frequently, or are often thirsty, it is worthwhile mentioning it to you doctor.

Q: What are the signs that indicate insulin resistance?

Frequent urination and thirst are possible indicators of insulin resistance, and hence also MONW. Other signs to look out for are feeling hungry shortly after meals, tingling sensations in the hands/ feet, increased fatigue, and frequent/ persistent infections.

Q: Can we reduce visceral fat with diet and exercise like we can subcutaneous fat?

Visceral fat can definitely be reduced with diet and exercise, even in MONW phenotype people. In fact, some research indicates that it’s more responsive to diet and exercise than subcutaneous fat.


Dr Michael MacDonald from The Harley Street Heart and Vascular Centre

Dr Michael MacDonald from the Harley Street Heart and Vascular Centre

Dr Michael MacDonald is a senior consultant cardiologist at the Harley Street Heart and Vascular Centre in Gleneagles Hospital, Mount Elizabeth Novena Hospital, and Mount Elizabeth Medical Centre.



Main photo image by Dreamstime.