Scientists speak out about metabolically unhealthy BMI and heart risks

Camille Bienvenu
Mon, 07 Aug 2017
Scientists speak out about metabolically unhealthy BMI and heart risks
New research sheds light on the "metabolically unhealthy" phenotype seen in the non-obese population that raises the risk for conditions such as heart disease, stroke and type 2 diabetes.

Is leanness necessarily a sign of good health? That's the question researchers from the University Hospital Tübingen and the Helmholtz Zentrum München, in Germany, have studied.

What is referred to as the "metabolically unhealthy" phenotype represents about 20 per cent of adults with a normal weight and corresponds to a set of factors that individually and in combination elevate risks for cardiometabolic diseases.

These factors include things like body fat distribution and visceral fat, but also abnormal lipids, blood sugar levels, glucose tolerance, mitochondrial dysfunction as well as insulin dysfunction.

Most of these parameters also happen to be common characteristics of the metabolic syndrome. In the study, researchers actually define "metabolically healthy" as having less than 2 risk parameters of the metabolic syndrome.

The latest study has found that people who are of normal weight but metabolically unhealthy by those standards have a more than three-fold higher risk of heart complications and/or death.

In some respects, this risk is also even higher than that so-called "metabolically healthy obese" individuals are exposed to.

Those with the metabolic healthy obesity phenotype only have a moderate (25%) higher risk of all-cause mortality and/or heart events, while the risk appears to be much higher (300%) in metabolically unhealthy lean people.

Scientists knew from previous research that a near normal body mass index (BMI) - defined by the WHO as comprised between 18.5 and 25.0 kg/m2 - associates with the lowest risk of death from all causes.

Whether this applies to everyone remained to be shown. In recent times, a research team at the University of Birmingham's Institute of Applied Health Research highlighted that the risk of cardiometabolic diseases and death can vary substantially.

Upon analysing data from 981 participants, the German researchers found that 18% of lean people were considered metabolically unhealthy.

Of all factors looked at, including body fat mass, deposition of fat in the liver, insulin sensitivity, arterial thickness and fitness, a reduced accumulation of subcutaneous fat in the lower body of those with a normal BMI is what puts them most at risk.

This makes sense as we know that a high volume of visceral fat, especially in the abdominal region, can worsen the cardiometabolic profile and may therefore be more reflective of risk than BMI or waist circumference.

In contrast, in obese individuals, nonalcoholic fatty liver disease and increased abdominal fat mass are the two factors that strongly determine cardiometabolic risks.

Based on these findings, early detection for metabolic diseases in lean subjects could one day focus on impaired fat storage in the lower body to reduce risks.
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