What Makes Some Thin People 'Skinny Fat'?

We already know that carrying extra fat can come with some serious health risks, including diabetes and cardiovascular problems. But new research suggests that some people with “normal” or “lean” body weights could be at a greater risk for health problems that are typically associated with obesity. In a study published Tuesday in the journal Cell Metabolism, a team of German researchers found that people who are lean but metabolically unhealthy carry a three-fold increased risk of cardiac events, death — or both.

The people in question are those who possess the body type commonly referred to as “skinny fat.” They present as lean but don’t actually exercise or eat well. While such people may appear healthy, they could be at greater risk for the problems associated with obesity than their healthier peers, or even people labeled overweight and obese.

Before we continue, let’s define one of our most important terms: Body mass index (BMI) is a calculation of the ratio of someone’s height to their weight. It’s a crude way of measuring whether someone is a healthy weight given their height. The U.S. Centers for Disease Control and Prevention defines normal weight as 18.5 to less than 25, overweight as 25 to less than 30, and obese as 30 or higher. BMI is a problematic measurement of health since it fails to account for people who have atypical muscle mass or fat compositions.

And as this latest study suggests, it could also fail to be an accurate measure of metabolic health risks for people who have problems that can’t be accounted for by simple body mass.

To conduct this study, the researchers used magnetic resonance imaging and insulin resistance testing to examine 981 subjects, averaging 45 years old, “who were at increased risk of cardiometabolic diseases based upon their weight, a family history of diabetes, a personal history of gestational diabetes (in women), or elevated glucose levels in the non-diabetic range.”

From these subjects, they found a litany of physical characteristics associated with increased risk of death (all-cause mortality, as doctors call it) and cardiac issues in people who are a normal weight. These characteristics, the study’s authors say, make up “metabolic syndrome”:

•Fatty liver

•Visceral obesity (a large concentration of fat around the torso)

•High percentage subcutaneous — under the skin — abdominal fat mass (ratio of subcutaneous abdominal fat to total fat mass)

•Low percentage subcutaneous leg fat mass (ratio of leg fat to total fat mass)

•Insulin secretion failure and insulin resistance (which predict diabetes and heart disease)

•Low cardiorespiratory fitness

•Increased carotid intima-media thickness (a measure of carotid atherosclerotic vascular disease)

So what does this all mean?

“We considered our subjects metabolically healthy when fewer than 2 parameters of the metabolic syndrome were present,” write the authors. In other words, even if a person falls within a normal BMI range, if they express two or more of these characteristics, they could be at a seriously increased risk of cardiovascular events or early death.

The researchers say that this evidence suggests that these skinny fat people could be expressing a type of lipodystrophy, a condition in which fat is not stored in the body as it normally would be. As such, these lean people, who may otherwise appear to be physically fit, are in fact at risk in terms of their metabolic health.

This study shouldn’t cause you to fly into a panic about your health, but it should emphasize the need for exercise and proper diet, even if you’re one of those people who can seemingly eat anything they want and not gain a pound.

Abstract: A BMI in the normal range associates with a decreased risk of cardiometabolic disease and all-cause mortality. However, not all subjects in this BMI range have this low risk. Compared to people who are of normal weight and metabolically healthy, subjects who are of normal weight but metabolically unhealthy (20% of the normal weight adult population) have a risk greater than 3-fold higher of all-cause mortality and/or cardiovascular events. Here we address to what extent major risk phenotypes determine metabolic health in lean compared to overweight and obese people and provide support for the existence of a lipodystrophy-like phenotype in the general population. Furthermore, we highlight the molecular mechanisms that induce this phenotype. Finally, we propose strategies as to how this knowledge could be implemented in the prevention and treatment of cardiometabolic diseases in different stages of adiposity in routine clinical practice.