Scientists Find Different Types of Obesity, Confirming High BMI Doesn’t Always Signal Health Risks

Photo credit: RyanJLane - Getty Images

Photo credit: RyanJLane – Getty Images

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  • According to a new study published in Nature Metabolism, obesity is not just a matter of weight in relation to height or body mass index (BMI)—there are actually at least four metabolic body types.

  • The research also found that those who fit in the BMI category of overweight or obese are not destined to develop diseases previously thought to be directly related to weight.

For decades, one calculation, body mass index (BMI) has been used to determine if someone is overweight or obese. BMI compares weight in relation to height and when that number is high, doctors will likely tell patients that they’re at risk for health problems and therefore, need to lose weight.

Turns out, though, that this equation isn’t a reliable marker of health outcomes. Some people who fit the “obese” category, according to BMI, may never receive a disease diagnosis, while others in the “normal” BMI range could have a genetic predisposition to heart disease and other illnesses, no matter their weight.

“It has long been clear to us that there are at least three types of people when it comes to obesity: Those who are healthy and obese, those who are obese and have co-morbidities, such as diabetes or heart disease, and those who are obese and on their way to developing co-morbidities,” Andrew Pospisilik, Ph.D., chair of the Department of Epigenetics and a founding member of the Metabolic and Nutritional Programming Group at the Van Andel Institute in Grand Rapids, Michigan tells Bicycling. “We wanted to see if we could begin to identify the genetic variations in these different ‘types’ of obesity.”

To examine the types of obesity, Pospisilik and his team studied twins and the ways in which their weight varied over the years. Then, they tried to mimic their findings in mice.

“Using a purely data-driven approach, we saw for the first time that there are at least two different metabolic subtypes of obesity, each with their own physiological and molecular features that influence health,” Pospisilik said. “Our findings in the lab almost carbon copied the human twin data. We again saw two distinct subtypes of obesity.”

Until now, scientists placed people in one of three metabolic types: endomorph (stores fat easily), mesomorph (easily gains muscle), and ectomorph (thin, struggles to gain fat or muscle). The recent findings, though, published this month in Nature Metabolism, divides people into four metabolic subtypes (two prone to leanness and two prone to obesity) that may one day help doctors provide more precise care for patients and inform more precise ways to diagnose and treat obesity and associated metabolic disorders, Pospisilik explained.

The team also found that of the two metabolic subtypes prone to obesity, one was associated with increased inflammation, which can elevate the risk of certain cancers and other diseases, while the other wasn’t. It also appeared that some genes responded to certain triggers—such as lifestyle choices or specific foods—leading to weight gain and a susceptibility to disease, while others did not.

The science of studying of how genes are affected by behavior and environment is called epigenetics. Pospisilik, an epigeneticist, doesn’t study, for example, which foods or lifestyle choices can alter a person’s weight, but instead looks for genetic predispositions that coordinate to weight and how that can play into disease.

Unlike genetic alterations, epigenetic changes are reversible and do not change the DNA sequence. “I like to tell people that all bees are born with the same DNA, but some bees become worker bees and others become queen bees. In the end, all queen bees are genetically like other queen bees. How does that happen? Epigenetics are the processes that can guide the same bee DNA to develop into a queen or a worker, but nothing in between,” Pospisilak said.

Pospisilak and his team found that this same idea applies to humans and their weight and health. While one person is more prone to muscle building, another might be more prone to weight gain, and their diets may be very similar.

“Between twin studies and mice studies, we can really show how each individual might have several genetically pre-programmed paths available, with lifelong consequences,” Pospisilak explained.

In the end, the new research confirms that there’s more to health and fitness than the number on the scale or on a BMI chart.

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