In medical speak we talk, not about being fat, but about overweight or obese. We define being overweight as having a Body Mass Index (BMI) over 25, and obesity as having a BMI over 30. Obesity is usually subdivided into Class 1 obesity (BMI 30-35), Class 2 obesity (BMI 35-40), and Class 3 obesity (BMI greater than 40). Class 3 obesity is usually labeled as severe obesity, and is sometimes unfortunately referred to by the public as “morbid obesity.”
You can calculate your BMI by dividing your weight in kilograms, by your height in meters, and then dividing by your height again. To put it another way for those who prefer pounds and inches, someone 5’9” would be considered overweight if they weighed more than 170lbs, and obese if they weighed more than 203lbs. This theoretical person would be categorized as having severe obesity if they weighed more than 270 pounds.
However obesity is not synonymous with ill health. It is clear that obesity increases the risk of developing insulin resistance, which leads to diabetes, and atherosclerosis. However, someone with obesity need not necessarily develop these problems. In fact, these people are generally termed the metabolically healthy obese.
However, that term may be misleading because, while people may be healthy today, they may not be healthy tomorrow. In a 2017 study published the Journal of the American College of Cardiology, researchers examined electronic health records of 3.5 million people and categorized them according to their body mass index and according to whether or not they had diabetes, high blood pressure or high cholesterol. They were able to compare obese and non-obese patients that were metabolically healthy, i.e. free of these 3 risk factors. In this database, about 15% or slightly over half a million people were categorized as being obese and metabolically healthy.
Over the course of 5 years, obese individuals with none of the 3 risk factors were 49% more likely to develop heart disease, 7% more likely to have a stroke, and 96% more likely to develop heart failure. In absolute terms the increase in heart disease was about 1 extra case per 1000 individuals, which seems small but is important when you apply it to the population as a whole.
In this study, obesity did increase the risk of heart disease long term. However, it is also important to note that the standard risk factors (diabetes, hypertension, and cholesterol) carried a much heavier disease burden. Having one, two, or all three of those diseases increased the number of cardiac events by 5 cases per thousand, 7 cases per thousand, and 10 cases per thousand.
So the answer to the question is essentially yes, people with obesity can still be healthy. However, what this study, and prior research, shows us is that obesity even on its own carries a certain cardiovascular risk even in metabolically healthy individuals. It does however carry less risk than the traditional risk factors of diabetes, high blood pressure and cholesterol. So perhaps the real answer to the question is not whether someone is healthy now, but whether those with obesity will face more health problems down the road. The answer to that question is certainly yes.
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