We typically think of obesity as being a risk for a number of health problems and a marker for poor metabolic health. Then along comes research suggesting not all people who are significantly overweight or obese are unhealthy from a metabolic standpoint. For example, some significantly overweight and obese people have normal blood pressure and a cholesterol and blood sugar level that falls within the normal range.
Researchers have dubbed people who fall into this category “metabolically healthy obese,” meaning they have no obvious metabolic abnormalities like abnormal blood pressure, lipids or blood sugar that put them at greater risk for heart disease or type 2 diabetes. Up to 30% of obese people fall into this category.
Obese and Metabolically Healthy – Truth or Myth
A new study published in the Journal of Clinical Endocrinology and Metabolism shows people who are metabolically healthy and obese may STILL be at higher risk for health problems despite having no documented metabolic abnormalities. To reach this conclusion, researchers followed over 5,000 people, white or Mexican-American between the ages of 25 and 64, who were obese but free of heart disease or type 2 diabetes, for over seven years.
Participants were deemed metabolically healthy if they had no more than one metabolic abnormality and were classified as metabolically unhealthy if they had two or more metabolic abnormalities. The metabolic factors they measured included blood sugar level, triglycerides, blood pressure, HDL-cholesterol and markers for insulin resistance. They also followed normal weight participants who were metabolically healthy and unhealthy during the course of the seven-year study.
What did they find? The study showed both metabolically unhealthy participants of normal weight and metabolically healthy obese participants were at greater risk for heart disease and type 2 diabetes compared to metabolically healthy people of normal weight. In fact, metabolically healthy obese participants were at four times greater risk for heart disease and type 2 diabetes compared to those of normal weight who were healthy from a metabolic standpoint.
Based on this study, experts believe even metabolically healthy people who are significantly overweight or obese will eventually become metabolically unhealthy and their risk for health problems like type 2 diabetes and heart disease will go up. In fact, in this study, the risk for type 2 diabetes went up incrementally with an increase in BMI.
The take-home message? Being obese and metabolically healthy now doesn’t mean you’ll remain free of metabolic problems that put you at risk for health issues like heart disease and type 2 diabetes.
Why Is Obesity Linked with a Greater Risk for Heart Disease?
One theory is that insulin resistance, more common in people who are obese, is a driving force for the development of atherosclerotic heart disease. Insulin resistance is a state where cells don’t respond to the insulin produced by the pancreas as well as they should so the pancreas has to pump out more insulin. Insulin resistance fuels production of blood triglycerides, another risk factor for heart disease. Plus, hypertension is three times more common in obese people relative to people of normal weight. High blood pressure puts added strain on the heart, forcing it to pump harder to push against the added resistance. This can eventually cause the chambers of the heart to dilate and not pump blood as efficiently. This is called a dilated cardiomyopathy, and hypertension is a common cause.
There’s growing evidence that systemic inflammation plays a role in the development of atherosclerotic heart disease. Adipose tissue, particularly visceral adipose tissue that lies deep in the pelvic cavity, releases a number of inflammatory molecules that cause systemic inflammation and inflammation inside blood vessels. This chronic inflammation damages blood vessel walls and increases the risk of blood clots forming that reduces blood supply to the heart. In addition, people who are obese produce less of a compound called adiponectin that helps to keep inflammation in check.
Preliminary research also suggests that inflammation plays a role in the development of type 2 diabetes, possibly by damaging beta cells in the pancreas that produce insulin. Inflammation is a factor in the development of some types of cancer, and research shows obese people are at higher risk for cancers of the uterus, breast, colon, esophagus, pancreas, kidney, gall bladder and thyroid gland.
The Bottom Line?
Obese and metabolically healthy? Not necessarily. It’s possible that a sub-group of mostly younger people who are obese are metabolically healthy but still at greater risk for transitioning into a metabolically unhealthy state. When this happens their risk for type 2 diabetes and heart disease goes up. There are lots of good reasons to maintain normal body weight – for metabolic health and for overall health and wellbeing.
References:
Medscape.com. “Metabolically Healthy Obesity” is Not Benign.
Curr Pharm Des. 2013;19(32):5678-83.
Circulation.1997; 96: 3248-3250.
LiveScience.com. “Insulin Resistance: Risk Factor for Heart Disease and Diabetes”
Circulation Research. 2005; 96: 939-949.
J Cell Biochem. 2013 Mar;114(3):525-31. doi: 10.1002/jcb.24402.
National Cancer Institute. “Obesity and Cancer Risk”
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