In a recent JAMA article, German researchers investigate if there can be such a thing as a healthy obese person. The results show that obese individuals defined as metabolically healthy do not have increased risk of heart disease or mortality. In fact, almost 40% of a US based and 20% of a UK based population database of individuals with obesity were found to be metabolically healthy. This is a very helpful way to identify those who are healthy but obese instead of using the Body Mass Index (BMI). We'll clarify everything so you walk away with a new understanding of what healthy means.

Study

In a recent JAMA article, German researchers investigate if there can be such a thing as a healthy obese person. To do this they had to pick some complications of obesity to measure against. The Authors decided to review heart disease and mortality. The study database was the National Health and Nutrition Examination Survey (NHANES-III) and the findings were validated with the independent database of the UK Biobank cohort, a population based prospective study. The study was conducted for the years 2015-2016.

Results

A total of 12,341 individuals were analyzed with an average age of 42 years old, equally split between men and women with an average follow up of 14.5 years. The best predictors of heart disease and total mortality were systolic blood pressure and waist-to-hip ratio. To figure out if you can be obese but still 'metabolically healthy', the researchers found a cutoff for blood pressure and another cutoff for waist-to-hip ratio that statistically was a valid threshold below which they could safely define someone as metabolically healthy--this would be a subgroup of obese individuals who are NOT at increased risk of mortality (with a 95% confidence interval). Before we reveal what it takes to be metabolically healthy, we need to define several terms in these results to better help the reader understand what is going on.

Body Mass Index (BMI)

Source: CDC.gov

We've all heard of BMI in some capacity. It is one way to measure how obese someone is given the large variations of height in the population. In other words a 200 lb 5'6'' tall person is more obese than a 200lb 6'1'' tall person. BMI is calculated as the weight in kilograms divided by the height in meters squared. A BMI more than 30 is the cutoff for obesity.

Ignore the commercials from deodorants to clothing that advertise beautiful and healthy at any weight. They are trying to sell product to a larger audience because more than two-thirds of US adults are overweight or obese, so there are more people to sell to. However, being obese is correlated with several complications that end up shortening one's life. Having said that, we have seen overweight or obese individuals who ARE healthy and live to a very old age, sometimes longer than their over-stressed doctors. Hence, the BMI is great as an initial benchmark, but we need another measurement tool to tell us who are obese but metabolically healthy.

Confounders

There are so many variables that describe an individual patient. How can we be certain that things like being married or having a college degree have an effect on whether you are obese and healthy or obese and unhealthy? To do that, the researchers controlled for the following variables: sex, race/ethnicity, educational level, income, marital status, smoking status, alcohol consumption, and physical activity.

Systolic Blood Pressure

When you get your blood pressure measured at the doctor's office or if you have an at-home blood pressure automatic gauge (placed around the bicep or the wrist), you will notice two numbers such as 120/80 mmHg. The top number is the systolic blood pressure (SBP) which measures the force your heart pumps blood out into the arteries with each beat. This is also the first 'thump' sound heard when a clinician uses a stethoscope to listen to your artery after releasing the pressure from a manual blood pressure guage.

The bottom number on the other hand is the diastolic blood pressure (DBP) which measures the smaller force when your heart muscles relaxes and your heart ventricle refills with blood between beats. With a stethoscope, this is when the loud thump sound of the systolic pressure significantly drops.

When you have narrowing of the arteries because of smoking, alcohol, unhealthy food choices, among other factors, the SBP number goes up because it takes more force to push through a narrower tube filled with plaque or because of stiffer arteries that don't expand. When you have chronic unhealthy habits over a long time--eventually the structure/shape of your heart muscle changes so that it doesn't expand as normally as it would between beats which then causes the DBP to stay elevated.

Metabolically Healthy Obesity (MHO) Criteria

The criteria used surprisingly ended up classifying 40% of individuals with obesity in the NHANES-III population (which is representative of the US population) as metabolically healthy! In the UK based Biobank database, only 20% of individuals with obesity were metabolically healthy.

The criteria for metabolically healthy are:

  • Systolic Blood Pressure < 130 mmHg without the use of blood pressure medication
  • Waist-to-Hip Ratio (WHR) <0.95 for women and <1.03 for men
  • No prevalent diabetes
  • All criteria must be met. Note that in the study, the researchers found that these criteria accurately describe someone who is obese AND healthy but only at BMI<40. After BMI>40 being metabolically healthy does start to show risk of heart disease and mortality even though it's still less than metabolically unhealthy individuals also with a BMI>40. What this tell us is that after that point, it becomes very hard for the body to maintain a metabolically healthy profile and one can imagine that if the study authors followed these folks for another 10 years-- they would likely quickly move from metabolically healthy to metabolically unhealthy because of the physiological changes associated with a larger BMI.