News Review From Harvard Medical School -- Big Waist Risky Even for Thin Heart Patients
For people with heart disease, having a big waist may be worse than having a high overall weight, a new study suggests. The study put together numbers from 5 earlier studies. Everyone in the studies had coronary artery disease, a narrowing inside the arteries of the heart. The studies included about 15,000 people. Their average age was 66. Researchers measured their body mass index (BMI), a measurement of weight compared with height. They also measured waist-to-hip ratio. This is equal to waist size divided by hip size. Doctors use this measurement to estimate belly fat. Researchers kept track of people for about 5 years. In that time, nearly 4,700 died. People who had a normal BMI but a larger waist were 27% more likely to die than people who were obese but carried less weight in the belly. The Journal of the American College of Cardiology published the study. HealthDay News wrote about it January 31.
By Howard LeWine, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
The current definition of normal body weight based on the very popular body mass index (BMI) has come under attack. New studies suggest that an extra few pounds, as measured by BMI, may not be so bad.
This seems to be especially true for people with coronary artery disease. Those who are overweight or mildly obese actually have longer average survival than those with weight in the normal range (a BMI of 18.5 to 24.9). This is the so-called "obesity paradox."
It's a paradox because people who are overweight are more likely to have high blood pressure and high cholesterol. And they have a greater chance of developing type 2 diabetes. These factors are well known to increase the risk of coronary artery disease. So why would people with heart disease and normal weight have a worse prognosis than overweight and even obese people?
Perhaps we are looking at the wrong measurement. This new study suggests we should pay much more attention to waist size.
The Journal of the American College of Cardiology published the study. Researchers reviewed the medical records of 15,547 people with known coronary artery disease. They were from 3 continents and had a wide variety of ethnic backgrounds. The researchers looked at the links between their BMI and waist-to-hip ratio and their risk of early death.
Waist-to-hip ratio is a way doctors use to estimate belly fat. This is the fat that surrounds our internal organs. Doctors call it visceral fat. Fat that sits in our hips is under the skin. From a health standpoint, this fat is not nearly as harmful as the fat that increases waist size. That's belly fat.
People with more belly fat have a higher risk of developing heart disease, high blood pressure and type 2 diabetes. We still don't know exactly why. A greater waist size means even more than that. According to the results of this study, a greater waist-to-hip ratio translates to a higher risk of early death if you already have heart disease. It is a much stronger predictor than BMI.
In fact, the people with the highest risk of death had a normal BMI but a high waist-to-hip ratio. Their survival was even less than that of obese people with a similar large waist size.
The study was not designed to answer why a person with a "normal" body weight but more belly fat would have the shortest survival. Some possible explanations:
- A lower body weight usually means less muscle mass. So they could actually have a higher percent of body fat than a muscular person with a high BMI.
- Their fitness level was lower than those with higher body weights.
- Other conditions that might shorten survival kept their weight in the normal range.
What Changes Can I Make Now?
We have become used to using BMI to define body weight as normal, overweight or obese. But perhaps we should move it to the back burner and put waist size up front.
I still plan to put my patients on the scale. But I will also measure their waist size and waist-to-hip ratio. I will do this for everyone, no matter how much they weigh.
You don't have to wait to visit your doctor. Just use a tape measure. Measure your waistline at the level of the navel (belly button). Always measure in the same place. Don't suck in your gut or pull the tape tight enough to squeeze the area.
There is no ideal waist size. In general, women should strive for a waist size of less than 32 inches. Men should aim for 35 inches or less. However, height does make a difference.
One simple formula is to divide your height by 2. For example, if you are 6 foot (or 72 inches), half of that is 36 inches. So that's a good target waist size.
To get the waist-to-hip ratio, you also need to measure your hips. Put the tape measure around the widest part. Keep the tape measure level. Now divide your waist size by your hip size.
As with waist size, there is no ideal ratio. An excellent waist-to-hip ratio for a woman is 0.75 or less. For a man, its 0.85 or less. You likely have too much belly fat if you are a woman with a waist-to-hip ratio of greater than 0.9, or 1.0 or greater for a man.
Focus less on what your initial reading is. The most important thing is to work on decreasing waist size or at least not letting it get larger. Regular exercise and avoiding simple sugars are the best ways to reduce belly fat.
What Can I Expect Looking to the Future?
I suspect we will see some changes to the definition of overweight. Perhaps a BMI of 27 or higher makes more sense. It may be best to keep 30 as the definition of obesity.
But, most importantly, we need to start routinely using waist size, waist-to-hip ratio or both to help us define health risk and track our progress.