The current definition of a healthy body mass index (BMI) has been under some scrutiny after a new research study found that the BMI we consider “normal” may actually be too low and unhealthy.
A recent study collected data and adjusted results using a wider range of potential confounders (other variables) than in prior studies looking at measuring and interpreting BMI. The new data showed the impact of newer treatments to reduce cardiovascular disease illness and death while past studies relied on data from earlier times when less cardiovascular disease protection occurred. The current study included people from lower-income countries, although the finding is just as applicable to people who live in high-income countries, who were also included in the study population, noted Salim Yusuf, MBBS, principal investigator for the study.
The study showed that middle-aged adults with a body mass index of 25-29 kg/m2 (currently considered “overweight”) had a significantly better adjusted survival during an average follow-up of nearly 10 years than did people with a “normal” body mass index of 20-24 kg/m2 in a worldwide study of more than 140,000 people. This suggests that the current, widely accepted definition of normal body mass index is wrong.
This is where other tools come into play that can be better predictors for survival. One is the ratio of hand-grip strength to body weight. This assesses the importance of muscle mass to overall weight. The optimal strength/weight ratio is 0.42 in women and 0.50 in men according to Dr. Darryl Leong, a cardiologist at McMaster University and the Population Health Research Institute, both in Hamilton, Ont.
In a large longitudinal population study, it was found that grip strength measurement can be a strong predictor of cardiovascular mortality and a moderate strong predictor of cardiovascular disease. This new study, called the Prospective Urban-Rural Epidemiology Study (PURE) included about 140,000 people that were examined between 2003-2009. Grip strength was measured using a hand grip dynamometer.
Another very important and good predictor of weight is the waist/hip ratio which adds the dimension of the location of body fat rather than just the amount. An optimal waist/hip ratio for survival according to Dr. Leong is 0.83 in women and 0.93 in men. This means that a man whose hand/grip strength (in Kg) is half of the person’s body weight, then his chance for survival is very good.
So even though being “overweight” according to the BMI readings we currently use seems to lower mortality rates, we need to remember that the link between total mortality and BMI was strongest in the group of people that were on 1 or more treatments aimed at preventing cardiovascular disease (which may include being on a Statin drug or anti-hypertensive med) while there was no benefit among people not receiving any cardiovascular disease preventative measures.