Is being overweight healthy and a predictor of longer life? In contrary to well established notion of a healthy weight, recently published studies have shown us another side of this picture and introduced a phenomenon generally known as the “obesity paradox”. In simple words, this paradox means that overweight people are healthier than normal weight people.
Let us first define – what is obesity? Public health professionals and physicians use a term called body mass index (BMI), which is a measure for human body shape based on an individual’s weight and height. It is calculated by weight in kilograms, divided by square of height in meters. A healthy BMI is considered to be above 18.5 and below 25. Overweight people usually have a BMI between 25 and 30. Someone with a BMI of ≥30 is classified as being obese or simply fat. Over the last few decades, obesity has been known as a risk for cardiovascular disease. And there have been lot in public health guidelines to reduce the body weight.
However, there is evidence in scientific literature that being overweight can lead to a longer life. A recent study involving nearly 2.9 million people reported a 6% decreased risk of death for people who were overweight (BMI 25-30) than those considered to have a healthy weight. Moreover, mildly obese people (BMI 30-35) had similar risk of dying as the healthy weight people. The conclusion of this large scale study was that “overweight is associated with significantly lower all-cause mortality”.
But is it the full picture and the benefits of gaining weight in regard to longer survival well-founded? Probably not. The main criticism of all studies which have shown a beneficial effect of increased weight with reduced mortality is that they might not have taken good care of other risk factors when reporting their results. This makes it difficult to prove independent associations between weight gain and mortality. For example, the information about the numbers of years spent free of ill-health in people across different BMI categories would help to better understand the association of overweight and mortality. It might be possible that overweight people get an early medical treatment such as to control blood pressure, cholesterol, and a strict check on diabetes status. This, in turn, helps to keep a favourable cardiovascular profile.
The change in other risk factors such as smoking, healthy eating and physical activity could also affect the body weight association with mortality. The evidence of this came from a study that reported the association of body weight and mortality in people who quit smoking. People who quit smoking had lower risk of heart disease even they had a significant gain in body weight. So, it does not mean that increase in body weight resulted in reducing the risk of heart disease. The health gains from giving up smoking were the main reason for a lower risk of having heart disease.
Another study to explain the obesity paradox reported that people can be obese yet physically healthy and fit and at no greater risk of heart disease or cancer than normal weight people. Being physically active and having a higher fitness were more important than being overweight in this study.
Still, the so-called obesity paradox exists, and we have not yet understood it. However, we should be very careful when interpreting the benefit of being overweight for long survival. So far, the advice to people is to keep a healthy weight by healthy life style factors, such as physical activity, quit smoking and healthy eating.
Javaid Nauman, post doc at CERG.