William Reville: Overweight but fit is healthier than thin but unfit
Measuring a person’s body-mass index is not the most reliable way of assessing their health
Last year the World Health Organisation warned that Europe is heading for an explosion in rates of excess body weight and obesity, with Ireland on course to become the most obese country in Europe by 2030. Along with the extra weight, we will be carrying the huge extra burden on health (including cardiac disease and diabetes) associated with obesity. Little progress is being made in effectively tackling obesity, but the situation might improve if society were to adopt a more sympathetic attitude towards the obese and provide them with professional psychological assistance to change their eating habits.
We should also stop using body-mass index as the primary classification of body weight or fatness, because it correlates poorly with other health indicators.
People of normal weight generally tend to view obese people as lazy and lacking in resolve. Research has shown (KS O’Brien and others, International Journal of Obesity, March 2013) that anti-fat prejudice is common, for example when assessing job candidates for leadership potential, starting salary and so on. These negative attitudes psychologically debilitate the obese, making it much more difficult for them to effectively tackle their weight problems.
The truth is that obesity is a complex medical problem for which effective treatment is still in its infancy. The urge to eat is an extremely powerful primary drive programmed into humans by evolution in order to ensure our survival.
Throughout most of human evolutionary history, food was very scarce. When we could find food, we ate as much as we could. Human metabolism evolved into a calorie miser: it loves to ingest food calories and hates to spend them. Gaining weight is easy; losing it is not.
Nowadays we all live in the constant presence of food, but our hardwired metabolism continues to prompt us to eat a lot. Although most people learn to control this primary drive, many do not, despite great effort.
We all know people who are intelligent, driven, successful in their careers, capable of great resolve, but who struggle mightily to reduce their weight. The struggle is even more difficult for adults who have overeaten as children.
Current treatments for obesity, although improving, are only minimally effective, and behavioural science and pharmacology still struggle to tame the drive to overeat.
A large proportion of people regain the lost weight at the end of weight-reduction programmes. But we must persevere. Targeted professional psychological help aimed at instilling new eating habits should be made available in a sympathetic environment to all obese people and a big drive must continue to encourage healthy eating in children.
BMI is a ratio between a person’s weight and height, calculated by dividing weight in kilograms by height in metres squared.
Those with a BMI below 18.5 are classified as underweight, 18.5-24.9 as normal, 25-29.9 as overweight, 30-34.9 as grade-one obese, 35-39.9 as grade-two obese and 40 and above as grade-three obese.
But BMI correlates poorly with other health indicators. In the latest study published online by AJ Tomiyama and others in the International Journal of Obesity (February 2016), the authors surveyed more than 40,000 adults, measuring blood pressure, blood fats, cholesterol, glucose, insulin resistance and other markers of cardio-metabolic health.
Then they compared the percentages of metabolically healthy versus unhealthy individuals with their BMI classifications. Nearly half of overweight individuals, 29 per cent of obese individuals and even 16 per cent of grade-two and grade-three obese people were metabolically healthy. And more than 30 per cent of normal-weight people were cardio-metabolically unhealthy.
Using BMI as the main indicator of health misclassifies almost 75 million US adults as cardio-metabolically unhealthy or cardio-metabolically healthy. We should therefore move away from BMI classification and use waist-to-hip circumference ratio measurements instead. A ratio over 0.9 for men and over 0.85 for women flags abdominal obesity and increased health risk.
There is one thing we can do that is guaranteed to help: exercise and become aerobically fit. Aerobic fitness will improve your health at any weight. Overweight but fit beats thin but unfit.
- William Reville is an emeritus professor of biochemistry at UCC. http://understandingscience.ucc.ie