Global rates of obesity have increased dramatically in the last 4 decades.
Body mass index (BMI) is used to evaluate a person's status as under- or overweight. BMI is calculated as kilograms of weight per meter squared (kg/m²).
BMI for a normal weight is 18.5-24.9. A BMI under 18.5 is considered underweight, over 25 is overweight, over 30 is obese, 35 is severely obese and morbidly obese is over 40.
If you know your height and weight, you can use an online calculator to work out your BMI.
Number of people with obesity up from 105 million to 641 million
Researchers for the Non-Communicable Disease (NCD) Risk Factor Collaboration have carried out a major global report on human weight trends.
They analyzed data from 1,698 population-based studies, surveys and reports from 186 countries, representing 99% of the world's population.
Statistics were available for 19.2 million men and women aged 18 years and over.
Findings show that in the last 40 years, the prevalence of obesity worldwide has risen from 105 million in 1975 to 641 million in 2014. Meanwhile, the global percentage of people who are underweight fell by about a third. In 1975, 13.8% of men and 14.6% of women were underweight; in 2014, the figure was 8.8% for men and 9.7% for women.
After adjusting for age, the proportion of men who are obese has more than tripled from 3.2% to 10.8%, and the proportion of obese women has more than doubled, from 6.4% to 14.9% since 1975.
A comparison of BMI reveals that on average, each member of the world's population became 1.5 kg heavier every decade.
If the rate continues to increase, 18% of men and 21% of women globally will be obese. Moreover, 6% of men and 9% of women will be severely obese, with a BMI of over 35.
The researchers caution, however, that these figures should not distract from the problem of excessively low body weight that continues to trouble the world's poorest regions.
Almost 25% of the population of south Asia, and over 15% of men and 12% of women in central and east Africa, are still underweight.
44% of Americans could be obese by 2025
Here are some of the main results of the research:
- Among the wealthier nations, the US has the highest BMI for both men and women, at over 28. More than 25% of severely obese men and almost 20% of severely obese women worldwide live in the US. Predictions indicate that by 2025, 43% of women and 45% of men in the US will be obese
- The highest average BMI in the world is in the island nations of Polynesia and Micronesia, at 34.8 for men and 32.2 for women in American Samoa. In Polynesia and Micronesia, more than 38% of men and over 50% of women are obese
- Almost 20% of the world's obese adults and over 27% of severely obese adults live in just six countries: Australia, Canada, Ireland, New Zealand, the UK and the US
- Women in Singapore, Japan and France barely increased their average BMI over the 4 decades
- The lowest average BMI was found in Timor-Leste, Ethiopia and Eritrea. Timor-Leste had the lowest average BMI for women at 20.8, and Ethiopia had the lowest rate for men, at 20.1.
Senior author Prof. Majid Ezzati, from the School of Public Health in Imperial College London in the UK, warns that at present rates, there will be more severely obese women by 2025 than underweight women.
Prof. Ezzati says:
"To avoid an epidemic of severe obesity, new policies that can slow down and stop the worldwide increase in body weight must be implemented quickly and rigorously evaluated, including smart food policies and improved health care training."
Prof. George Davey Smith, from the MRC Integrative Epidemiology Unit, School of Social and Community Medicine in Bristol, UK, entitles his linked comment, "A fatter, healthier but more unequal world."
He highlights the fact that in high-income countries, obesity is a major and growing problem, while undernutrition still poses a challenge for low-income countries, with major health implications for children born to seriously underweight women.
He warns that in the urgency of dealing with obesity, we must not forget the "substantial remaining burden of undernutrition."
Focusing on obesity, he cautions, may divert resources within poorer countries away from the poorest individuals to the wealthier members of those societies.
Medical News Today recently reported that many parents who consume a high-fat diet may be putting their offspring at risk of obesity.