Worldwide obesity has more than doubled since 1980, according to the World Health Organization. And without sufficient evidence on physical activity, it's hard to say how much activity people are really getting on a daily basis and how those activity levels affect obesity numbers.
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But a new global study from Stanford University used a "simple and convenient way" to track the physical activity of 717,000 men and women from 111 countries: smartphones.
Researchers used steps tracked in participants’ phones for an average of 95 days each (68 million days’ worth of minute-by-minute data) to determine whether average steps directly correlated with their obesity levels.
Instead, they found each country’s “activity inequality,” or the gaps between people who walk more than others, was a much better predictor of obesity levels.
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"If you think about some people in a country as 'activity rich' and others as 'activity poor,' the size of the gap between them is a strong indicator of obesity levels in that society," Scott Delp, bioengineer and study author, said in a Stanford news release.
Scientists used the Azumio Argus app, which tracks physical activity and health behaviors such as height, weight, age and gender.
They focused on data from the 46 countries where Azumio provided the most data (at least a thousand anonymized users).
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The research, published in the journal "Nature," shows strong correlations among activity inequality, the gender-activity gap and obesity levels.
How many average steps do residents of each country take each day?
Overall, the average number of daily steps was 4,961, but that number varied across the world.
In Hong Kong, participants averaged 6,880 steps a day, placing the country at the top of the list. Others near the top include China (6,189 steps), Japan (6,010), Spain (5,936) and the United Kingdom (5,444).
The United States fell slightly below average, clocking in 4,774 steps a day. Mexico had similar numbers.
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But Indonesia sat at the bottom of the ranking with an average 3,513 steps a day.
Other countries at the bottom: South Africa, India, Malaysia and Saudi Arabia.
High activity inequality and its effects on obesity
The number of average steps for each country, the study found, wasn’t directly correlated to the country’s obesity levels.
Instead, active inequality gaps (gaps between people who move most vs. those that move least) made for better predictors for obesity levels in each country.
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For example, Sweden, which had one of the smallest activity inequality gaps, also had the smallest disparity between gender-activity gap (difference between number of male steps vs. female steps) and one of the lowest rates of obesity.
The United States, on the other hand, was fourth-last in overall activity inequality, fifth from the bottom in the gender step gap and had the highest number of overweight and obese people in the world.
Compare that with Mexico, which had similar average steps, but lower activity inequality and obesity levels.
The countries with the highest and lowest activity inequality
Top five highest activity inequality
- Saudi Arabia
- Autralia
- Canada
- Egypt
- United States
According to the Organisation for Economic Co-operation and Development, the United States, Australia and Canada are all among the top 10 countries with the highest obesity among adults.
Top five lowest activity inequality
- Hong Kong
- China
- Sweden
- South Korea
- Czech Republic
Additional findings
The researchers also found the more walkable and pedestrian-friendly cities had lower activity inequality levels.
And when it comes to the gender step gap, the team found great variations in countries, negatively impacting women.
“When activity inequality is greatest, women’s activity is reduced much more dramatically than men’s activity, and thus the negative connections to obesity can affect women more greatly,” computer scientist and study author Jure Leskovec said in a Stanford news release.
Researchers hope the large-scale study offers insight into where efforts could be invested and policies could be changed to provide the largest impact on the public health issue of obesity.
Additionally, the use of smartphones as measuring tools “opens the door to new ways of doing science at a much larger scale,” Delp said.
