A new comparison of multi-national data, released this month, reveals that highly educated women have a healthier average weight than less educated women, but that the meaning of "healthier" changes according to a nation's relative wealth. In countries where malnutrition is prevalent, better-educated women weigh more. But in wealthier countries -- with rapidly growing rates of obesity -- better-educated women weigh less.
"As a population moves through the nutrition transition, it is the most educated, and highest income, who are the first to exit under-nutrition. They are also the first to adjust their diet and physical activity to avoid the deleterious effects of being overweight," explained John Strauss, professor of economics at the University of Southern California.
"It appears that it is women who tend to lead this transition," he added.
More than half of the adult population is underweight in Bangladesh, the poorest country analyzed by Strauss and Duncan Thomas (Duke University). In Bangladesh, average female body mass increased with every additional year of schooling.
In contrast, only 1 percent of people in the United States are underweight. Better-educated women in the United States, the wealthiest country in the study, had a lower average body mass index the more education they'd received, the researchers found.
"Obesity rates rise with economic development which is troubling given the relationship between obesity and cardiovascular disease, stroke, diabetes and possibly cancer," Strauss said. For example, the researchers show that almost twice as many women are now overweight as are underweight in China.
Furthermore, in developing countries worldwide, women are more likely than men to be overweight or obese. The gender gap is largest in South Africa, where more than one-third of women are obese, compared with about 10 percent of South African men.
However, Strauss and Thomas show that once women receive a certain amount of schooling, average body mass index (BMI) falls and they are more likely to be at a healthy weight.
"Behavioral changes have important impacts on health outcomes," Strauss said.
For example, the average BMI of a Mexican woman -- where 74 percent of the women are overweight or obese -- declines for every year of schooling she receives in excess of just five years. There is a similar sharp decline in the average female's BMI in South Africa after five years of education.
BMI is a widely used measure that accounts for both weight and height.
The United States was the only nation surveyed in which better-educated men had a lower average BMI than less-educated men. In every other country, the average male body mass increased with every additional year of schooling.
The findings appear in the latest volume of the "Handbook of Development Economics," edited by Strauss and T. Paul Schultz (Yale University). The new book is the first update in more than 13 years to the "Handbook of Development Economics," which has counted at least six Nobel Prize laureates among its contributors.
"Data has vastly improved since the last volume," said Strauss, who is also the principal investigator for the long-term Indonesia Family Life Survey, which tracks more than 30,000 individuals.
An unmatched resource for scholars, the "Handbook of Development Economics" summarizes and synthesizes important research about economic development, including the role of institutions such as schools, medical facilities and fair court systems. Nobel Prize laureate Amaryta Sen wrote the first chapter of the first volume of the "Handbook in Development Economics" in 1988.
Topics explored in the latest volume, released in April 2008, include the decline of agricultural employment, the effects of changing fertility through availability of contraception or family planning programs, child labor and political corruption.
Schultz, T.P. and John Strauss. "Handbook of Development Economics: Volume 4," (Amsterdam: North-Holland Press, 2008).