Black women will lose less weight than white women even if they follow the
exact same exercise and diet regimen, researchers report.
The reason behind this finding is that black women's metabolisms run more slowly,
which decreases their daily energy burn, said study author James DeLany, an
associate professor in the division of endocrinology and metabolism at the
University of Pittsburgh School of Medicine.
"African-American women have a lower energy expenditure. They're going
to have to eat fewer calories than they would if they were Caucasian, and/or
increase their physical activity more," said DeLany. His report is
published in the issue of the International Journal of Obesity.
DeLany and his colleagues reached this conclusion during a weight-loss study
involving severely obese white and black women.
Difference in results
Previous studies have shown that black women lose less weight, and the
researchers set out to verify those findings, DeLany said.
The research included 66 white and 69 black women, who were placed on the
same calorie-restricted diet of an average of 1 800 calories a day for six
months. They also were assigned the same exercise schedule.
The black women lost about 3.6 kg less, on average, than the white women,
the researchers found.
The explanation can't be that black women didn't adhere to the diet and
exercise plan, DeLany said. The researchers closely tracked the calories each
woman ate and the calories they burned through exercise, and found that black
and white women stuck to the program equally.
"We found the African-American women and the Caucasian women were both
eating nearly identical amounts of calories," DeLany said. "They were
as adherent in physical activity as well."
That leaves variations in biology and metabolism to explain the difference
in weight-loss success, the study authors said.
"The African-American women are [equally] as adherent to the behavioural
intervention," DeLany said. "It's just that the weight-loss
prescription is wrong because it's based on the assumption that the
requirements are the same."
The difference in weight-loss success between black and white women has been
known for some time, said Dr Mitch Roslin, chief of bariatric surgery at Lenox
Hill Hospital in New York City.
"There are racial and genetic differences in obesity," Roslin
said. "These things are real."
"However, this study advances our understanding by ruling out other
explanations," Roslin said. "It's not just related to socioeconomic
class or access to care or environmental situations."
One reason for the difference might be that European foods prevail in
America, and form the basis of the modern diet, Roslin said. These foods might
not burn as efficiently in the descendants of people from Africa, Asia and other
parts of the world.
"People of Western European or Eastern European descent have evolved
greater mechanisms to withstand the pressures of the modern diet," Roslin
said. He said studies have found that Asians subjected to a Western diet are
more likely to develop metabolic syndrome and diabetes at a much lower
body-mass index (BMI) than whites. BMI is a measure of body fat based on height
Weight-loss doctors will need to keep these biological differences in mind
when prescribing diet and exercise regimens for black women, DeLany said.
"They can't just base caloric restriction on body weight," he
said. "They have to take into consideration [people's] lower energy
DeLany said it's not clear whether these findings apply to black men, since
much less data is available for them. But in a diabetes intervention trial, he
said, black men lost about as much weight as white men following the same diet
and exercise plan.
For more information on weight control, visit the US
National Institutes of Health.