In Japan, dieting moms, smaller babies

As soon as Keiko Ozaki found out she was pregnant with her second baby, she went on a diet.


Ozaki, who teaches jazz dancing in Osaka, Japan, and weighed 112 pounds, said she was chastised by her doctor for gaining weight too quickly during her first pregnancy. With her second baby, Ozaki, 30, avoided rice and skipped meals before her monthly checkups, adding 18 pounds over nine months – 10 pounds less than U.S. women gain on average.


While Ozaki said she avoided the rebukes, her baby boy was lighter than the national average of 6 pounds, 10 ounces.


As Japan’s birth weights fall for a third decade, scientists say advice pregnant women receive may be contributing to the highest rate of low-birth-weight babies in the developed world.


More critically, it may be setting their infants up for diabetes and heart disease in later life.


“What’s happening in Japan is a shocking phenomenon,” said Hideoki Fukuoka, who studies evolutionary biology at Waseda University in Tokyo. “You hear of doctors yelling at expectant mothers and telling them to transfer to another hospital if they can’t manage their weight.”


The country’s society of obstetricians plans to follow the U.S. and U.K. in publishing guidance on weight management in pregnancy in April. The Institute of Medicine’s guidelines were released in May 2009, and the National Institute for Health and Clinical Excellence in London issued its latest advice last July.


Unlike most developed nations, where new moms are getting heavier, in Japan they’re becoming thinner. The result is that the average weight of a newborn in Japan is 7 ounces less than in 1980. The prevalence of babies weighing less than 2.5 kilos (5 pounds, 8 ounces) – low birth weight by World Health Organization standards – is now 9.6 percent, up from 5.2 percent three decades ago.


A baby’s low weight at birth is either the result of preterm delivery or restricted growth inside the womb, according to the WHO. Birth weight is affected by the mother’s own fetal growth and her diet from birth to pregnancy, and her body composition at conception, the Geneva-based agency says.


Newborns weighing less than 2.5 kilos are at greater risk of dying and suffering poor health and disability, WHO says. A growing body of scientific evidence also shows that growth-restricted infants are at increased risk of coronary heart disease, high blood pressure, stroke, Type 2 diabetes and obesity as adults.


“The nine months during pregnancy and the first two years of life will set the foundation for good health for the entire life course,” Margaret Chan, the WHO’s director general, said in a telephone interview last week.