Western Fast Foods Invading Japan : Nutrition: Working mothers are increasingly relying on ready-made meals to feed their children.

TOKYO —  While the West is showing an increasing interest in low-calorie Japanese cuisine, Tokyo teen-agers are watching their waistlines expand. On top of the list of culprits is that inevitable consequence of prosperity--fast food.

The latest Health Ministry survey shows that 10% of boys and almost 9% of girls in their late teens are overweight, about double the levels of the early 1970s.

Many Japanese teen-agers and their parents lack the time or patience to cook a traditional meal of rice, fish and bean curd, items attracting increasing attention on Western menus. “School kids’ favorites now are spaghetti, hamburgers, curry rice and potato chips,” says Emiko Hisatsune, a Tokyo school nutritionist.

Fast-food outlets and ready-made meals have become common in Japan and working mothers are increasingly relying on these meals for their children. An average urban Japanese household spends about 60% of its overall food budget on processed food, a big jump from 40% in the 1950s, according to government figures.

Doctors said an increasing number of children fall into the most serious category of weight problem, called morbid obesity. “A decade ago, these morbid obesity cases were very rare in Japan, but the number is now constantly increasing,” says Dr. Makoto Ohno, one of Japan’s leading diet specialists at the Jikei University School of Medicine. “These kids have signs of diabetes or heart disease.”

Government figures show that the average calorie consumption by a Japanese adult stands at 2,088 calories a day, far below the average for most Western countries.

“I’m sure that the younger generation takes far more than that,” says Ohno. “The discrepancy in the eating habits between the younger and the older generations here is bigger than that of any other country in the world. It is just as if the two groups came from different cultures.”

Dr. Kunizo Kataoka, a diabetes specialist at Keio University, says that the Health Ministry does not keep detailed statistics on calorie intake by age group because it does not realize that the changing eating habits of Japanese youth are a problem.

“The ministry does not even regard obesity as a disease,” he says.

Stress-related eating habits among teen-agers, particularly anorexia and bulimia, are also beginning to attract medical attention. Anorexia has long been dismissed in Japan as vain efforts to stay slim. Lack of outdoor playing space in crowded cities and Japan’s test-oriented education system are among key stress factors affecting schoolchildren and teen-agers, experts said.

“Japan is becoming a very uncomfortable place to live for kids,” said Dr. Yutaka Suzuki, a specialist in anorexia and bulimia at the Saitama Chuo Hospital. “Eating disorders stem from uncomfortable environments.” Eating disorder cases were found only in the cities, he says: “Lack of playgrounds in the neighborhood, loneliness at school, no conversation at home--these are the reasons for eating disorders.”