Ecological study of mean birth weight and nutritional intake in Japan.

The purpose of the present study was to assess the influence of nutrition on the nationwide decreases and regional differences in mean birth weight (MBW) recently observed in Japan. The relationship between MBW and nutritional intake was examined using nationwide data covering a two-decade time span from 1969 to 1988. The results of different statistical analyses indicate the MBW decreased uniformly in all 12 major regions of Japan over those 20 years (p < 0.0001). This trend was accompanied by decreases in energy and carbohydrate intake and increases in the intake of fat. We also found that the relationship between MBW and the nutrients is not linear but quadratic, showing declines in MBW only beginning from certain critical points. Hence we conclude that changes in MBW in Japan reflect the nutritional status of the Japanese, namely, decreases in the intake of energy and carbohydrate and an increase in fat intake in recent years. We also conclude that regional differences in MBW are concordant with differences in nutritional intake.