Low Birth Weight and Risk of Obesity : A Potential Problem for the Japanese People

In the last half-century, obesity has constantly increased in Japanese adults except for women of childbearing age who often desire to be thin. Considering the lean composition of Japanese mothers and rather strict restrictions on maternal weight gain during pregnancy in Japan, there is concern that increasing numbers of young Japanese have been undernourished during the pre-conceptional as well as conceptional period. Indeed, increasing numbers of neonates have been born with low birth weights in Japan. Animal studies suggest that a combination of undernourishment in utero and normal or high levels of nutrients in the neonatal period plays a critical role in connecting a low birth weight with obesity in later life, leading to the concept of a ‘thrifty phenotype’ proceeding to ‘mismatch’ to high levels of nutrients after birth as a risk of obesity. Results obtained with rodent models have suggested that hypothalamic plasticity in the early developmental period plays a critical role in the mechanistic framework.