Western Vs. Eastern pregnancies

Okay, so I have to ask and go ahead and get your opinions.  So Half of my family is Japanese and they have been delivering babies in Japan healthy and bouncing back in weight within months of being pregnant.  I have noticed that what their doctors deem acceptable does not a line with what is said here in the US.   Like always eastern vs western medicine.  But in the end things like green tea, seafood, amount of weight to gain and just overall lifestyle changes that are deemed necessary by the two different groups.  I guess I'm perplexed on how the two locals can cause such a deviation in pregnancy advice.