This graph shows obesity statistics by country. (please see the link for details)
You will see the rate is extremely low in Japan (and Korea too).
I believe it is because of what Japanese have been eating. Rice/grain, vegetable, seafood and not much oil/meat.
When it comes to combating obesity, I imagine it will be very tough to try to change eating habits after so many years. I think it is natural for anybody tempted to going back to what she/he's grown up eating. I don't eat much junk food and I am eating less and less meat, but I don't think it's because I am a super-conscious eater. It's more because I didn't grow up eating junk food and a lot of meat. My body is not designed to allow too much intake of those.
So, my assumption for eating is babies/kids' eating habits is extremely important because it virtually determines what you will be in the future. Plus, it's very difficult to retrofit even if something went wrong.
Unfortunately, Japanese young people are eating more and more junk food, and obesity rate is increasing. In reaction, people started to discuss "Shokuiku". It is often translated to "food education" and what it really means is raising awareness of/re-examining eating habit. It is based on the philosophy of "you are what you eat". By carefully choosing what you eat and actively engaged in cooking, the kids will know more how to live health, both physically and mentally.
There were not much materials available in English about Shokuiku. Here is the one. It is directly linked to a pdf file, so the link will prompt you to download it.
What is Shokuiku?