One thing that you learn pretty quickly in Japan is that it's not so much about what you eat but how much of it you eat. People would be surprised to see just how much food which people in western countries consider verboten as part of a healthy diet is commonly consumed in Japan (particularly high fat food). The Japanese are expert at packaging for small portions in order to accomodate small appetites. The package above is 100 grams of rice that you can buy in a package that snaps apart so you can conveniently eat a tiny portion. It's actually one of my favorite buys as it's about right for me when I eat rice.
There are a wide variety of these types of portion-controlling packages in Japan. For instance, you can buy a Kit Kat bar in 8 individually-wrapped pieces which are half the size of one wafer. Imagine taking a regular Kit Kat with 4 bars that snap apart and cutting them all in half and individually wrapping them. Even a regular bar doesn't come packaged as one block of 4 bars. It comes as 2 bars of 2 wafers individually-wrapped. The exception to the small portions in Japan is giant bars (mainly geared toward kids as gifts) which are offered around New Year's. Roy has a picture of one of these big bars in his blog Q-Taro in the archives here. I believe there are also Giant Pocky on offer during this time of year as O-shogatsu (New Year's) gifts.
This picture pinched from Amazon (from which you can buy these in the States).
Beyond the individually-wrapped items, there is the the fact that all food is sold in smaller packages period. A "bag of chips" in Japan is around 70-100 grams (about 3.5-4.5 ounces). In the U.S., an average bag of potato chips (unless it is an individual portion meant to be put in a lunch pail) is 9-12 ounces.
In the U.S., you find that food companies for many years had been offering more and more in each package whereas Japan almost always offers less with a few exceptions. Studies show that people eat more if more is in front of them. This is probably a leftover survival behavior. If you eat all you can when it's there, you store fat and have a greater chance of living through leaner times.
Since food is cheap in the U.S. (the packaging sometimes costs more than the contents), companies have emphasized size as value and people have tended to choose more content for their money rather than less. This has pushed all food and snack companies to make bigger and bigger portions in order to make people feel they are getting value for their money.
It also doesn't help the restaurants have been on the same portion-bloating bandwagon for years. I read recently in an interview on Salon that dinner plate sizes now are similar to serving platter sizes from 80-100 years ago. Dinner plates used to be the size of current salad plates. People in the U.S. have a tendency to feel satisfied about what they're eating when they have a full plate and a bigger plate means more food.
When you mix the marketing value of larger portions with the psychology of eating, you get people eating more and more. Only now in the U.S. is the issue of selling individually-packaged portions to give people an idea of how much they should consider a reasonable amount starting to gain momentum. In Japan, the idea seems to have always been here.
I'm not sure if the control of portion sizes in Japan is the result of a culture which serves a variety of small dishes traditionally, part of the group culture, related to a culture which doesn't view size as such an important factor in "value" or an off-shoot of a culture which values packaging so much. The small portions in separate packages do make it easy to share and in fact encourage it when you're around other people. If you're alone, you're very aware each time you tear open a new package for another cookie that you're tucking in again. You get a feeling of going beyond one portion. You also don't have to think about food going stale if you don't eat it all up because it's vacuum-sealed and will stay just fine for weeks.
So, I believe there is little danger that Krispy Kreme is going to unleash a wave of obesity in Japan. There's far too much cultural push behind moderation and small portions for any one infusion of American culture to convert Japan to a culture of excess.