Although it's not a country that is known for its overweight people, Japan has undertaken one of the most ambitious campaigns ever by a nation to slim down its citizenry. Under a national law that came into effect two months ago, companies and local governments must now measure the waistlines of Japanese people between the ages of 40 and 74 as part of their annual checkups. That represents more than 56 million waistlines, or about 44 percent of the entire population.