More than one billion adults are overweight worldwide, and more than 300 million of them clinically obese, raising the risk of many serious diseases. Only 3.6 percent of Japanese have a body mass index (BMI) over 30, which is the international standard for obesity, whereas 32.0 percent of Americans do. A total of 66.5 percent of Americans have a BMI over 25, making them overweight, but only 24.7 percent of Japanese. This paper examines the reasons Japan has one of the lowest rates of obesity in the world and the United States one of the highest, giving particular attention to underlying economic factors that might be influenced by policy changes. The average person in Japan consumes over 200 fewer calories per day than the average American. Food prices are substantially higher in Japan, but the traditional Japanese dietary habits, although changing, are also healthier. The Japanese are also far more physically active than Americans, but not because they do more planned physical exercise. They walk more as part of their daily lives. They walk more because the cost of driving an automobile is far higher in Japan, whereas public transportation is typically very convenient, but normally requires more walking than the use of a car. In terms of policy solutions, economic incentives could be structured to encourage Americans to drive less and use public transportation more, which would typically also mean walking more.