According to a study of 1,700 Vermont teenagers, published in the journal Pediatrics, 29 percent were overweight or obese. However, "As for walking or biking to school, Drake and his colleagues found those who commuted more than three days per week were least likely to be obese." In terms of numbers, "Those who walked or biked to school four to five times per week were 33 percent less likely to have weight problems." (You can find an abstract at this LINK and a July 16 news report at this LINK).
This is credible evidence that our prevailing development patterns--subdivisions on highways which make walking and biking to school unsafe and undesirable--are contributing significantly to what the American Academy of Pediatrics terms an "epidemic" of childhood obesity.