Diabetes isn't just because of sedentary lifestyles. The evidence suggests that adult diseases are largely related to conditions found very early in life, a body of thought known as epigenetics.
For example, when mothers work into their third trimester, their children are liable to be born underweight, putting them at a unique risk of diabetes—because children who are born smallest then gain the most weight and become more vulnerable than any other group, including children born fatter.