From Working hours: Get a life—or get fat from The Economist.
So why do long hours result in weight gain? Only 20% of American jobs are even mildly strenuous, compared to 50% in 1960. In 1960 a tenth of the American workforce was involved in agriculture, but today it's more like 1%. More time at the desk means less movement. Busy people may have less time to prepare good meals, instead choosing a take-away. (Management consultants, in my experience at least, tend to be rather knowledgeable about fancy restaurants near them that also deliver). They exercise less. And workaholics sleep less: inadequate shut-eye is associated with weight gain.50% to 20% of people with jobs that are mildly strenuous - that's a pretty big drop.