The rise in obesity has largely been attributed to an increase in calories intake and a reduction in physical exercise. This paper analyses how these two effects can be explained by structural change, i.e. the shift from manufacturing to services. First, service occupations are on average less strenuous, thus leading to lower exercise. Second, the rise in services increases households labour market participation and the opportunity cost of cooking at home, thus rising the demand for restaurant and fast-food meals, typically higher in calories. We rationalise these two mechanisms with an estimated multi-sector structural transformation model of the US economy with home and market food production.