In the context of sustainable development, we investigate four subsistence communities, one each from India, Bolivia, Laos and Thailand, to understand the systemic interrelations between the food production systems and related environmental pressures. In doing so, we revisit Ester Boserup's theory of increasing land productivity at the expense of declining labour productivity as a consequence of agricultural intensification. Our data confirm Boserup's assumptions within the reach of traditional agriculture, but find them not to apply to hunting & gathering communities and to agricultural systems now increasingly dependent on fossil fuels and industrial fertilizers. Instead we propose a theory of 'sociometabolic transitions' as being more appropriate to understanding transitions in land and labour productivity across a wider range of modes of subsistence.