After McFarlane's work in the 1970s on "The Origins of English Indvidualism", some further work has come out to undermine the peasant theories that lead to misunderstandings of the Middle Ages. Work undertaken at the University of Warwick corroborates suspicions that England (and other European countries) were wealthier than realised.
"By the late Middle Ages, the English people were in a position to afford a varied diet including meat, dairy produce and ale, as well as the less highly processed grain products that comprised the bulk of the bare bones subsistence diet," he added.
Less convincing is the comparisons with modern day developing countries using per capita comparisons. Mediaeval England was not a subsistence society and did not face the sheer existential risks that modern day subsistence farmers face. In this instance, they had a better diet, but indicators such as life expectancy and infant mortality were far worse given the level of medical knowledge and the risks of dying a violent death.
Further details can be found in the work here (large pdf file).