Economic growth and diet

...at that time [eighteenth and early nineteenth centuries] food constituted between 50 and 75 percent of the expenditures of laboring families...however...the energy value of the typical diet in France at the start of the eighteenth century was as low as that of Rwanda in 1965, the most malnourished nation for that year in the tables of the World Bank. England's supply of food per capita exceeded that of France by several hundred calories but was still exceedingly low by current standards. Indeed, as late as 1850, the English availability of calories hardly matched the current Indian level.

Not surprisingly, meat was not a major source of calories in earlier times.

One implication of these low-level diets needs to be stressed: Even prime-age males had only a meager amount of energy available for work.

And get this:

...the average efficiency of the human engine in Britain increased by about 53 percent between 1790 and 1980. The combined effect of the increase in dietary energy available for work, and of the increased human efficiency in transforming dietary energy into work output, appears to account for about 50 percent of the British economic growth since 1790.

Keep all that in mind next time you despair about the modern world. The data and quotation are from Robert Fogel's The Escape from Hunger and Premature Death.