How much should a person consume?

How much?

"If we are concerned about our great appetite for materials, it is plausible to seek to increase the supply, or decrease waste, to make better use of the stocks that are available, and to develop substitutes. But what of the appetite itself? Surely this is the ultimate source of the problem. If it continues its geometric course, will it not one day have to be restrained? Yet in the literature of the resource problem this is the forbidden question. Over it hangs a nearly total silence." John Kenneth Galbraith, The Affluent Society, 1958