Normally, in Agricola, it would be crazy not to spend food on feeding your family - at a cost of 3 VPs per, it is difficult to imagine any situation where a food token could be worth more in the future than sparing you a Begging card now.
However, here's the corner case I'm currently in. I have in my hand the Mendicant Occupation. It seems quite likely that I'll go into the first Harvest with only 3 food tokens. Is it acceptable for me to feed my Family with only 2 of the Food, taking 2 Begging cards (both of which I plan to ditch to the Mendicant later on), and saving 1 Food for the purposes of paying for a second Occupation in Round 5?
I'm pretty sure you can't be forced to convert resources into food to feed your family if you don't want to, but it seems to me that the rules are slightly less clear on whether food must be eaten if you have it. (I'm playing this game online, so it will be interesting to see if the option to not eat food is even given by the program...)