PW, Dave Draper talks about this in his book "Brother Iron, Sister Steel" and on his online column as the "Tuna and Water Diet." He claims that it was common among BBers in the 1960s. He recommends it for short periods, like 3 days. I ate nothing but tuna (with seasoning) for 3 straight days, with lots of water. Recommendation - if you do this, add metamucil.