If the plant is mostly water, is that water different because it is being filtered through the plant vs water through a reverse osmosis filter for example? If the plant is grown by the person consuming it, the water will have a higher capacity to increase the vital capital of that person. When I say it depends on the conditions in which it's grown this is what makes the difference. The lettuce itself isn't the problem it's the way it's cultivated. Food is medicine and especially so when growing it yourself.