An 8 lb. infant consumes about 3 oz. of milk every 3 hr., for a total of 24 oz. per day, about 500 calories, and gains about 1 oz. per day. (These figures are rough averages; there is a lot of variation among babies.) If we scale these figures by a factor of 20 for a 160 lb. adult, we find that you would have to drink about 2 quarts of milk every three hours for a total of 4 gallons per day, about 10,000 calories, and gain a bit more than a pound per day.
Some of this has to do with size. An 8 lb. adult cat needs about 250 calories per day. The extra 250 calories that the infant eats go straight into growing. 250 calories is just the energy in 1 oz. of fat that the baby might put on in a day.
Milk is, of course, mostly water, and Judy is drinking a bit more than a gallon of water a day to be able to provide for twins.