This section is from the book "The Hygienic System: Fasting And Sun Bathing", by Herbert M. Shelton. Also available from Amazon: The Hygienic System Vol III Fasting and Sun Bathing.
One of the most frequent dietetic errors is that of mistaking appetite for hunger. Appetite is no more hunger than sexual passion is love. Graham made a sharp distinction between an "appetite" which is merely the expression of habit (the habit of eating at certain times) and "that natural and healthy hunger which is a physiological manifestation of the real alimentary wants of the body" and asserted that it "is of the utmost importance that this distinction should ever be kept in view," when considering man's dietary habits. Appetite, which is so much a matter of habit, has sometimes been referred to as "habit-hunger," but I do not think the inclusion of the word hunger in this compound term is correct. As has been previously pointed out, habit may be morbid, true hunger never is. Bulimia, or an ox-like appetite, is seen in a number of states of disease, but it has no more relation to true hunger than a headache has to the appreciation of music.
Horace Fletcher says that the "mark of distinction" that differentiates real hunger from appetite is the "watering of the mouth for some particular thing." Appetite is indiscriminate and often finicky. "Natural hunger is never in a hurry," declares Carrington. Appetite is often in a big hurry.
Pavlov showed that appetite for food, which cannot be hunger, may be induced by swallowing a mouthful of wine. He says that at the moment the wine reached the stomach, he "perceived the onset of a very strong appetite." What he mistook for a demand for food was irritation of the stomach. He made the same mistake here that Cannon made in mistaking similar irritation for hunger.