You are right some diets work better than others for some people. However, a credible diet for managing IBS has to built on facts about the human digestive system not fiction.
Shelton and later Hay's diets are derived on old, some would say ancient, physiological notions we now know are completely inaccurate. Our bodies just don't digest foods the way these people thought they did. The basic notions of the diet are completely incorrect from a physiological and medical point of view.
Here is an example "The acids of acid foods inhibit the secretion of the digestive acids required for protein digestion. Undigested proteins putrefy in bacterial decomposition and produces some potent poisons." Acids from foods don't affect very acidity enviroment in the stomach juices hardly at all. More importantly there is no bacterial decomposition in the stomach. The stomach releases protein-digesting enzymes and hydrochloric acid into the stomach that kills or inhibits bacteria and provides a very acidic pH for the enzymes to work. Also the notion that "acids neutralize the alkaline medium required for starch digestion and the result is indigestion and fermentation" is nonsense! The stomach juices (chime) is never ever alkaline -- the ph of the stomach is always kept very acidic between ph 1 and 2. The ph in the small intestine is very acidic too with a ph between 3 and 4. The ph of the stomach would have to rise to above 7 in order to be considered alkaline in which case the person wouldn't be dead. The basic physiological principles have to be correct before a diet can make sense! Anyone who paid attention in high school health and science would know the ideas this diet is based on are inaccurate.
-------------------- STABLE: ♂, IBS-D 50+ years - Science of IBS