[3] Haddon promoted a low-fat vegetarian diet and attributed all disease to unhealthy foods.

[5] Haddon stated that one could go without water if a strict vegetarian diet was adhered to as plenty of fluid could be obtained in fruits and other foods.

Haddon read a paper, "Experiments in dietetics" which argued that vegetarianism could cure alcoholism.

[9] In 1900, Haddon attended a branch meeting for The British Medical Journal at Newtown St Boswells.

Haddon argued from personal experience that a vegetarian diet improved digestion, ability to sleep, increased vigour, increased bodily temperature, improved the nervous system and gave a higher moral tone by giving up animal foods.

Haddon argued that the practice of medicine was not reaching its full potential because it was not giving dietetics a key priority.

"[11] In 1911, Haddon authored a book entitled A Doctor's Discovery, which recommended fasting and a vegetarian diet.

[12] Alexander Haig who was a friend of Haddon disputed his "one meal a day" treatment for neurasthenia and other disorders.

Haig commented that "this treatment entails underfeeding and leads eventually to defective nutrition of all the muscles, including that of the heart".

[14] At age 73, Haddon commented in the British Medical Journal, "I am going to try to be a fruitarian, for I believe that man is a frugivorous animal, as our comparative anatomists have all along taught.