Smith was criticized by nutritionists for promoting the dangerous belief that large megavitamin dosages would help cure any disease or disorder.

[1][2] Smith was also among the first to caution against sugar, white flour, and junk food known to contribute to sickness, hyperactivity, obesity, allergies, and many illnesses in children and adults.

Smith was also a fixture on television, which is where he would receive the nickname "The Children's Doctor", which was also the title of his 5-minute ABC daytime show that ran from 1967 to 1969.

In 1993, Smith was featured in a marketing video "Homeopathic Care of Infants and Children", that promoted him as a physician, even though he was not licensed to practice as one.

[5] In the video Smith promoted dubious homeopathic remedies for chicken pox, colds, constipation, coughs, diarrhea, earaches, flu, headaches, measles and sore throats.

[2] Stephen Barrett of Quackwatch has noted that Smith advocated for pregnant women, "daily supplements of 20,000 to 30,000 units of vitamin A, a dosage high enough to cause birth defects.

According to Butler: Besides encouraging people to poison themselves and their kids with toxic doses of supplements, he recommends raw milk, avoiding foods you are allergic to because they cause obesity, diagnosis by hair analysis and cytotoxic testing, taking thyroxin pills, taking glandulars, fasting to the point of feeling weak and sick, and lots of other nonsense.

[6]In his book Dr. Lendon Smith's Low-Stress Diet, he recommended his readers to practice fasting and take only distilled water and supplements for several days to cleanse the liver.