Popular in its day, the diet has since been referred to as an "outmoded treatment"; there is no good evidence that it is effective, and it is difficult for people to follow.
The diet was originally based on the elimination of salicylate, artificial food coloring, and artificial flavors; later on in the 1970s, the preservatives BHA, BHT, and (somewhat later) TBHQwere eliminated. Besides foods with the eliminated additives, aspirin- or additive-containing drugs and toiletries were to be avoided.
Even today, parents are advised to limit their purchases of mouthwash, toothpaste, cough drops, perfume, and various other nonfood products to those published in the Feingold Association's annual Foodlist and Shopping Guide.
Some versions of the diet prohibit only artificial food coloring and additives. According to the Royal College of Psychiatrists as of 2014 the diet prohibited a number of foods which contain salicylic acid including apples, cucumbers and tomatoes.
Feingold stressed that the diet must be followed strictly and for an entire lifetime, and that whole families – not just the subject being "treated" – must observe the diet's rules
Further information: Diet and attention deficit hyperactivity disorder
Although the diet had a certain popular appeal, a 1983 meta-analysis found research on it to be of poor quality, and that overall there was no good evidence that it was effective in fulfilling its claims.
In common with other elimination diets, the Feingold diet can be expensive and boring, and so difficult for people to maintain.
In general, as of 2013 there is no evidence to support broad claims that food coloring causes food intolerance and ADHD-like behavior in children.
It is possible that certain food coloring may act as a trigger in those who are genetically predisposed, but the evidence is weak.