The cost of following a special diet depends on things like the type of diet, whether the whole family is following the diet, whether you are buying ready-made meals or making them yourself.
For example, the major cost of following the gluten-free casein-free diet is buying gluten -free and/or casein -free foodstuffs, which are often more expensive than foodstuffs which contain these things. According to Stevens and Rashid (2008), gluten-free products were on average 242% more expensive than regular gluten containing products
In the UK, it is sometimes possible to obtain prescriptions for foodstuffs for patients in specific circumstances, such as when they have a confirmed diagnosis of coeliac disease but not if they have autism.
Most special diets are designed to be followed seven days a week for months or years. The amount of time you need each week will depend on the type of diet and whether you are making all of the meals yourself. In addition, it takes time to check the labels of foods you buy to ensure that they do not contain restricted foodstuffs.
For example, some proponents of the gluten-free casein-free diet recommend a trial period of three or four months. If it has not worked within that time they say it is unlikely to do so. However some researchers also suggest that the most reliable trial results are obtained after you have been on the diet for more than a year.
However, most dietitians recommend that a 2-6 week trial of an exclusion diet followed by reintroduction is adequate to identify if a dietary change has been beneficial. This is backed up by the 2011 NICE guideline food allergy in under 19s: assessment and diagnosis that recommends “if non-IgE-mediated food allergy is suspected, trial elimination of the suspected allergen (normally for between 2–6 weeks) and reintroduce after the trial. Seek advice from a dietitian with appropriate competencies, about nutritional adequacies, timings of elimination and reintroduction, and follow-up.”