with resulting nutrient deficiencies such as essential fatty acids and phytonutrients. Many websites and books promoting this diet sell courses of supplements and foods which are unnecessary to purchase even under the diet's own terms. The level of effort needed to use this diet is considered "high" as there are many foods that need to be excluded. Proposed mechanism According to the traditional acid ash hypothesis underlying this diet, acid ash is produced by meat, poultry, cheese, fish, eggs, and grains. Alkaline ash is produced by fruits and vegetables, except cranberries, prunes and plums. Since the acid or alkaline ash designation is based on the residue left on combustion rather than the acidity of the food, foods such as citrus fruits that are generally considered acidic are actually considered alkaline producing in this diet. Advocates propose that since the normal pH of the blood is slightly alkaline, the goal of diet should be to mirror this by eating a diet that is alkaline producing as well. These advocates propose that diets high in acid-producing elements will generally lead the body to become acidic and thereby foster disease. because it is "virtually impossible" to create a less acidic environment in the body. While a selectively alkaline diet may change the pH level in the urine, it has not been shown to elicit a sustained change in blood pH levels, nor to provide the clinical benefits claimed by its proponents. Because of the body's natural regulatory mechanisms, which do not require a special diet to work, eating an alkaline diet can, at most, change the blood pH minimally and transiently. A similar proposal by those advocating this diet suggests that cancer grows in an acidic environment, and that an alkaline diet can change the environment of the body to treat cancer. However, contrary to the premise of the proposal, it is rapid growth of cancer cells that creates acidic environment associated with cancer; the acidic environment does not create cancer. "Extreme" dietary plans such as this diet have more risks than benefits for patients with cancer. Evaluation The British Dietetic Association named the alkaline diet one of the "top 5 worst celeb diets to avoid in 2018", branding it as "nonsense". This proposed mechanism, in which the diet can significantly change the acidity of the blood, goes against "everything we know about the chemistry of the human body" and has been called