Alkaline diet (also known as the alkaline ash diet, alkaline acid diet, acid ash diet, and the acid alkaline diet) describes a group of loosely related diets based on the belief that certain foods can affect the acidity and pH of bodily fluids, including the urine or blood, and can therefore be used to treat or prevent diseases. Due to the lack of human studies supporting any benefits of this diet, it is generally not recommended by dieticians and other health professionals.[1]
The relationship between diet and acid-base homeostasis, or the regulation of the acid-base status of the body, has been studied for decades, though the medical applications of this hypothesis have largely focused on changing the acidity of urine. Traditionally, this diet has advocated for avoiding meat, poultry, cheese, and grains in order to make the urine more alkaline (higher pH), changing the environment of the urine to prevent recurrent urinary tract infections (UTIs) and kidney stones (nephrolithiasis). However, difficulties in effectively predicting the effects of this diet have led to medications, rather than diet modification, as the preferred method of changing urine pH. The "acid-ash" hypothesis has been considered a risk factor for osteoporosis by various scientific publications, though more recently, the available weight of scientific evidence does not support this hypothesis.
The term "alkaline diet" has also been used by alternative medicine practitioners, with the proposal that such diets treat or prevent cancer, heart disease, low energy levels as well as other illnesses. These claims are not supported by medical evidence and make incorrect assumptions about how alkaline diets function that are contrary to modern understanding of human physiology.
According to the traditional 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.[2]
It has been suggested that diets high in "acid ash" (acid producing) elements will cause the body to try to buffer (or counteract) any additional acid load in the body by breaking down bone, leading to weaker bones and increased risk for osteoporosis. Conversely, "alkaline ash" (alkaline producing) elements will hypothetically decrease the risk of osteoporosis. This hypothesis has been advanced in a position statement of the American Dietetic Association,[2] in a publication of the U.S. National Academy of Sciences,[3] as well as other scientific publications,[4] which have stated foods high in potassium and magnesium such as fruits and vegetables may decrease the risk of osteoporosis through increased alkaline ash production. This acceptance of the acid-ash hypothesis as a major modifiable risk factor of osteoporosis by these publications, however, was largely made without significant critical review by high quality systematic analysis.[5]
Recent systematic reviews have been published which have methodically analyzed the weight of available scientific evidence, and have found no significant evidence to support the acid-ash hypothesis in regards to prevention of osteoporosis. A meta-analysis of studies on the effect of dietary phosphate intake contradicted the expected results under the acid-ash hypothesis with respect to calcium in the urine and bone metabolism. This result suggests use of this diet to prevent calcium loss from bone is not justified.[5] Other meta-analyses which have investigated the effect of total dietary acid intake have also found no evidence that acid intake increases the risk for osteoporosis as would be expected under the acid-ash hypothesis.[4][6] A review looked at the effects of dairy product intake, which have been hypothesized to increase the acid load of the body through phosphate and protein components. This review found no significant evidence suggesting dairy product intake causes acidosis or increases risk for osteoporosis.[7]
It has also been speculated that this diet may have an effect on muscle wasting, growth hormone metabolism or back pain, though there is no conclusive evidence to confirm these hypotheses.[8][9][10] Given an aging population, the effects of an alkaline diet on public health may be worth considering, though there is little scientific evidence in this area.[10]
Alternative medicine practitioners who have promoted the alkaline diet have advocated its use in the treatment of various medical conditions including cancer.[11] These claims have been mainly promoted on websites, magazines, direct mail, and books, and have been mainly directed at a lay audience.[4] While it has been proposed that this diet can help increase energy, lose weight, and treat cancer and heart disease, there is no evidence to support any of these claims.[12] This version of the diet, in addition to avoiding meats and other proteins, also advocates avoiding processed foods, white sugar, white flour, and caffeine,[9] and can involve specific exercise and nutritional supplement regimens as well.[13]
Advocates for alternative uses of an alkaline diet 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, which can foster disease.[9][12] 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 a "myth" in a statement by the American Institute for Cancer Research.[14] Unlike the pH level in the urine, a selectively alkaline diet 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 just can, at most, change the blood pH minimally and transiently.[1][9][12][14]
A similar proposal by those advocating this diet suggests that cancer grows in an acidic environment, and that a proper alkaline diet can change the environment of the body to treat cancer. This proposal ignores the fact that while cancer tissue does grow in acidic environment, it is the cancer that creates the acidity. The rapid growth of cancer cells creates the acidic environment; the acidic environment does not create cancer.[11] The proposal also neglects to recognize that it is "virtually impossible" to create a less acidic environment in the body.[14] "Extreme" dietary plans such as this diet have more risks than benefits for patients with cancer.[11]
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Alkaline diet - Wikipedia, the free encyclopedia
