By Asker Jeukendrup from mysportscience.com
An alkaline diet, alkaline water, alkalising supplements are often promoted in the lay press as “healthy”. There is a whole movement that promotes an alkaline diet, claiming our current diet is to acidic. Its proponents say too much acidity in the body can lead to poor health and following an alkaline diet can prevent and cure conditions including cancer, cardiovascular disease and osteoporosis. The diet favours vegetables and fruits, along with specialty waters and supplements, over grains and animal products. This blog will analyse the evidence.
Let’s start with reminding ourselves what alkaline means. Acidity is related to the concentration of hydrogen (H+) measured as pH. A pH of 7 is neutral. Water usually has a pH of around 7. If the acidity increases, the pH decreases, and we call it acidic. If the pH increases, we call it “alkaline” or “basic”. Examples of an acid liquid is a sports drink, a soft drink or orange juice, typically with a pH of around 3. Bleach has a pH of about 12 and is very alkaline.
The theory that an alkaline diet is healthy is derived from the so called “acid ash hypothesis” that was published in 1912. Here is a link to this original paper: https://www.jbc.org/content/11/4/323.full.pdf
In this paper it is discussed that certain foods, when burned, produce a more alkaline ash and others a more acidic ash. From here the assumption was made that this would also happen in the body and thus a diet from foods that produce a more alkaline ash would result in an alkaline body, and this would be better for health, prevent and even cure disease. The alkaline or acidic characteristics of foods were linked to the mineral components of foods make the body acidic, alkaline or neutral. It was then suggested that in order to achieve a more alkaline load, one must consume more fruit and vegetables with only a moderate intake of protein. According to the alkaline ash diet, some foods that we would think of as being acidic, like citrus, are actually considered alkaline-producing.
According to the theory, certain food groups are considered acidic, alkaline, or neutral:
Acidic: meat, poultry, fish, dairy, eggs, grains, alcohol
Neutral: natural fats, starches, and sugars
Alkaline: fruits, nuts, legumes, and vegetables
Just a theory
The alkaline ash diet is just a theory and there are a number of assumptions that should be tested. Unfortunately, despite the large number of publications in the lay press, there are almost no scientific studies to test this theory and there is no limited or no evidence to support or refute the theory.
What we do know
But there are a number of things we do know. When we eat food and it travels through the digestive tract there are some very significant changes to the pH. In the mouth, food is mixed with saliva in a fairly neutral environment before it ends up in the stomach which is strongly acidic. Then the food moves into the intestine where it is neutralised with alkaline substances. This is important so it can be absorbed. The pH in blood is tightly controlled between 7.35 and 7.45, slightly alkaline. The maintenance of blood pH is critically important, deviation from this range would mean that enzymes don’t function and death would be the result and the body has various mechanisms to maintain blood pH (several buffers and excretion mechanisms, excess hydrogen ions get quickly buffered by bicarbonate for example and excreted through urine and CO2.
Followers of the diet sometimes measure the pH of a sample of their saliva or urine to work out if their body is alkaline or acidic. However, pH of urine does not tell you anything about blood pH. A well-controlled randomised trial of an acidic diet changed systemic pH by only 0.014 units. However, the pH of urine increased by 1.02 units (1) This study reveals that diet changes can alter urine pH but does not change blood pH.
In addition to this, the effect of phosphorus on calcium metabolism is opposite to that was predicted by the hypothesis (2). So, there are plenty of questions about the validity of the hypothesis and no data to support it.
The diet was popularised through Dr Young, who wrote several books on the topic. According to this theory protein and grains in the diet produce a high acid load in the body which causes a number of health issues. For example, it is supposed to release calcium from the bones, causing osteoporosis. He links it with cancer, cardiovascular disease.
What is perhaps important to know is that Dr Young, who wrote books like The pH Miracle: Balance Your Diet, Reclaim Your Health, The pH miracle for weight loss, and several other books with similar titles. The “doctor” promoted the alkaline diet to a large number of patients and claimed to have treated many patients with the miracle cure. However, it turns out, Dr Young was not even a doctor and in 2017 Robert O. Young was sentenced to prison for practicing medicine without a license (read more here: https://quackwatch.org/11Ind/young3/).
While the original theory claimed that an acid-producing diet would leach calcium from your bones, a recent meta-analysis found this wasn't the case. Craig Sale also discussed the topic in a guest blog for Mysportscience (in this case it was specific tom the role of protein in the diet).
An alkaline diet has also been hailed as a prevention or cure for cancer, but recent meta-analysis and reviews have found no evidence the acidity or alkalinity of food affects cancer risk (3). The alkaline diet emphasises, to varying degrees, fresh fruits, vegetables, roots and tubers, and legumes with only a moderate protein intake. It is possible that some of these foods may have cancer-protective effects, not through their acidity/alkaline-promoting qualities but rather due to nutrient and non-nutritive compounds.
Buying expensive specialty waters, supplements and programs to alkalise your body is unlikely to help you avoid complex health conditions. Diet is NOT going to change the pH of your blood. If it did we would be in big trouble. Don’t waste your time and money on this idea, the hypothesis, any books or special products related to this diet. Of course, keep buying fruits and vegetables.
Buclin T, Cosma M, Appenzeller M, et al. Diet acids and alkalis influence calcium retention in bone. Osteoporos Int 2001;12:493–9.
Fenton TR, Lyon AW, Eliasziw M, et al. Phosphate decreases urine calcium and increases calcium balance: a meta-analysis of the osteoporosis acid-ash diet hypothesis. Nutr J 2009;8:41.