The alkaline diet is born from the premise that what we eat can change our pH. For this, we would have to eat more foods with more alkaline potential (fruit and vegetables) and less food with a more acidifying potential (red meats, dairy products, eggs and cereals), regardless of the intrinsic pH of the food. As an example, citrus fruits and cola drinks are acidic foods but do not “acidify”. Supposedly, osteoporosis, cardiovascular disease and especially cancer would greatly benefit from an eating pattern of this kind (who has not heard the nonsense that “cancer can not develop in an alkaline environment”).
Modifying the body’s pH with diet is myth
Since the pH of our body is strictly regulated because our enzymes only work in a very short interval of this same pH, it is impossible to modify it with these changes in diet . And it’s not just mouth-to-mouth based on physiology manuals, it’s been really tested , and the maximum you’ve achieved is an increase of 0.014 units of pH in your blood (which really matters), and 1.02 units of pH in the urine. Another argument was that in fact it was not possible to change the blood pH, but that it was maintained using calcium salts mobilized from our bone mass and that an alkaline diet would contribute to an improvement in bone health, something that once again is disproved  when analyzing the various studies on the subject.
Is it true that the alkaline diet can help in the prevention of cancer?
Another of the key points of this diet is the use of alkaline waters with the same intention of the previous recommendations, that is, from the prevention of cancer to an anti-aging effect . In the case of alkaline waters and cancer there are a number of interesting considerations to weave in the first place. As we have already seen, it is not the intrinsic pH of food that modifies our endogenous pH, but the composition in minerals such as chlorine, phosphates and sulfates (acids) and sodium, potassium, calcium and magnesium (alkaline). As such, alkaline waters at most could have a local effect on the stomach , increasing the pH of the medium, and potentially be useful for patients with ulcers and gastroesophageal reflux.
On the other hand, if this increase in gastric pH were confirmed, this could also have a negative effect on vitamin B12 absorption, since this acidity is fundamental in this process (hence older people with greater difficulty in producing gastric juice and individuals with taking of antacids are in the risk groups  for the vitamin deficiency). Still, none of these two potential effects with the use of alkaline waters has been properly studied and we are merely talking about hypotheses.
Moving from this local effect to a more systemic one, it is no novelty that there is no evidence  that alkaline waters can be more beneficial than conventional watersfor whatever it is, since they do not have the slightest capacity to alkalize our organism. There may still be an exception here which has nothing to do with the pH of the water, but rather with the amount of bicarbonate ingested. Some studies  found that ingestion of water supplying 2 to 3 g of bicarbonate per day had a positive effect on some markers of bone resorption, which is to say that they could make a small contribution to the improvement of our density bone mineral. The only “detail” is that the alkaline waters in the market have 120 mg of bicarbonate per liter which would make it necessary to drink 17 liters of water per day. As such, the true alkaline water is one to which one teaspoon of bicarbonate is added.
As for the relationship between acidity / alkalinity and cancer, what little can be added is the lactic fermentation of tumor cells that cause acidification of the medium (Warburg effect). It is not the acid environment that causes it, it is only a consequence of it. In this context, an alkalizing agent such as bicarbonate may have some effect on the inhibition of spontaneous metastases  and increased response to immunotherapy . Once again it is emphasized that these are small evidences in animals and with the administration of bicarbonate and not of the alkaline waters that we commonly know.
Does alkaline water bring health benefits or not?
Malicious effects on their consumption do not exist, unless it is clear that there is an excessive belief in this and other alternative therapies that lead to the abandonment of conventional treatments. As today, saving life in discussion in consultation or in social networks is precious, it is best not to try to convince anyone to change their minds. As alkaline water does not cause any harm to health, if this is a reason for the person to drink more water, nothing to oppose . The most that can happen to you is that you are a victim of satiric looks from those who really understand physiology and metabolism and know that adherence to that fashion makes no sense at all.
With the other vertices of the alkaline diet the same happens. Although the rational science does not make sense, what matters is to analyze the final output and if this approach makes someone consume more fruit and vegetables, the goal is achieved. The fruit is the same, but sold differently.
Conclusions on the alkaline diet
The world of diets on social networks today is like this. On the one hand you can not eat too much fruit because of the harmful pseudo-effects of fructose, on the other hand we have to eat it if we want to fit into the alkaline diet. On the one hand we have to eat red meat and bacon to be “paleo”, but if we want to be “paleo” we can no longer make the alkaline diet because red meat acidifies and causes cancer. But like all approaches, we can (and should) withdraw what the best they can give us, in this case is the following: