Several misconceptions exist about foods and nutrition. Many believe, that the human body can “acidify”, thus, an “alkaline diet” should be followed. The acid-base balance is a characteristic of a normally functioning human body. Throughout our metabolic processes, acids and substances with acidic pH are produced continuously, which, in the case of a healthy person, does not affect the pH of the human body. In those rare cases, when an overall pH imbalance evolves in the human body due to its life-threatening nature, it requires urgent medical intervention. Furthermore, it cannot be influenced by dietary interventions. This paper highlights evidence regarding acidification and the acid-base balance, with special attention to certain food groups. Foodstuffs have different specific pH value (acid-base character), they can be acidic, alkaline, or neutral in elemental state. Beside their chemical nature, the effect they have on the human body depends on the mechanism of their metabolism, as well. Diet and ingredients have direct and indirect effects on the human body's intracellular and extracellular compartments (especially blood and urine), still they do not influence its pH significantly. Alkaline diets were born in the absence of evidence-based information and/or the misunderstanding and wrong interpretation of the available and up-to-date scientific facts. The convictions of consumers and the promotion of the alkaline diet lack the scientific basis, so it can be harmful or even dangerous in the long run. In summary, scientific evidence on the efficacy or prophylactic effects of an alkaline diet is not available.