Vinegar is an acid with ph value less than 7, but as a food, it is alkaline. Acid and acidic food are two different concepts. The scientific name of acetic acid is acetic acid. Before it is absorbed and metabolized by the body, it is uncompromisingly acidic. Generally speaking, all sour substances are acidic. Once acetic acid stepped from the chemical field into the field of food nutrition, acetic acid became an alkaline food. The acidity or alkalinity of acidic or alkaline food is not necessarily related to the acidity or alkalinity of the substance before it enters the human body. To determine the acidity or alkalinity of food, it mainly depends on the alkaline elements contained in food, the result of metabolism of acidic elements and organic acids in the human body. The usual simple method of determination is that any food containing high chlorine, sulfur, phosphorus and other non-metallic elements is mostly acidic food because its final metabolites are acidic after being ingested into the human body. Foods containing more metal elements such as calcium, potassium, sodium and magnesium are mostly alkaline foods because their final metabolites are alkaline after being ingested. Acetic acid entering the body undergoes a series of biochemical reactions and finally produces carbon dioxide and water, which is eliminated by the lungs, thus reducing the carbonic acid content of the blood and making the body fluid weakly alkaline. Acetic acid is an alkaline food.