The Acidity of Food

There was a widely held belief that eating certain foods that were acidic would lead to stomach ulcers. Indeed for many years doctors would advise patients that were diagnosed with ulcers to avoid certain foods. People who suffer from heartburn also often try to find something in their diet that is adding acid to their stomach. But a closer look at the acidity of foods and the events that go on in the stomach during a meal shows that foods are not the source of many upset stomachs. Acidity is measured on a scale from 1 to 14 and is expressed as a pH value. A pH of 1 is very acidic, a pH of 14 is very weakly acidic or more commonly referred to as being very basic. A food or drink that has a pH of 7 is neutral, neither acidic nor basic. Distilled water has a pH of 7. Foods or drinks that have a pH below 7 are acidic, and those above pH 7 are basic. On the acidic side of the scale, a lower number means more acidic. A pH of 2 is more acidic than a pH of 3. On the basic side, a higher number means more basic. A pH of 10 is more basic than a pH of 9.

The 1-14 pH scale is not a linear scale however, which makes it a bit more complicated to understand. The pH scale is in fact a logarithmic scale. So a food that has a pH of 2 is 1 unit of pH different than a food with a pH of 3, but in fact is 10 times more acidic. If two foods have pH’s that are 2 pH units apart, their acidity is 100 times different.

Just about all foods that we eat are acidic - have a pH between 2 and 7. But the stomach is also a very acid place. Once we start eating, acid is secreted into the stomach to start the digestion process. The secretions mix with the food in the stomach and the resulting mixture can have a pH of 1.0-3.0 - very acidic. So when you eat carrots that have a pH of 6, they end up in the stomach that can be 10,000 times more acidic. Even acidic foods such as oranges, lemons or wines are not as acidic as the as normal stomach contents.

It is often not the food we eat that causes acidity problems in the stomach, but an over production of acid that is secreted into the stomach following a meal. Some foods can in fact help reduce the acidity in the stomach by neutralizing (reducing) some of the acidity. Foods higher on the pH scale will tend to do this. The beneficial effects of milk probably has more to do with reducing the acidity in the stomach contents than its reported coating of stomach lining effects.

Table 1: pH of Some Common Foods
pH of Some Common Foods
eggs 7.6 - 8.0Bananas 4.5 - 4.7
Corn 6.0 - 6.5Carrots 4.9 - 5.3
Oysters 6.1 - 6.6Cherries 3.2 - 4.0
Cow’s milk 6.3 - 6.6Oranges 3.0 - 4.0
Wheat flour 5.5 - 6.5Soft drinks 2.0 - 4.0
Potatoes 5.6 - 6.0Wines 2.8 - 3.8
Squash 5.0 - 5.4Lemons 2.2 - 2.4

Other articles on acids and bases §

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