Q. Should I avoid high-acid foods to stay healthy?

A. You may have heard that low-acid or "alkaline" diets help you lose weight, increase your energy, and reduce risks of heart disease and cancer. Advocates of these diets claim that eating acidic foods such as oranges and tomatoes cause health problems by altering the pH balance of our blood. Unfortunately, those dishing out this advice have no understanding of human physiology. These claims are entirely untrue.

The pH scale determines acidity by measuring the amount of hydrogen released when a substance is mixed with water. The more hydrogen, the more acidic it is. A pH of 7 is considered neutral, neither acidic nor alkaline. Acidic foods such as lemon juice and vinegar measure around 2 or 3.

Contrary to popular belief, eating acidic foods will not cause your stomach, blood or body cells to become more acidic. During digestion, the stomach becomes very acidic due to the release of hydrochloric acid. Hydrochloric acid has an extremely acidic pH of less than 1. In other words, the stomach is more acidic than the foods you eat. This acidic environment is needed for digestive enzymes to break down food properly. The acid is then neutralized after the food leaves the stomach.

The body maintains a pH range of 7.35 to 7.45. Our bodies have systems in place to keep pH in check. Whenever pH shifts outside the healthy range, the body automatically brings itself back into balance.

For example, if your blood pH starts to become acidic, your breathing rate speeds up, forcing you to blow out more carbon dioxide. This makes your blood less acidic. Neutralizing substances in the blood such as bicarbonate mop up extra hydrogen to prevent pH from becoming too acidic. Lastly, your kidneys eliminate excess acidic substances in the urine.

Deviations from the healthy range can be caused by starvation, kidney disease, or respiratory disorders.

If you have acid reflux disease, you may need to avoid acidic foods. This has nothing to do with blood pH. Acid reflux causes stomach contents to back up into the esophagus. The esophagus doesn't have the protective lining that the stomach has against acids. Acidic foods may aggravate the burning pain this condition causes.

For folks who don't have acid reflux, ignore the acid-food hype. Go eat an orange!

Amy Tousman is a registered dietitian with the Health Education Center of Straub Clinic and Hospital. Hawai'i experts in traditional medicine, naturopathic medicine and diet take turns writing the Prescriptions column. Send your questions to: Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; fax 535-8170; e-mail islandlife@honoluluadvertiser.com. This column is not intended to provide medical advice.