Ask a Scientist: Can balancing body chemistry help you lose weight?

Elisabetta Politi is a registered dietician and nutrition director at the Duke Diet and Fitness Center, in Durham. Here she describes the rationale behind diets based on balancing your body’s pH and whether they are likely to help you get ready for bathing suit season. Questions and answers have been edited.

Q. Diet systems like Isagenix that promise to help people lose weight by putting their body in an “alkaline state” are very trendy right now. What is an alkaline state?

A. You might remember the pH scale from high school chemistry. Essentially, the pH refers to the number of hydrogen ions in a solution – more hydrogens make it more acidic, less hydrogens make it more basic or alkaline. Readings on the pH scale below 7.0 are acidic; those 7.0 and above are alkaline. In its natural state, human blood is slightly alkaline, with a pH ranging from 7.35 to 7:45.

Q. These diets often refer to “acid ash” or “alkaline ash” – what do those terms mean?

A. Ash refers to any inorganic material, such as minerals, present in food. It's called ash because it is the residue that remains after heating removes water and organic material such as fat, protein and carbohydrates. The ash material in animal products and grains is acidic, while the ash in fruits and vegetables is alkaline. “Acid ash” and “alkaline ash” diets are based on the belief that you can change the pH of your blood, and that will yield certain health benefits.

Q. How does the pH of our bodily fluids, such as our urine and blood, affect our health and propensity to develop disease? What (if anything) does it have to do with diet and metabolism?

A. It has been suggested by lay literature and many online sites that an alkaline diet may improve the ratio between sodium and potassium ions in the body, which could benefit bone health, reduce muscle wasting and mitigate other diseases like hypertension and strokes. To my knowledge, there are no studies suggesting that an alkaline diet affects metabolism.

Q. How do our bodies become more acidic or more alkaline?

A. Our body pH varies considerably from one area to another. For example, the stomach is acidic to aid digestion and protect against harmful microorganisms. Blood pH is tightly controlled at about 7.4. The human body has an amazing ability to maintain a steady pH in the blood, mainly through the work of our kidneys and lungs. The food you eat can change the pH of your urine, but not the pH of your blood. Changing your blood’s pH would actually be quite harmful to your organs. Eating fruits and vegetables could make the urine more alkaline, whereas eating grains and meats could make it more acidic.

Q. Is there any scientific evidence to support the use of alkaline diets? If people lose weight on such diets, what is the likely cause, if not changing internal pH?

A. The alkaline diet, with its emphasis on fruits and vegetables and limits on the grains and meats that are the main sources of calories in the typical American diet might have some value in reducing obesity and chronic disease. However, the health benefits of these diets reside in cutting down calories and eating healthier foods, not in changing the internal blood pH.

This story was originally published May 23, 2015 at 11:43 PM with the headline "Ask a Scientist: Can balancing body chemistry help you lose weight?."