When you sit down to a meal, you may think about how many calories it  has... the amount of fat or carbs you're consuming...and which vitamins and minerals you're getting. You probably don't think about the meal's acid load. You should. Why? Because once they're inside you, certain foods lead to the production of a lot of acid-and that acid may increase your risk of developing diabetes, a recent study shows.

Shocker: Foods that you'd generally think of as acidic (oranges, tomatoes, lemons, etc.) are not the ones to worry about. Instead, the acid producers include some foods you probably consider healthful. Here's what to watch out for...

Acid Scoring

To understand the recent study, let's review a little chemistry. Remember that pH, ranging from zero to 14, is a measure of the acidity or alkalinity of a substance, which has to do with the concentration of hydrogen ions. A pH of 7.0 is neutral...numbers below 7.0 are more acid...numbers above 7.0 are more alkaline. The normal healthy pH range for human blood and tissues is slightly more alkaline than acid, with a pH of about 7.35 to 7.45.

Severe pH imbalances are known to be life threatening, and more moderate imbalances can compromise bone health and lead to kidney stones. Researchers decided to investigate how pH affects diabetes risk. They drew on data from more than 66,000 women who did not have diabetes at the start of the study. In 1993, these women completed questionnaires about how often and in what quantities they consumed 208 different foods. The researchers then did a nutritional analysis, calculating each woman's dietary acid load based on the potential renal acid load (PRAL) scores of the foods she ate. The PRAL score takes into account the intestinal absorption rates of protein, phosphorus, potassium, calcium and magnesium, all of which contribute to maintaining the acid-alkaline balance.  Negative PRAL scores reflect alkaline-forming potential, while positive PRAL scores reflect acid-forming potential.

Based on their PRAL scores, participants were divided into four equal-sized groups. The lowest-scoring group had the most alkaline-forming diet... the highest-scoring group had the most acid-forming diet. Then, for the next 14 years, the researchers kept track of developed diabetes-as almost 3,500 of the women did.

What the researchers found: Women with the lowest PRAL scores were the least likely to develop diabetes. Compared to that group, women with the highest scores (representing a high acid load) were 56% more likely to develop diabetes. This held even after researchers adjusted for other diabetes risk factors, such as body mass index (BMI), physical activity, smoking, high blood pressure, high cholesterol and family history of diabetes. Surprisingly, the association between a high acid load and diabetes risk was even more pronounced among women of normal weight (with a BMI of 25 or less) than among over weight women.

Which Foods are Acid-Forming?

In this study, the high-risk high-PRAL diets were characterized by higher consumption of fat and protein (mainly from animal protein-meat, poultry, fish) and also by consumption of bread and soft drinks, especially artificially sweetened drinks. In contrast, women who followed a low-risk low-PRAL diet tended to consume more fruits, vegetables, dairy products and coffee.

PRAL example: A three-ounce chicken breast without the skin has a PRAL score of 9.43...whereas an orange scores -4.24 and a cup of broccoli scores -5.6.

What might be the metabolic mechanism behind these findings? Our lungs and kidneys are responsible for maintaining a health pH by eliminating excess amounts of acid or alkaline from the body. The lungs take care of carbon dioxide and the kidneys take care of all other acids. But when the kidneys aren't able to keep up with the task, a condition called metabolic acidosis arises. According to the study researchers, a diet that creates a high acid load may contribute to chronic metabolic acidosis, which in turn leads to insulin resistance and metabolic syndrome-which are risk factors for diabetes.

Additional evidence: Animal studies have shown that metabolic acidosis decreases the ability of insulin to bind to insulin receptors...and human studies have shown that some markers of metabolic acidosis are associated with insulin resistance.

Bottom line: The study doesn't mean that you should shy away from fish, which has been shown to have cardiovascular health benefits. But it does give you one more excellent reason to make sure that your diet includes plenty of fruits and vegetables and a moderate amount of dairy.

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