Saturday, November 23, 2013

High Dietary Acid Load May Raise Risk For Type 2 Diabetes

Fruits and vegetables, such as the winter squashes shown,
can help reduce dietary acid load.
A large prospective study found that the higher a woman's dietary acid load, the greater her risk for type 2 diabetes:

Dietary Acid Load And Risk Of Type 2 Diabetes: The E3N-EPIC Cohort Study, Diabetologia, Published online 11 November 2013

Researchers from France followed 66,485 women teachers for 14 years. The women were part of the E3N-EPIC cohort. They were sectioned into 4 groups or quartiles, corresponding to the acid load of their diet. Those in the highest quartile, consuming foods with the most acid-forming potential, had a 56% increased risk of developing type 2 diabetes compared to those in the lowest quartile.

Interestingly, women with normal body weight (BMI less than 25) had the highest risk - a 96% increased risk for developing type 2 diabetes (top quartile compared to bottom). Overweight women (BMI 25 and over) had a 28% increased risk. However, this could indicate that the association between an acid-forming diet and diabetes is independant of body weight.

Given the long follow-up, researchers were able to rule out reverse causation, that is, the possibility that diabetes led to acidosis.

The researchers concluded:
"We have demonstrated for the first time in a large prospective study that dietary acid load was positively associated with type 2 diabetes risk, independently of other known risk factors for diabetes. Our results need to be validated in other populations, and may lead to promotion of diets with a low acid load for the prevention of diabetes. Further research is required on the underlying mechanisms."

Is Insulin Resistance The Mechanism?

Cross-sectional studies have shown that a high dietary acid load is associated with insulin resistance. Acidosis may interfere with binding of insulin to its receptors, or may result in decreased insulin secretion:
"The induction of mild acidosis by the administration of ammonium chloride results, in humans, in reduced insulin sensitivity, as assessed by the gold standard technique, the euglycaemic clamp. Furthermore, metabilic acidosis decreases the binding of insulin to its receptors in rats, suggesting that metabolic acidosis may promore insulin resistance. Finally, in experimental studies, acid/base alterations are associated with decreased insulin secretion."
"Type 2 diabetes incidence and glucose intolerance have been shown to be higher in people with a lower urinary pH [more acidic] than in those with a higher urinary pH."

What Is An Acid-Forming Diet?

An acid-forming diet has the potential to drive body fluids to a lower, or more acidic pH. (The body works to maintain blood in a tight, slightly alkaline pH range of 7.35 to 7.45.)

In this study, two equations were used to estimate the acid-forming potential of a diet:

Potential Renal Acid Load (PRAL):
PRAL = 0.49 Protein (g/d)* + 0.037 Phosphorus (mg/d) - 0.021 Potassium (mg/d) - 0.026 Magnesium (mg/d) - 0.013 Calcium (mg/d)

Net Endogenous Acid Production (NEAP):
NEAP = 54.5 Protein (g/d) / Potassium [mEq/d) − 10.2

* Protein is used as an estimate for sulfate.1 Protein is made up of amino acids. Of the 20 common protein-sourced amino acids in food, only 2 contain sulfur: methionine and cysteine.

Of note in these equations, foods high in protein (especially proteins high in methionine and cysteine) and to a lesser degree phosphorus have a high acid-forming potential. Foods high in potassium and magnesium have a low acid-forming potential. (Remer et al. found that eliminating calcium from the equation improved prediction of acid effect.1)

You can estimate the acid-forming potential of a food by substituting actual values into the equations. A database such as NutritionData can supply these values.

Here are a few examples. (Numbers with a plus sign are acidic; numbers with a minus sign are alkaline.)

2 ounces cheddar cheese:
PRAL = 0.49 (14) + 0.037 (286) - 0.021 (54.8) - 0.026 (15.6)
PRAL = +16 (very acidic)

3 ounce beef tenderloin, broiled:
PRAL = 0.49 (23) + 0.037 (180) - 0.021 (290) - 0.026 (19.6)
PRAL = +11 (very acidic)

2 slices whole wheat bread:
PRAL = 0.49 (8) + 0.037 (113) - 0.021 (139) - 0.026 (46)
PRAL = +4 (weakly acidic)

1 medium banana:
PRAL = 0.49 (1) + 0.037 (30) - 0.021 (487) - 0.026 (37)
PRAL = -10 (very alkalizing)

1 large sweet potato, baked in skin (about 1 cup):
PRAL = 0.49 (4) + 0.037 (108) - 0.021 (950) - 0.026 (54)
PRAL = -15 (very alkalizing)

Foods containing animal protein tend to be the most acid-forming. In general:

  • Dairy - Acidic
  • Meats (beef, poultry, pork, seafood) - Acidic
  • Grains (wheat, rice, corn) - Weakly Acidic
  • Beans and legumes - Slightly Alkaline to Slightly Acidic
  • Fats and Oils - Neutral
  • Fruits - Alkaline
  • Vegetables - Alkaline
1 Dietary Potential Renal Acid Load And Renal Net Acid Excretion In Healthy, Free-Living Children And Adolescents, American Journal of Clinical Nutrition, 2003