Thursday, June 24, 2010

Acid-Producing Diets

Note about photo: Squash reduce acid load and are beneficial.

Diets that present more acid than alkaline to our kidneys may:
  • Promote insulin resistance1
  • Lower vitamin D levels1
  • Cause loss of minerals from the skeleton, contributing to osteoporosis. (Minerals are used by the body, in compounds like calcium bicarbonate, to neutralize acid.)
They may also be responsibe for other things I'm still reading about:
  • Muscle wasting
  • Reduced capacity for exercise
Those shockingly healthy soccer players down at the World Cup right now probably share the secret of sodium bicarbonate to neutralize body acid, improving athletic performance.

What Is An Acid-Producing Diet?

An acid-producing diet is one that, once digested and metabolized, pushes body fluids to a lower, or more acidic, pH. (The body maintains blood in a tight, slightly alkaline pH range of 7.35 to 7.45.)

The pH of a food does not indicate its pH effect on the body. Acidic citrus fruits, for example, have an alkalizing effect ... eating a lemon will not make the blood more acidic.

The Potential Renal Acid Load (PRAL) is an equation used to estimate how acid-forming a diet is. (It appears to have been developed by Thomas Remer in the early 1990s.2)
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)1

*Protein is used as an estimate for sulfate. Protein is made up of amino acids. Of the 20 common protein-sourced amino acids in food, only 2 contain sulfur: methionine and cysteine.
Just looking at that equation, you can tell (by the positive or negative signs) that:
  • Foods high in protein are more acid-producing (especially proteins high in sulfur).
  • Foods high in phosphorous are more acid-producing.
  • Foods high in potassium are more alkaline-producing.
  • Foods high in magnesium are more alkaline-producing.
  • Foods high in calcium are more alkaline-producing.
Looking at the coefficients, you can tell that foods high in protein pull the most weight. Phosphorous, potassium, magnesium and calcium have much less of an effect. In fact, Remer et al. found that eliminating calcium from the equation actually improved prediction of acid effect - including calcium tended to underestimate acid load.3

I was going to plug some foods into this equation but the authors of GoutPal did such a beautiful job of that already:
Acid / Alkali Food Tables

  • Dairy - Acidic
  • Meats (beef, poultry, pork, seafood) - Acidic
  • Grains (wheat, rice, corn) - Acidic (not as acid as dairy and meat)
  • Beans and legumes - Slightly alkaline to slightly acidic
  • Fats and Oils - Neutral
  • Fruits - Alkaline
  • Vegetables - Alkaline
The acid-forming potential of a food also depends on how much of it you eat. You can go to a database like and pick up protein, phosphorus, etc. of a food you like, in the amount you eat it, plug it in the equation, and see its effect.

For example (positives are acid, negatives are alkaline):

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

1 ounce cheddar cheese:
PRAL = 0.49 (7) + 0.037 (143) - 0.021 (27.4) - 0.026 (7.8)
PRAL = +8 (very acidic)

1 large egg, hard-boiled:
PRAL = 0.49 (6) + 0.037 (86) - 0.021 (63) - 0.026 (5)
PRAL = +5 (acidic)

1 cup brown rice, cooked:
PRAL = 0.49 (5) + 0.037 (150) - 0.021 (154) - 0.026 (85.8)
PRAL = +2.5 (slightly acidic)

1 small box (1.5 oz) seedless raisins:
PRAL = 0.49 (1) + 0.037 (43.4) - 0.021 (322) - 0.026 (13.8)
PRAL = -5 (alkalizing)

1 cup butternut squash, baked:
PRAL = 0.49 (2) + 0.037 (55.4) - 0.021 (582) - 0.026 (59.4)
PRAL = -11 (very alkalizing)

1 sweet potato, baked in skin (large, about 1 cup, 200g):
PRAL = 0.49 (4) + 0.037 (108) - 0.021 (950) - 0.026 (54)
PRAL = -15 (very alkalizing)

These are just estimates. We can't know the real-time constituents of a food. We can't know the absorption of those constituents in a given individual. We can't know the buffering ability of an individual's blood at any given time.

I should note - other things besides diet affect the pH of body fluids. Excessive exercise lowers pH (low pH is acidic), as does the inability to remove carbon dioxide by effective breathing (lung diseases foster lower pH).

One good thing ... You can combine acid-forming foods with alkaline-forming foods and break even.

A diet that emphasizes fruits and vegetables, and that minimizes meat and dairy foods (such as the Paleo Vegetarian Diet), is a low-acid-forming diet that may reduce the risk for insulin resistance (and so diabetes), osteoporosis, age-related muscle wasting, and other pH sensitive conditions.

1 Effect Of Metabolic Acidosis On Insulin Action And Secretion In Uremia, Kidney International, 1998
2 Potential Renal Acid Load Of Foods And Its Influence On Urine pH, Thomas Remer and Freidrich Manz, Journal of the American Dietetic Association, 1995
3 Dietary Potential Renal Acid Load And Renal Net Acid Excretion In Healthy, Free-Living Children And Adolescents, American Journal of Clinical Nutrition, 2003

Photo from my 2005 Farmers' Market Tour.


caulfieldkid said...

Interesting. The foods are not intuitive as to their alkaline or acidic producing effects. I checked cider vinegar (common home remedy for just about anything you want to believe). It's alkaline producing. Vinegar to alkaline. Go figure.

- shaun

Bix said...

It's so weird, isn't it. It's counterintuitive.

I think this is a reason why women in developing countries who have low calcium intake still have high bone density and lower incidence of osteoporosis.

Dr. Mel said...

"Just looking at that equation, you can tell..."--easy for you to say! Not so easy for us non-mathematical types! But you give a very clear explanation--that's one of the things I love about this blog.
Several decades ago, I first heard about this in the advertising for a beverage that was supposed to reduce your body's acidity. It was indeed fascinating to learn that things one would think of as acidic actually promoted an alkaline state--a real eye opener. Wish I could remember the name of the beverage--it was delicious (albeit expensive).

GoutPal said...

"One good thing ... You can combine acid-forming foods with alkaline-forming foods and break even"

Actually, it's vital to combine them. Recommendations vary between 20% and 33%, but we must have some acid foods to get a healthy nutrient balance.

On the counterintuitive acid-producing-alkali issue, it's because the acids, e.g. citric acid in lemons and acetic acid in vinegar, are very weak acids. The alkalizing components in the fruits do not register on a pH test, or our taste buds. This all changes as we digest the food, and the alkalizing components combine with acid compounds in or bodies, thus reducing the acid load at the kidneys.

Bix said...

GoutPal, you explained that really well. I appreciate it. And kudos on all the work you did!