The Collison Newsletter October 2010


                     PRAL - Potential Renal Acid Load

    A Measure of the Effect of Foods on the pH of the Body*   


Potential Renal Acid Load (PRAL) is a calculated value of certain nutrients in food that have the most significant indication of changing the acidity or alkalinity of the body.

Acid Alkali Balance - The Ideal Diet 

My September 2005 newsletter Acid Alkali Balance – the Ideal Diet pointed out that “The absolute foundation of sound nutrition is to maintain the correct acid/alkali balance in the body.” The ideal diet should consist of 75%-80% alkali-forming foods, ie foods that have an alkali residue after metabolism.


In general terms:

·        Alkali-forming foods include most fruits, most vegetables (especially greens), some beans, lentils and some nuts.

·        Acid-forming foods include meats (beef, lamb, pork, poultry), fish, dairy products (especially cheeses), most grains (especially if refined) and processed foods.


The newsletter Acid Alkali Balance - The Ideal Diet sets out the following six groupings of foods and lists the various foods in each group:

·        High alkali-forming foods

·        Moderate alkali-forming foods

·        Low alkali-forming foods

·        Low acid-forming foods

·        Moderate acid-forming foods

·        High acid-forming foods.


The foods listed in the various groups were compiled from multiple published sources. There was agreement on most foods. However, there was a degree of unsurity as to the acid/alkali characteristics of some foods. The calculations made by most of these investigators were based on acid-alkaline ash analyses of the individual foods.


The above groups are still the basis for determining a diet of 75%-80% alkali-forming foods, the ideal diet. It is recommended that the 20% - 25% acid-forming foods should come from the low and moderate acid-forming groups, avoiding all foods listed in the high acid-forming group.

Potential Renal Acid Load - PRAL 

pH (potential of hydrogen) is a measure of the acidity or alkalinity of a solution. It is a measure of hydrogen ion concentration. It is expressed on a scale of 0-14. The lower the pH, the more acidic is the solution, the higher the pH, the more alkaline (or base) the solution. When the solution is neither acid nor alkaline, it has a pH of 7, which is neutral. It is a logarithmic scale.


The human blood must stay in a narrow pH range (7.35-7.45). The proper alkaline pH of the blood is critical for the overall health of the body. Any excess acid waste in the body has to be excreted to maintain the safe and healthy alkaline blood levels. This takes place via the kidneys, giving acidic urine.


Potential renal acid load experiments show that PRAL is a reliable approximation of the pH effect of foods in the body.


PRAL is based on the original work of Drs Thomas Remer and Friedrich Manz. Their paper, Potential renal acid load of foods and its influence on urine pH, was published in the Journal of the American Dietetic Association, in July 1995 (95: 791-797).


“The purpose of this study was to calculate the potential renal acid load (PRAL) of selected, frequently consumed foods. A physiologically based calculation model was recently validated to yield an approximate estimate of renal net acid excretion (NAE); the model depends primarily on nutrient intake data. When nutrient data from actual food composition tables were used, the calculation model yielded PRAL values that ranged from an average maximum  of 23.6 mEq/100g for certain hard cheeses over 0mEq/100g for fats and oils to an average minimum of approximately -3mEq/100g for fruits and fruit  juices and vegetables. By means of these PRAL data (summed according to the amounts of foods and beverages consumed daily and by an estimate of excretion of organic acids [based on body size]), the daily NAE can be calculated. This calculation methodology, primarily based on PRAL, allows an approximate prediction of the effects of diet on the acidity of urine.”


Briefly, the method used for the calculation of the PRAL of foods was based on a model developed by the authors for prediction of NAE from nutrient intake data. The directly determined NAE, based on urine analysis, was calculated in the conventional manner as the sum of titratable acid and ammonium minus bicarbonate. NAE was also determined indirectly from the difference of the sum of the remaining important urinary anions (negative) [chloride, phosphorus, sulphate and organic acids (nonbiocarbonate anions)] minus the sum of the mineral cations (positive) [sodium, potassium, calcium and magnesium]. The amounts of these electrolytes in urine were determined primarily by nutritional intake. In the reported study, the average, absorbable amounts of all relevant nutrients (representing NAE without organic acids) were estimated for the selected foods and beverages from data on the nutrient composition of foods (per 100 gram edible portion) and from average net absorption rates (from the intestines) taken from the literature.


The authors state the following: “According to the calculation model described, negative PRAL values (indicating an excess of the base-forming potential of foods) were nearly exclusively found in the vegetable and fruit groups. In contrast, the highest acid loads originated in cheese, followed by meat, fish and grain products. Similar trends, although with marked deviations for individual foods, were observed by other investigators whose calculations were based on acid-alkaline ash analyses or on current food tables. However none of these researchers considered the (average) net absorption rates of the relevant minerals.”


More than 100 frequently consumed foods and beverages were studied. The maximum (acidic) PRAL was for parmesan cheese, 34.2mEq/100g, through 0mEq/100g for fats & oils to the lowest (minimum or alkaline) of -21.0mEq/100g for raisins. Among the raw (i.e. non-dried) fruits, the base-forming (alkaline) potential was similar to that of vegetables.


The following table sets out the average PRAL for certain food groups and combined foods (related to 100 gram edible portion):

Food GroupPRAL (mEq)
Fats and oils0
Fruits and fruit juices-3.1
Grain products: 
      Noodles, spaghetti6.7
Meat and meat products9.5
Milk and Dairy products: 
      Milk and non cheese products1.0
      Cheese with lower protein content8.0
      Cheese with higher protein content 23.6

The following is taken from Table 2 of the above article. It sets out the estimated potential renal acid load (PRAL) of 114 frequently consumed foods and beverages (related to 100 gram edible portion).

Food Group and FoodPRAL
      Beer, dark-0.2
      Beer, stout bottled-0.1
      Cocoa, made with semi skimmed milk-0.4
      Coffee, infusion 5 minutes-1.4
      Mineral water (Apollinaris)-1.8
      Mineral water (Volvic)-0.1
      Tea, Indian infusion-0.3
      White wine, dry-1.2
Fats and Oils 
      Butter 0.6
      Margarine -0.5
      Olive oil0.0
      Sunflower seed oil0.0
      Cod fillets 7.1
      Haddock 6.8
      Herring 7.0
      Trout, brown steamed10.8
Fruits, Nuts and Fruit Juices 
      Apple juice, unfiltered-2.2

      Apples, 15 varieties flesh and skin, average

      Apricots -4.8
      Bananas -5.5
      Black currants -6.5
      Cherries -3.6
      Grape juice, unsweetened-1.0
      Kiwi fruit-4.1
      Lemon juice-2.5
      Orange juice, unsweetened-2.9
      Oranges -2.7
      Peaches -2.4
      Pears, 3 varieties flesh and skin, average-2.9
      Pineapple -2.7
      Raisins -21.0
      Strawberries -2.2
      Watermelon -1.9
      Hazelnuts -2.8
      Walnuts 6.8
Grain Products 
      Bread, rye flour mixed4.0
      Bread, rye flour4.1
      Bread, wheat flour mixed3.8
      Bread, wheat flour whole meal1.8
      Bread, white bread3.7
      Cornflakes 6.0
      Crispbread, rye3.3
      Noodles, egg6.4
      Oat flakes, rolled oats10.7
      Rice, brown12.5
      Rice, white, easy cook4.6
      Rice, white, easy cook, boiled1.7
      Rye flour, whole5.9
      Spaghetti, white6.5
      Spaghetti, whole meal7.3
      Wheat flour, white plain6.9
     Wheat flour, whole meal8.2
      Beans, green/French beans-3.1
      Lentils, green and brown, whole, dried3.5
      Peanuts, plain8.3
Meat and Meat Products 
      Beef, lean only7.8
      Chicken, meat only8.7
      Corned beef, canned13.2
      Frankfurters 6.7
      Liver sausage10.6
      Luncheon meat, canned10.2
      Pork, lean only7.9
      Rump steak, lean and fat8.8
      Salami 11.6
      Turkey, meat only9.9
      Veal, fillet9.0
Milk and Dairy Products 
      Buttermilk 0.5
      Camembert cheese14.6
      Cheddar cheese, reduced fat26.4
      Cheese, Gouda18.6
      Cottage cheese, plain8.7
      Creams, fresh, sour1.2
      Fresh cheese, (Quark)11.1
      Full-fat, soft cheese 4.3
      Hard cheese, average 4 types19.2
      Ice cream, dairy, vanilla0.6
      Whole milk, evaporated1.1
      Whole milk, pasteurised0.7
      Parmesan cheese34.2
      Yogurt, whole milk, fruit1.2
      Yogurt, whole milk, plain1.5
      Eggs, chicken, whole8.2
      Egg white1.1
      Egg yolk23.4
Sugar, Preserves and Sweets 
      Chocolate, milk2.4
      Honey -0.3
      Madeira cake3.7
      Marmalade -1.5
      Sugar, white-0.1
      Broccoli -1.2
      Carrots, young-4.9
      Celery -5.2
      Chicory -2.0
      Cucumber -0.8
      Eggplant -3.4
      Leeks -1.8
      Lettuce, average 4 varieties-2.5
      Lettuce, iceberg-1.6
      Mushrooms, common-1.4
      Onions -1.5
      Peppers, green-1.4
      Potatoes, old-4.0
      Radish, red-3.7
      Spinach -14.0
      Tomato juice-2.8
      Tomatoes -3.1
      Zucchini -4.6


In general terms, the data from PRAL agrees with the data based on acid-alkaline ash analyses. There are, however, some results that are at variance. For example coffee has a PRAL value of -1.4, ie an alkali residue, whereas it is generally accepted as being a high acid-forming food. The same result occurs with beers (PRAL -0.2, 0.9, -0.1) when beer is normally considered to be a high acid-forming food. Another unexpected result was for sugar (PRAL -0.1), when it, and foods containing sugar such as chocolate (PRAL 2.4), are regarded as high acid-forming foods. An explanation for this disparity is based on the different ways in which the data is obtained. PRAL is closely linked to the presence of minerals and trace elements in the particular food, such as chloride, phosphorus, sulphate, sodium, potassium, calcium and magnesium. White sugar, for example, is a pure crystalline carbohydrate, sucrose (C6H12O6), and as such has no minerals or trace elements associated with it.


The Potential Renal Acid Load (PRAL) for the foods and beverages as set out above confirms that:

·        alkali-forming foods are fruit and vegetables

·        acid-forming foods are meat, fish, cheese, grains and salted processed foods.


The tables, as set out in my September 2005 newsletter Acid Alkali Diet - The Ideal Diet, and the PRAL information of this newsletter will enable you to select foods to achieve the aim of the ideal diet, namely 75%-80% of foods to be alkali-forming.


In my March 2009 newsletter Foods for Health, the simple answer to the question “How do I make the transition from my ‘bad’ diet to the recommended healthy diet?” is given as follows: Progressively reduce the intake of all animal foods, ideally to zero. This will mean an increasing intake of vegetarian foods. The more of these that are raw, the better. Exclude all processed and refined foods and foods that have had chemicals (preservatives, flavours etc) added to them”.


*Copyright 2010: The Huntly Centre.

Disclaimer: All material in the website is provided for informational or educational purposes only. Consult a health professional regarding the applicability of any opinions or recommendations expressed herein, with respect to your symptoms or medical condition.  


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