christopher vasey naturopathe
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Why are there differences between authors’ lists
about the acid or alkaline effect of food ?


In the past, before chemistry developed enough to carry out accurate analysis of food composition, the alkaline or acidic characteristics of the different foods were established by observation of the patient's reaction to them that is by clinical evidence. The lists established by various practitioners were very similar. Things changed when chemical analysis were carried out. The results were very often contradictory to the list established by clinical evidence. Why is that, why are there differences between author's lists about the acid or alkaline effect of food?

The reason of the differences is that some practitioners go by charts based on food analysis or laboratory tests others by clinical evidence. To this must be added that some foods are impossible to classify in one category because, depending on who eats them, they can have an acidifying or an alkalising affect. This is the question of the weak acid foods (fruits, tomatoes …) which will be dealt with at the end of the article.

1. Food analysis

By burning a food, that is by breaking it down to its minutes parts, it is possible to analyze its acid and alkaline mineral content.

If a food has a higher content of acid minerals than alkaline one, it will be declared acidifying, and vice versa. Depending on the proportions of acid and alkaline minerals, it is also possible to give a figure to express how acidifying/alkalizing a food is in comparison to the others. The question here is: does a food get broken down as minutely during digestion in a human body which is overfed, tired, stressed, sick … as in a test tube? The answer is of course no.

That means that the alkaline content of a specific food will not be exploited to its maximum by the body (for example a part of the alkaline minerals will not even leave the intestines to penetrate in the blood and the cells, but will be eliminated by the bowels). In such a case the food will not be as alkaline as the chart shows. The same is also true for the acidifying foods.

The flaw in this approach is that it only considers the foods, without taking in account what will happen to them once they have entered the body and are digested and metabolized by it.

2. PRAL analysis

The aim of this system is to take in account what happens to the foods in the body. It measures the Potential Renal Acid Load, that is the quantity of acids evacuated by the kidneys in the urine after the consumption of different foods. A 100g of a specific food is therefore given to a volunteer. The urine content in acidic minerals (phosphorus, sulphur, chlorine, …) is then measured. The PRAL values which are acidic are shown by positive numbers (Cheddar cheese + 26,4; chicken + 8,7 …), the neutral ones by 0 (milk 0,7), and the alkaline ones by a negative figures (lettuce -2,5; potatoes -4; spinach -14). The higher the positive number, the higher the acidity, the lower de negative number, the higher the alkalinity.

A majority of PRAL values correspond to practice and clinical evidence, but some are totally in opposition to them. Well known acidifying food are claimed to be alkaline: jam -1,5; coffee -1,4; red wine -2,4; tomatoes -3,1 or neutral: coca-cola + 0,4.

Other foods which are well known to be alkaline are considered as acidic: almonds +4,3 and some alkaline waters: Contrex +3,9, Hépar + 4,35.

The existence of these unexplainable discrepancies should encourage us to be careful when using PRAL tables because they don't fully reflect the reality. It should also encourage us to recourse to the clinically established lists, as can be found in my book "The Acid-alkaline Diet". They are certainly less scientific, but closer to reality and more efficient in practice.

The issue of the weak acid foods

The weak acid foods are the fruits, tomatoes and vinegar. These foods contain a good deal of acid, hence their acidic taste. Because these acids are weak, people capable of metabolizing them properly will oxidize them easily. These weak acids therefore are transformed into alkaline elements and therefore contribute to the alkalization of the body. Some people however cannot metabolism weak acids properly. The large quantity of acids contained in these foods is not oxidized, they stay acid and they thus will have an acidifying effect.

For example, tomatoes and lemon juice are alkalizing for people who can easily oxidize the weak acids, but acidifying for the others.

Depending if the lists have been establishes by observing the reaction of people who oxidize weak acids or who don't, the foods will be classified as being alkaline or acidic.

Christopher Vasey