christopher vasey naturopathe


Controversy about the acid-alkaline balance:
are fruits alkalizing or acidifying?

Some therapists claim that fruits are alkalising. They recommend eating many of them or to follow a lemon juice cure, a grapes cure, apple cure etc. Other practitioners on the contrary maintain that fruits are acidifying and that it would be better to avoid them or to eat only small quantities of them. Who is right? How can these opposite opinions coexist?

Weak and strong acids

To find the answer to the question, one must be aware that in addition to the degree of acidity measured by the pH scale, acids can be characterized as either strong or weak. In fact, acids are rarely encountered in a free or isolated state; they are most often combined with an alkaline element. When the alkaline combined with the acid is strong (chemically speaking), the acid is of little consequence in the combination. The acid is called weak, as it is easy for the body to reject it. When the alkaline element is weak, however, the acid content is of much greater consequence. It is stable and mixes poorly with other elements, and it is referred to as strong.

Physiologically, strong acids – precisely because of their stability and resistance to combining – are much more difficult to neutralize and eliminate from the body than weak acids.

Strong acids come primarily from animal proteins. They chiefly consist of uric, sulphuric, and phosphoric acids. Their elimination from the body requires significant neutralization, a task performed by the liver as well as the normal elimination work of the kidneys. Because the kidneys can only eliminate a fixed amount of strong acids on a daily basis, however, any excess is stored in the tissues. Consequently, it is important to monitor the consumption of animal proteins.

But it is the weak acids that we were concerned about. They are primarily of plant origin (carbohydrates and vegetable proteins), except for those coming from yogurt and whey, which are of animal origin. Weak acids include citric, oxalic, pyruvic, and acetylsalicylic acids. Weak acids are also called volatile acids, because once they have been oxidized they are eliminated by the lungs in the form of vapors and gases, both as breath moisture and as carbon dioxide (CO2). Volatile acids are primarily regulated by respiratory function, as opposed to fixed acids, which can only be regulated by the kidneys and eliminated from the body in fluid form. The volatile acids elimination is therefore relatively easy, and there are no limits on the quantity that can be expelled from the body by the kidneys, unlike non-volatile strong acids. When the body needs to increase the elimination of volatile acids, it does so simply by increasing the rate of respiration. The amount of volatile acids that can be eliminated is limited only by how fast and how deeply a person is able to breath.

Many people however metabolize very poorly weak acids.

The metabolic weakness toward acids

Some illnesses arise because a person's body is unable to properly metabolize a particular nutrient. Partially or completely unmetabolized nutrients stagnate in the body, causing it to fall ill either through their own toxic effects or by disrupting the body's functioning. In diabetes, for example, the substance that is poorly metabolized is sugar; in rheumatism it is proteins; in obesity it is fat; in celiac disease it is gluten; and in water retention it is salt. These are just a few of the many substances, acids among them, that the body may have trouble metabolizing.

Difficulty metabolizing acids primarily involves weak acids. Weak acids are normally quite easy to oxidize, and their elimination through the lungs in the form of carbon dioxide or breath moisture makes the strong alkaline substances with which they are combined available for the body's use. As a rule, foods rich in weak acids, such as fruits, whey, yogurt, and vinegar, contribute a large number of alkaline elements to the body. But this is not always true for everyone, specifically that category of people whose metabolisms have trouble oxidizing weak acids.

For such people, weak acids are poorly oxidized, if at all, and they remain in the body without releasing the alkaline substances with which they are combined. In people with this metabolic weakness, foods that would normally contribute a high quota of alkaline substances instead have the effect of acidifying the internal environment. The same food can have an entirely different effect depending on the body of the person who ingests it. This is why some dietitians declare that lemon is an alkalizing food while others claim it is acidifying. Both are correct. The error lies in not determining whether the physical constitution of the person eating the food has an inherent metabolic weakness toward acids.

To adapt to our metabolic abilities

People afflicted with this metabolic debility must take additional precautions with their diet. It is essential that they carefully regulate the amount of foods they eat that are rich in weak acids (see chart below).

Normally, this group of weak-acid foods doesn't figure in the classification set up to help people maintain their acid-alkaline balance. Foods are generally divided into only two groups: acidifying and alkalizing foods, since with their weak acids they have an alkalizing effect on most people. But the lack of a third list of weak-acid foods could lead to serious problems for individuals whose Achilles'heel is metabolizing weak acids. They could consume large quantities of fruits, vinegar, and so on, confident they were alkalizing their internal environments, whereas in fact they would be creating precisely the opposite effect.

Chart of weak-acid foods

  • Unripe fruits (the less ripe a fruit, the higher its acid content)
  • Acid fruits: berries (red and black currants, rasberries, strawberries);
    citrus fruits (lemon, grapefruit, tangerines, oranges); certain varieties of apples
  • (winesap), cherries (Morello), plum, apricots
  • Sweet fruits (especially when eaten in excess), melon, watermelon
  • Acid vegetables: tomato, rhubarb, sorrel, watercress
  • Sauerkraut, vegetables that have been lactofermented (cultured with lactobacillus)
  • Fruit juices, lemon juice (in salad)
  • Whey, yogurt, curds, small-curd cottage cheese
  • Honey
  • Vinegar

This group of foods consists of foods whose alkalizing or acidifying effect depends on the metabolic capacities of the person who eats them. Their classification is therefore not based upon their physical effect (because that cannot be defined in advance) but on the basic nature of their acids, which are weak acids.

Detecting inability to metabolize acids

One way of detecting this inability is to temporarily increase your intake of weak-acid foods such as fruits, yogurt, … to see if this leads or not to an increase of your acidifying health problems. The purpose of this "challenge" test is not to make you sick, but simply to confirm or rule out the possibility that you have a deficiency in metabolizing weak acids.

If you have such a deficiency, a more significant intake of weak acids should cause joint pains to intensify, red blotches on the skin to grow larger, fatigue to become more noticeable, and nervousness, burning urination, itching, and other symptoms to increase.

This test involves consuming generous helpings of fresh fruit, fruits juices, and so forth for one or two days. This is long enough to bring about noticeable aggravation of symptoms. If you are extremely sensitive, the negative effects of acids may manifest as quickly as a half an hour after consumption. You will experience a general sense of feeling unwell and a sudden fatigue, and your teeth may feel on edge on response to the aggressive acids.

Fortunately, it is not often necessary to perform this test. It is usually enough to recall what happened in the past under similar circumstances. For example, you may have seen negative effects after you ate a large quantity of fruit when it was in season, or a significant quantity of vinegar or yogurt. If you underwent a grape or lemon juice fast in the past, did it have a beneficial effect on your general health, restore your strength, and bring about the disappearance of illnesses? Or did it accentuate your symptoms and reduce your vitality?

In the first instance there is no case of metabolic deficiency regarding acids, and it is clear that the primary causes for your state of acidification are acidifying foods (meat, sugar, fats, cereal grains, …and lifestyle choices. You can therefore eat weak-acid foods, for they will have an alkalizing effect.

In the second instance, though, it would be clear that you have a metabolic weakness. You can assess the degree of the problem by the intensity of the aggravation of your symptoms. You should keep close watch not only over the quantity of acidifying foods in your diet, but also the amount of weak-acid foods you consume.

Christopher Vasey