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The alkaline diet: a science-based review

Die basische Ernährung: Ein wissenschaftsbasiertes Review

The alkaline diet is based on the idea that replacing acid-forming foods with alkaline foods can improve health. Advocates of this diet even claim that it can help fight serious diseases such as cancer.

This article will take a closer look at the science behind the alkaline diet.

What is the alkaline diet?

The basic premise of the alkaline diet is that your diet can change the pH level - which is a measure of acidity - of your body. Your metabolism - the conversion of food into energy - is sometimes described as a fire. Both involve chemical reactions that break down a solid mass.

However, the chemical reactions in your body occur in a slow and controlled way. When things burn, an ash residue is left behind. In a similar way, the foods you eat also leave behind "ash" residue, known as metabolic waste products.

As it turns out, these metabolic waste products can be alkaline - also known as neutral - or acidic. Alkaline diet advocates claim that metabolic waste products can directly influence the acidity of your body.

In other words, this would mean that if you eat foods that leave acidic ash behind, this would make your blood acidic. Eating foods that leave behind alkaline ash, on the other hand, would make your blood more alkaline.

Supporters of the acid-ash hypothesis believe that acidic ash makes you more susceptible to disease, while alkaline ash is considered protective. By choosing more alkaline foods, according to this hypothesis, you should be able to create a more alkaline environment in your body and improve your health.

Foods thought to leave acidic ash include protein, phosphates and sulfur, while alkaline compounds include calcium, magnesium and potassium (1, 2).

Certain food groups are considered acidic, alkaline or neutral:

  • Acidic: Meat, poultry, fish, dairy products, eggs, grains and alcohol.
  • Neutral: Natural fats, starch and sugar.
  • Alkaline: Fruit, nuts, legumes and vegetables.

Summary: According to alkaline diet advocates, the metabolic waste products - or ashes - left in the body when food is burned can directly affect the acidity of the blood.

Regulating pH levels in the body

When talking about alkaline nutrition, it is important to understand the concept of pH. Simply put, pH is a measure of how acidic or alkaline something is.

The pH ranges from 0 to 14:

  • Acidic: 0.0-6.9
  • Neutral: 7.0
  • Alkaline: 7.1-14.0

Many advocates of this diet recommend monitoring the pH of urine and making sure it is alkaline (above 7) and not acidic (below 7). However, it is important to note that pH varies greatly within the body. While some areas are acidic, others are alkaline - so there is no fixed value.

Your stomach is overloaded with hydrochloric acid, which gives the area around the stomach a pH of 2 to 3.5, which is very acidic. This level of acidity is necessary to break down food. Human blood, on the other hand, is always slightly alkaline and has a pH value of 7.36 to 7.44 (3). If the pH of the blood falls outside this normal range, it can be fatal if not treated (4).

However, this only happens in the context of certain disease states - such as ketoacidosis in diabetes, during starvation or under the influence of alcohol consumption - and has little to do with your diet (5, 6, 7).

Summary: The pH value measures the acidity of a substance. In the body, there are areas with an acidic environment, such as the stomach, and areas with an alkaline environment, such as the blood.

Food affects the pH of urine, but not the pH of blood

It is essential for health that the pH of the blood remains constant. If it were outside the normal range, the body's cells would stop functioning and you would die very quickly if this were left untreated.

For this reason, the body has many effective ways to regulate its pH balance very tightly. This is also known as the acid-base balance.

In fact, in healthy people, it is almost impossible to change the pH of the blood through food, although minimal fluctuations within the normal range can occur. However, food can definitely change the pH of urine, although this effect is variable (1, 8).

The excretion of acids via the urine is one of the main mechanisms by which the body regulates its pH. If you eat a large steak, your urine will be more acidic a few hours later as your body excretes metabolic waste products through the urine. For this reason, urine pH is a poor indicator of body-wide pH and overall health. In addition, urine pH can also be influenced by factors other than diet.

Summary: Your body regulates blood pH very closely. In healthy people, diet has no significant effect on blood pH - but it can change the pH of urine.

Acid-forming foods and osteoporosis

Osteoporosis is a progressive bone disease characterized by a reduced mineral content of the bones. This disease is particularly prevalent among postmenopausal women and can dramatically increase the risk of bone fractures.

Many alkaline diet advocates believe that in order to maintain a constant blood pH, your body uses alkaline minerals such as calcium from your bones to buffer the acids produced by eating acid-forming foods.

According to this theory, acid-forming diets such as the Western diet will cause a reduction in bone mineral density. This theory is also known as the "acid-ash hypothesis of osteoporosis". However, this theory ignores the function of the kidneys, which are crucial for the excretion of acid and the regulation of pH. The kidneys produce bicarbonate ions, which neutralize acids in the blood and allow your body to tightly control the pH of the blood (9).

Your respiratory system is also involved in controlling blood pH. When bicarbonate ions from the kidneys bind acids in the blood, carbon dioxide is produced which is excreted through the lungs and water is excreted through the urine.

The acid-ash hypothesis also ignores one of the most important factors in the development of osteoporosis - a loss of protein collagen from the bones (10, 11). Ironically, this loss of collagen is associated with low levels of two acids - silicic acid and ascorbic acid or vitamin C - in the diet (12).

You should also keep in mind that scientific research linking dietary acids to bone density or fracture risk has mixed results. While many observational studies have found no association, others have identified a significant link (13, 14, 15, 16, 17).

Clinical studies, which tend to be more accurate, have concluded that acid-forming diets have no effect on calcium levels in the body (9, 18, 19). If anything, these diets actually improve bone health by increasing calcium retention and activating the IGF-1 hormone, which stimulates muscle and bone repair (20, 21).

As such, a high-protein, acid-forming diet is likely to be associated with better bone health.

Summary: Although the evidence is mixed, most studies do not support the theory that acid-forming diets damage bone. Protein, an "acidic" nutrient, actually appears to be beneficial in this regard.

Acids and cancer

Many people claim that cancer only grows in an acidic environment and can be treated or even cured by an alkaline diet. However, more comprehensive studies of the relationship between diet-induced acidosis - or a diet-induced increase in blood acidity - and cancer conclude that there is no direct link (22, 23).

First of all, diet does not significantly affect blood pH (8, 24). And even assuming that food could dramatically alter the pH of blood or different body tissues, cancer cells are not restricted to an acidic environment.

Cancer grows in normal body tissue, which has a slightly alkaline pH of 7.4. In many experiments, cancer cells have been made to grow in an alkaline environment (25). And even if tumors grow faster in an acidic environment, tumors generate their own acids. It is not the acidic environment that generates the cancer - it is the cancer that generates an acidic environment (26).

Summary: There is no link between an acid-forming diet and cancer. Cancer cells also grow in an alkaline environment.

The diet of our ancestors and acidity

An examination of the acid-base theory from an evolutionary and scientific perspective reveals discrepancies. A study that estimated that 87% of pre-agricultural humans followed an alkaline diet forms the central argument supporting the modern alkaline diet (27).

More recent studies, however, estimate that half of pre-agricultural people followed a net alkaline diet, while the other half followed a net acidifying diet (28).

In this context, it should be kept in mind that our ancestors lived in very different climates with access to very different food supplies. Acid-forming diets were more common among people living further north of the equator, outside the tropical range (29).

Despite the fact that about half of hunter-gatherer cultures followed a net acidifying diet, modern diseases were much less common among these peoples (30).

Summary: Recent studies suggest that about half of our early ancestors followed an acidifying diet, which is especially true for people who lived farther from the equator.


An alkaline diet is quite healthy as it encourages the consumption of fruits, vegetables and healthy plant foods while minimizing processed junk food.

However, the view that this diet promotes health due to its alkalizing effects is suspect. These claims are not supported by reliable human studies,

However, some studies suggest positive effects in a very small group of people - those suffering from chronic kidney disease may benefit from an alkaline diet that is low in protein (31).

In general, however, the alkaline diet is only healthy because it is based on whole and unprocessed foods. There is no reliable evidence to suggest that this has anything to do with pH.




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