The alkaline diet is based on the idea that replacing acid-forming foods with alkaline foods can improve your health.
Proponents of this diet even claim that it can help fight serious diseases like cancer.
This article examines the science behind the alkaline diet.
What is the alkaline diet?
The alkaline diet is also known as the acid-alkaline or alkaline ash diet.
Its premise is that your diet can alter your body’s pH value — the measurement of acidity or alkalinity —.
Your metabolism — the conversion of food into energy — is sometimes compared to fire. Both involve a chemical reaction that breaks down a solid mass.
However, your body’s chemical reactions happen slowly and in a controlled manner.
When things burn, ash residue is left behind. Similarly, the foods you eat leave an “ash” residue known as metabolic waste.
This metabolic waste can be alkaline, neutral, or acidic. Proponents of this diet claim that metabolic waste can directly affect your body’s acidity.
In other words, eating foods that leave acidic ash makes your blood more acidic. If you eat foods that leave alkaline ash, it makes your blood more alkaline.
According to the acid-ash hypothesis, acidic ash makes you vulnerable to illness and disease, whereas alkaline ash is considered protective.
By choosing more alkaline foods, you should be able to “alkalize” your body and improve your health.
Food components that leave acidic ash include protein, phosphate, and sulfur, while alkaline components include calcium, magnesium, and potassium.
Certain food groups are considered acidic, alkaline, or neutral:
- Acidic: meat, poultry, fish, dairy, eggs, grains, alcohol
- Neutral: natural fats, starches, and sugars
- Alkaline: fruits, nuts, legumes, and vegetables
Summary: According to proponents of the alkaline diet, the metabolic waste — or ash — left from the burning of foods can directly affect the acidity or alkalinity of your body.
Regular pH levels in your body
When discussing the alkaline diet, it’s important to understand pH.
pH is a measurement of how acidic or alkaline something is.
The pH value ranges from 0–14:
- Acidic: 0.0–6.9
- Neutral: 7.0
- Alkaline (or basic): 7.1–14.0
Many proponents of this diet suggest that people monitor the pH of their urine to ensure that it is alkaline (over 7) and not acidic (below 7).
However, it’s important to note that pH varies greatly within your body. While some parts are acidic, others are alkaline — there is no set level.
Your stomach is loaded with hydrochloric acid, giving it a pH of 2–3.5, which is highly acidic. This acidity is necessary to break down food.
On the other hand, human blood is always slightly alkaline, with a pH of 7.36–7.44.
When your blood pH falls below the normal range, it can be fatal if left untreated.
However, this only happens during certain disease states, such as ketoacidosis caused by diabetes, starvation, or alcohol intake.
Summary: The pH value measures a substance’s acidity or alkalinity. For example, stomach acid is highly acidic, while blood is slightly alkaline.
Food affects the pH of your urine, but not your blood
It’s critical for your health that the pH of your blood remains constant.
If it were to fall outside the normal range, your cells would stop working, and you would die very quickly if untreated.
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For this reason, your body has many effective ways to regulate its pH balance closely. This is known as acid-base homeostasis.
It’s nearly impossible for food to change the pH value of blood in healthy people, although tiny fluctuations can occur within the normal range.
However, food can change the pH value of your urine — though the effect is somewhat variable.
Excreting acids in your urine is one main way your body regulates blood pH.
Eating a large steak will make your urine more acidic several hours later as your body removes the metabolic waste from your system.
Therefore, urine pH is a poor indicator of overall body pH and general health. It can also be influenced by factors other than your diet.
Summary: Your body tightly regulates blood pH levels. In healthy people, diet doesn’t significantly affect blood pH, but it can change urine pH.
Acid-forming foods and osteoporosis
Osteoporosis is a progressive bone disease characterized by decreased bone mineral content.
It’s particularly common among postmenopausal women and can drastically increase your risk of fractures.
Many alkaline-diet proponents believe that to maintain a constant blood pH, your body takes alkaline minerals, such as calcium, from your bones to buffer the acids from the acid-forming foods you eat.
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According to this theory, acid-forming diets, such as the standard Western diet, will cause a loss in bone mineral density. This theory is known as the “acid-ash hypothesis of osteoporosis.”
However, this theory ignores the function of your kidneys, which are fundamental to removing acids and regulating body pH.
The kidneys produce bicarbonate ions that neutralize acids in your blood, enabling your body to manage blood pH closely.
Your respiratory system is also involved in controlling blood pH. When bicarbonate ions from your kidneys bind to acids in your blood, they form carbon dioxide, which you breathe out, and water, which you pee out.
The acid-ash hypothesis also ignores one of the main drivers of osteoporosis — a loss in the protein collagen from the bone.
Ironically, this loss of collagen is strongly linked to low levels of two acids — orthosilicic acid and ascorbic acid, or vitamin C — in your diet.
Keep in mind that scientific evidence linking dietary acid to bone density or fracture risk is mixed. While many observational studies have found no association, others have detected a significant link.
Clinical trials, which tend to be more accurate, have concluded that acid-forming diets have no impact on calcium levels in your body.
If anything, these diets improve bone health by increasing calcium retention and activating the IGF-1 hormone, which stimulates the repair of muscle and bone.
A high-protein, acid-forming diet is likely linked to better bone health — not worse.
Summary: Although evidence is mixed, most research does not support the theory that acid-forming diets harm your bones. Protein, an acidic nutrient, even seems to be beneficial.
Acidity and cancer
Many argue that cancer only grows in an acidic environment and can be treated or even cured with an alkaline diet.
However, comprehensive reviews on the relationship between diet-induced acidosis — or increased blood acidity caused by diet — and cancer concluded that there is no direct link.
First, food doesn’t significantly influence blood pH.
Second, even if you assume that food could dramatically alter the pH value of blood or other tissues, cancer cells are not restricted to acidic environments.
Cancer grows in normal body tissue with a slightly alkaline pH of 7.4. Many experiments have successfully grown cancer cells in an alkaline environment.
And tumors grow faster in acidic environments, but they create this acidity themselves. It is not the acidic environment that creates cancer cells, but cancer cells that create the acidic environment.
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Summary: There is no link between an acid-forming diet and cancer. Cancer cells also grow in alkaline environments.
Ancestral diets and acidity
Examining the acid-alkaline theory from both an evolutionary and scientific perspective reveals discrepancies.
One study estimated that 87% of pre-agricultural humans ate alkaline diets, forming the central argument behind the modern alkaline diet.
More recent research approximates that half of the pre-agricultural humans ate net alkaline-forming diets, while the other half ate net acid-forming diets.
Remember that our remote ancestors lived in vastly different climates with access to diverse foods. Acid-forming diets were more common as people moved further north of the equator, away from the tropics.
Although around half of hunter-gatherers ate a net acid-forming diet, modern diseases are believed to have been much less common.
Summary: Current studies suggest that about half of ancestral diets were acid-forming, especially among people who lived far from the equator.
The alkaline diet is quite healthy, encouraging a high intake of fruits, vegetables, and healthy plant foods while restricting processed junk foods.
However, the notion that the diet boosts health because of its alkalizing effects is suspect. Any reliable human studies haven’t proved these claims.
Some studies suggest positive effects in a very small subset of the population. Specifically, a low-protein alkalizing diet may benefit people with chronic kidney disease.
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The alkaline diet is generally healthy because it’s based on whole and unprocessed foods. No reliable evidence suggests it has anything to do with pH levels.