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.
The alkaline diet is also known as the acid-alkaline diet or alkaline ash diet.
Its premise is that your diet can alter the pH value — the measurement of acidity or alkalinity — of your body.
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, the chemical reactions in your body happen in a slow and controlled manner.
When things burn, an 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, if you eat foods that leave acidic ash, it 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 is thought to make 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 an acidic ash include protein, phosphate, and sulfur, while alkaline components include calcium, magnesium, and potassium ( 1 , 2 ).
Certain food groups are considered acidic, alkaline, or neutral:
- Acidic:
- Neutral:
- Alkaline:
Summary
When discussing the alkaline diet, it’s important to understand pH.
Put simply, pH is a measurement of how acidic or alkaline something is.
The pH value ranges from 0–14:
- Acidic:
- Neutral:
- Alkaline (or basic):
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 ( 3 ).
When your blood pH falls out of the normal range, it can be fatal if left untreated ( 4 ).
However, this only happens during certain disease states, such as ketoacidosis caused by diabetes, starvation, or alcohol intake ( 5 , 6 , 7 ).
Summary
It’s critical for your health that the pH of your blood remains constant.
If it were to fall outside of the normal range, your cells would stop working and you would die very quickly if untreated.
For this reason, your body has many effective ways to closely regulate its pH balance. This is known as acid-base homeostasis.
In fact, 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 ( 1 , 8 ).
Excreting acids in your urine is one of the main ways your body regulates its blood pH.
If you eat a large steak, your urine will be 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
Osteoporosis is a progressive bone disease characterized by a decrease in 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.
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 closely manage blood pH ( 9 ).
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 bone ( 10 , 11 ).
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 ( 12 ).
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 ( 13 , 14 , 15 , 16 , 17 ).
Clinical trials, which tend to be more accurate, have concluded that acid-forming diets have no impact on calcium levels in your body ( 9 , 18, 19 ).
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 ( 20 , 21 ).
As such, a high-protein, acid-forming diet is likely linked to better bone health — not worse.
Summary