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The alkaline diet, or the alkaline ash diet or alkaline acid diet as it’s known in some circles, is based on the premise that acidic blood causes all sorts of health problems that can be countered by eating more alkaline foods. (Put a pin in the terms acidic and alkaline, because we’ll be covering the specifics on those in a bit.)
Proponents say that the alkaline diet can help you lose weight and stay strong against health conditions like arthritis and cancer.
Is it all it’s cracked up to be?
While the alkaline diet promotes many healthy foods—fruits, vegetables, and water galore—and cautions against the consumption of alcohol, sugar, and processed foods—nothing you eat is going to have a dramatic effect on the pH of your blood. Your body has mechanisms in place to keep blood pH regulated, and eating too many alkaline foods and not enough acidic foods may lead to amino acid nutritional deficiencies that can have disastrous consequences on your health.
pH is a measurement of how acidic or alkaline something is. The normal pH of the blood is around 7.4. Above that value is considered alkaline, and below that is considered acidic. Your stomach needs to be acidic (with a pH of 3.5 or below) to break down the foods you eat. The pH of urine changes according to your diet, and these pH changes in urine help keep your blood pH stable.
Predicated on the premise that maintaining the pH of the blood above 7.4 (i.e., alkaline) helps improve health, the alkaline diet recommends avoiding foods that may lower blood pH. In the alkaline diet, dietary proteins and amino acids, particularly animal protein, are especially to be avoided. The alkaline diet advocates eating non-acidic foods and even ingesting bicarbonate (HCO3–), which is a base that can neutralize acidic blood.
The alkaline diet is constructed on the notion that alkaline foods increase the pH of urine, thereby making urine less acidic. There are two problems with basing a dietary theory on urinary pH. First, urinary pH does not necessarily reflect blood pH. Second, there is no data to support the claim that acidic urine results in any adverse health outcomes.
The body absorbs essential amino acids needed for your survival from the proteins you eat. As you might guess, amino acids are acidic, and this is reflected by a drop in the pH of urine, reflecting a more acidic urine after you’ve consumed protein-rich foods.
The absorption of sulfur-containing amino acids, such as methionine and cysteine, is considered particularly problematic, as increased sulfur intake can result in the formation of sulfuric acid and present a significant acid load to the body. Animal proteins are a good source of sulfur-containing amino acids, which is why the alkaline diet cautions against the consumption of animal proteins.
There is an innate fallacy in this method, however. Sulfur plays many important roles in the body and sulfur deficiency can have many adverse effects. More directly to the point, dietary amino acids, including sulfur-containing amino acids, have only a transient effect on blood pH. This is because the body has a very effective system that regulates the pH of blood.
The kidneys play a role in maintaining a constant pH in the blood. When the blood becomes acidic after you ingest amino acids, the kidneys excrete ammonia in the urine, which tends to balance the acidic load in the blood.
Although your urine becomes more acidic after eating amino acids, acidic urine does not reflect acidity in the blood. Rather, urine is acidic to help prevent your blood from remaining acidic and to keep blood pH constant. This is a natural function of the kidneys, and there is no evidence that high protein or amino acid intake has any detrimental effect on the kidneys.
The excretion of ammonia in the urine is only a minor player in keeping blood pH in the normal range. The major mechanism for keeping blood pH properly balanced is the bicarbonate system.
The pH balance of the blood is maintained predominantly by the lungs. The lungs excrete protons derived from dietary metabolism of acids as carbon dioxide (CO2) in the breath. The CO2 in the blood is in equilibrium with bicarbonate (HCO3–)—as the HCO3– neutralizes extra acid, more CO2 is produced and excreted in the breath. The HCO3– used is regenerated in the kidneys. This is a very efficient process that keeps blood pH tightly regulated, even after you consume a large amount of protein and/or amino acids.
The alkaline diet does not account for the efficient regulation of blood pH by the bicarbonate system and by urinary excretion of ammonia.
FACT: Consuming animal protein and/or amino acids does not acidify the blood significantly, so there is no physiological basis for the alkaline diet.
On the other hand, following the recommendation of the alkaline diet to avoid animal proteins and sulfur-containing amino acids will result in an inadequate intake of essential amino acids (amino acids not produced in the body) that have a wide range of important metabolic functions.
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