Acid vs alkaline diets.  

 I’ve had a number of people ask me about the alkaline food diet, with questions about which foods are which and why an alkaline diet might be healthy. The most serious query was from a friend who asked if the so-called acid diet really was depleting the calcium from her bones. She has post-menopausal osteoporosis. 

On looking into this, it seems to be a good diet promoted for the wrong reasons. Reviews of the diet clearly show that acidic urine is not a sign of bone calcium depletion and that some of the acidic protein-rich foods are actually very healthy.

Acid and alkaline activity in chemistry is measured as pH (power of hydrogen, ie reactivity of the hydrogen atoms in a molecule). It is neutral at 7 (eg distilled water), acid at less than 7 (eg vinegar)  and alkaline at more than 7 (eg carb soda). My understanding of the acid-alkaline diet theory is that somehow foods form ash when burnt by the digestive system and this ash is acid when foods high in proteins (meat, diary, eggs) are consumed. Neutral ash is formed from sugars and fats and alkaline ash from fruits, nuts and vegetables. From my reading, these foods are supposed to change the pH of the whole body, implying a pH change in the blood and cell fluids. The good alkaline diet cures everything, the bad acid diet causes most diseases (cancer, diabetes, arthritis etc). The effects of the diet are measured by checking the pH of the urine on a daily basis.

The recommended diet does have good features, such as cutting down on highly processed foods and increasing the intake of fresh fruit, vegetables and nuts. Adding moderate amounts of dairy makes this a healthy vegetarian diet which would help prevent many chronic diseases. The problem is that the science behind the diet and its anti-protein argument is wrong and quite dangerous.


The science:

1.Ash (dictionary definition: the grayish-white to black powdery residue left when something is burned). Food is not burnt in digestion, it is broken down into small molecules that can be used for energy and to build body tissues. No ash is formed. 

a. Proteins are broken down into amino acids, to make new proteins that every cell in your body needs for maintenance and renewal. Meat, eggs and dairy are the only sources of complete proteins for humans. Plants contain proteins, but need to be carefully combined to provide a full set of essential amino acids.

b. Carbohydrates and fats are broken down into simple sugars and fatty acids and these are used for fuel in the cells. The byproducts of "burning" these fuels are carbon dioxide and water.

c. Waste products of digestion are removed as carbon dioxide via the lungs, fibre in the feces and urea in the urine. The urine is acid after a high protein meal and alkaline when mostly fruit and vegetables are eaten, but this pH changes with each meal and throughout the day.

2. Acid/alkaline pH balance in the body

a. Blood and body fluids are always alkaline. Our body maintains a very strict acid/alkaline balance in the blood and cell fluid by feedback-control systems with lungs, liver and especially the kidneys, keeping the balance correct. Blood and plasma always stay slightly alkaline (pH 7.4 with a small variation of 7.35 to 7.45). Normal food intake of either acid or alkaline variety does not change this blood pH. Any variation outside this range is life threatening and an indication of severe malnutrition or dehydration. 

b.The stomach fluid is always acid. Our saliva varies and is usually slightly acidic, but once food goes into the stomach it enters an acid environment (pH 1.5-4.0). This is essential for the first stage of food breakdown and for killing bacteria, viruses and parasites in the food.

c.The rest of the digestive tract varies from alkaline (top of the small intestine) to slightly acid (large intestine) and neutral at the anus. This changes with the digestive juices secreted into the intestinal tract and does not vary that much with the food intake.


From: http://altered-states.net/barry/update178/  This site actually advocates an alkaline diet and sells gadgets to measure drinking water and urine pH. Good diagram, but gadgets not recommended.


3. Effect on bones 

A number of studies have shown no bone calcium depletion due to acidic diets. A recent meta-analysis summed it up as :

“There is no evidence from superior quality balance studies that increasing the diet acid load promotes skeletal bone mineral loss or osteoporosis. Changes of urine calcium do not accurately represent calcium balance. Promotion of the “alkaline diet” to prevent calcium loss is not justified.”

Meta-Analysis of the Effect of the Acid-Ash Hypothesis of Osteoporosis on Calcium Balance

By Tanis R. Fenton, et al J. Bone Miner. Res. 24 (11): 1835–40   2009


A couple of other useful references: 

The Alkaline Diet: Is There Evidence That an Alkaline pH Diet Benefits Health?

By Gerry K. Schwalfenberg,  J Environ Public Health. 2012; Published online 2011 Oct 12. doi:  10.1155/2012/727630

See also: https://authoritynutrition.com/the-alkaline-diet-myth/






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