Maintenance of the acid-base homeostasis is a vital function of any living organism. The blood’s acid-base balance is precisely controlled and even a minor deviation from the normal range, can predispose one to disease. When severely deranged, the deviation can threaten life itself. The body uses different mechanisms to control the blood’s acid-base balance. Our lungs and kidneys play a vital role. Nutrition too has long been known to strongly influence this balance. All foods are “burned” in the body — more commonly called “digested” — leaving an ash as a result. This food ash can be neutral, acidic or alkaline, depending largely on the mineral composition of the food ingested.
Foods that leave behind acidic residues are known as acid-forming foods. A protein–rich diet, such as consumption of eggs, meat, poultry, legumes, pulses and nuts produce acidic residues when oxidised for energy.
In contrast, fruits and vegetables leave an alkaline or basic ash. They contain magnesium, calcium, and potassium salts of organic acids, which yield an alkaline residue when oxidised. Even though fruits taste sour or acidic, their pH is alkaline with respect to the body and hence are classified as alkaline foods.
Excessive intake of acid-forming foods can lead to metabolic acidosis due to depletion of the alkali reserve or reduction in the reserve supply of fixed bases in the blood and the tissues of the body. Acidosis occurs when blood pH falls below 7.35. Symptoms include nausea, generalised weakness, depression of central nervous system through decreased nerve transmission. Acidosis produces deep respiration as a compensatory phenomenon in order to expel more carbon dioxide from the body. Eventually, it may lead to disorientation, loss of consciousness, coma and even death. Excessively acidic diets can increase risk of osteoporosis, autoimmune conditions such as rheumatoid arthritis and chronic inflammation.
Alkalosis is a condition when acid-base disturbance is caused by an elevation in plasma bicarbonate (HCO3) concentration and the blood pH rises above 7.45 (alkaline). Its symptoms include confusion, hand tremor, light-headedness, muscle twitching, nausea, numbness or tingling in the face or extremities, prolonged muscle spasms (tetany), convulsions and if severe, loss of consciousness and death. Severe alkalosis depresses respiration.
An optimum ratio between acid and alkaline foods in the diet is important. When an ideal ratio is maintained, the body develops strong immunity. In most disease states, catabolic state or fasting, the patient develops acidosis. Increasing intake of alkaline foods accelerates the healing of disease. The higher the ratio of alkaline elements in the diet, the faster will be the recovery. Alkalis neutralise the acids. Therefore in the treatment of most diseases it is important that the patient’s diet includes plenty of alkaline-ash foods to offset the effects of acid-forming foods and leave a safe margin of alkalinity.
The greater the quantity of organic and sulfuric acids produced from metabolism of animal foods, and lower the amounts of potassium salts to metabolise to bicarbonate, which come mainly from fruits and vegetables, the greater the production rate of acid. Metabolic acidosis promotes muscle wasting and the net acid load from diets rich in acid-forming foods may contribute to a reduction in lean tissue mass in older adults. A 2008 study concluded that higher intake of foods rich in potassium, such as fruit and vegetables, may favour the preservation of muscle mass in older men and women.
The best guide to maintaining a good balance on a daily basis would be to draw from the food groups (see box) for healthy eating. Aim to achieve at least 5-9 servings ( 1 serving = ½ cup) of fruits and vegetables daily along-with whole-grains, modest intake of low fat dairy, pulses, animal foods and nuts and limit intake of salt, sugar, fat and alcohol.