The 'alkaline' diet has been around for a while, but is it another 'fad' diet or does it have real implications for improved health and weight loss?
What's ‘normal’ alkalinity for the body?
Acidity or alkalinity of a liquid is measured using the pH scale. This scale has a range from a pH of 1 (which is extremely acidic) to a pH of 14 (extremely alkaline). Water has a pH of around 7, which is neutral pH, neither acid nor alkaline. In contrast our stomach acid has an extremely acidic pH of 1-3, essential to help us digest food.
The pH of blood is carefully controlled within a very narrow range of pH 7.35-7.45, which keeps blood slightly alkaline. It’s incredibly important to maintain this tight pH range as millions of cell reactions taking place in our body each day work best in a slightly alkaline environment. Blood pH naturally varies over the course of the day, but will always fall within this range.
To maintain blood pH requires exquisitely sensitive monitoring and adjustment by our body. The key organs adjusting blood pH are the kidneys, which rid the blood of excess acid or alkali into the urine. For this reason the pH of urine can vary much more (usually between a pH of 4.5 to 8). Breathing rate can also be adjusted - without us even realising it - to regulate carbon dioxide levels in our blood which can also adjust pH levels. In addition, our bones can release calcium to help ‘buffer’ an acidic blood, but this is undesirable as long-term bone calcium loss can increase the risk of osteoporosis. Severe kidney or lung disease, or uncontrolled diabetes can cause blood pH to fall outside this range.
The alkaline food theory: What is it?
The alkaline diet is way of eating that recommends that the proportions of foods eaten in the diet should be based on their ability to alter blood acidity or alkalinity. It claims the diet - which advocates eating 70% alkaline-producing foods and 30% acid-producing foods daily - aids weight loss and can help control long-term conditions and diseases like diabetes, arthritis and cancer, as well as slowing the ageing process. In addition ‘Alkaline water’ has been a recent addition to the dietary recommendations, either bought as a drink, or a machine to generate alkalinised water.
Which foods are which?
Foods are classified according to their potential to create acid or alkali when metabolised, and not based on their natural acidity levels at the point of eating.
Scientifically, acid producing foods tend to be rich in protein or phosphorus. Acid-producing foods include meat, poultry, fish, processed foods, dairy products, bread and rice.
In contrast, alkaline-producing foods which have an opposite effect on pH, are those rich in the minerals magnesium, potassium or calcium. Vegetables, fruits, pulses (peas and beans) and potato all have an alkaline potential. Citrus fruits and juices also fall into the alkaline category, despite their acidic taste, due to their potassium content which has an alkaline influence on the body. The mineral content of a daily one-a-day vitamin and mineral supplement also helps boost the alkalinity potential of the blood.
There’s not enough evidence at the moment to say whether a food is either alkaline, or acid, producing, and some foods are ambiguous in their definition. Cheddar cheese, for example, is rich in protein and phosphorus - two dietary components known to be acid-forming in the body. Yet cheese is also a rich source of calcium, which helps contribute to alkalinity levels in the blood.
Our daily food variety, relative portion sizes, activity levels, age and overall health status all have a significant influence on blood pH which can’t be solely accounted for by diet