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Behind the science: Alkaline diets

What are alkaline diets and is there anything in it for us? HFG senior nutritionist Rose Carr takes a closer look.

According to proponents of alkaline diets, if we eat mainly alkaline foods we can improve the pH in our bodies and thus improve our health. They’re also promoted as weight-loss diets.

What’s the theory behind alkaline diets?

The pH scale is a measure of acidity and alkalinity. Acids have a pH less than 7; a pH of 7 is neutral; and a pH greater than 7 is alkali (also called base, as in the acid-base balance). The normal pH range for our blood is 7.35 to 7.45, so it is slightly alkaline. The theory behind the alkaline diet is that the foods we eat should reflect the alkalinity of our blood as eating too many acid-producing foods makes it more difficult for our bodies to maintain this balance.

To check the results of dietary changes, people following these diets use litmus strips to test the pH of their urine. This is because our kidneys help maintain the acid-base balance in our bodies by regulating the disposal of hydrogen ions (which are what is actually being measured when we talk of acidity and alkalinity).

What’s in an alkaline diet?

The alkaline diet comes in different forms and is sometimes called the acid alkaline diet. Generally, the diets advise that from 70 to 80 per cent of our foods need to be alkaline and to achieve this we’re told to limit or eliminate acid-forming foods (see below). Drinks including tea, coffee, alcohol, sugary and carbonated drinks are often on the banned list as well, whether or not they are acid-forming.

Acid and alkali-forming foods

Once digested and metabolised, most foods release either acid or alkaline by-products into the circulation:

  • Alkali-forming foods include fresh vegetables (including starchy vegetables) and fruit.
  • Acid-forming foods include fish, meat, poultry, eggs, shellfish, cheese, bread, cereals and grains.
  • Legumes are mildly acid-forming.

Many people assume tomatoes and lemons are acid-forming but as with most vegetables and fruit, they release more alkaline by-products once they’re fully metabolised.

Just because foods are acid-forming doesn’t make them unhealthy! We need to look at the big picture of our overall diet.

Does it work for weight-loss?

It’s likely that if you follow this diet you will lose weight simply because it’s restrictive, so you’re likely to consume fewer kilojoules. If you don’t consume fewer kilojoules, it’s not likely to result in weight-loss.

Is there any scientific evidence about this diet?

There is some evidence that a more alkaline diet is beneficial, although not to the degree that some popular diets promote.

A typical Western diet produces more acid than alkali, so overall it’s slightly acidic. Our kidneys, lungs and buffering systems take care of this for us, operating together to keep our blood pH tightly controlled.

However, some researchers now believe that this dietary acid load over a long period, alongside a slow decline in kidney function as we age, results in a chronic low-grade metabolic acidosis (too much acid in the bodily fluids) which over time can be harmful to our health.

Bone health is also thought to suffer with a high-acid diet because when we have excess acid in the body, calcium salts are released from our bones, used to buffer excess acid, and calcium is then lost from the body in urine.

There is little evidence at this stage for other health benefits, so further claims by those promoting alkaline diets could be described as hyperbole. There is, however, great interest in possible health outcomes from a low acid load diet and the research continues.

Are there other diets that have similar benefits?

In general, a diet high in animal protein will have a high acid load. However, it has been shown that a low acid load can also be achieved by replacing nutrient-poor, energy- dense foods with a higher intake of vegetables and fruit without any great restriction on protein. Increasing the amount of vegetables and fruit in our diets, (which is also how we reduce the acid load), will improve the ratio of potassium to sodium which has been shown to lower blood pressure and improve heart health.

Bottom line

At Healthy Food Guide, we’re not big fans of fad diets. We believe in healthy dietary patterns and making small but significant changes to improve our diets as needed. The alkaline diets often come with long lists grading the acidity or alkalinity of many different foods. It’s worth noting there are discrepancies between different food lists that have been published. This puts the focus on the small picture rather than the big picture. And it doesn’t sound like much fun, either!

We recommend going back to the big picture. The acid-alkaline balance is just one more example of why increasing the proportion of vegetables and fruit in our diets is good for us. Just keep in mind the ideal plate — with half holding our portions of protein and carbohydrates, and the other half piled with low-energy vegetables — and we’ll be on the right track.

Did you know?

The pH in our bodies varies:

  • While our blood is slightly alkaline, the pH in our stomach ranges from 1.35 to 3.5. This acidic environment helps digestion as well as protecting us from microbes.
  • Our skin is also acidic (pH 4-6.5) to provide a protective barrier to the environment against microbial overgrowth.
  • Our urine varies from acid to alkaline depending on what needs to be excreted to maintain our inner balance.
First published: Mar 2015



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