Nothing gives a diet regimen a higher profile than the endorsement of super-svelte Hollywood celebrities.

The latest weight-loss craze, the acid/alkaline diet, claims to have the backing of Gwyneth Paltrow and Kate Moss.

The diet is based on the idea that eating certain foods, such as meat and dairy, can increase the body’s acid levels to dangerously high readings, dubbed ‘hyperacidity’.

Supporters of this theory not only believe this can build fat, but longer term it can lead to an increased risk of cancer and osteoporosis.

The diet is based on the theories of U.S. naturopath Robert Young, who has written a series of books promoting the idea that hyperacidity is a common health problem and can be fixed with the right diet.

He advocates living almost entirely on foods that will supposedly make the body’s internal environment less acidic, such as vegetables, fruit, beans and pulses.

The diet also involves cutting out foods that make the body more acidic, such as meat, dairy, sugar, white flour and pasta.

Devotees undergo regular blood or urine checks (the diet has spawned DIY tests available on the internet and costing £13 for 100 urine testing strips) to make sure acid levels are controlled, and to measure the balance between acid and alkali in their blood.

So should we all start measuring our acid levels and ditching bacon for breakfast?

Though there is science to support the reasoning behind this regimen — especially when it comes to the link between diet and brittle bones — experts caution the diet is a mix of fact and fiction.

It is true that the body does contain natural acids and alkalis, and that a balance of these is crucial to create the right conditions in which all the body’s hormones and enzymes can function properly.

‘However, you can’t just eat a bit more of a particular food and hope it will reduce your acidity,’ says Catherine Collins, chief dietitian at St George’s Hospital, London.

She adds that the link to cancer and weight-loss is unproven.

Furthermore, urine tests to see if you need to alter your eating habits could be a waste of time.

That is because urine is used by the kidneys to transport excess acids or alkalis out of the body, so a high reading of either simply means the body is doing what it is supposed to — flushing out the chemicals it does not need.

In fact, the body has a sensitive and sophisticated method of keeping acid and alkali levels in check.

Acid levels are measured using a scale called the pH balance. The letters stand for ‘power of hydrogen’ because it measures the concentration of hydrogen, and the scale goes from one to 14, with one being acid and 14 alkali.

In the blood, acids and alkalis need to be balanced for cells and tissues to function properly, so the pH needs to remain within an extremely narrow range of 7.35 to 7.45, which is slightly alkaline.

‘The body has become clever at maintaining blood pH within tight limits,’ says Professor Susan Lanham-New, head of nutritional sciences at the University of Surrey.

The lungs and kidneys are two of the main methods for controlling this acid/alkali balance.

When we breathe out, our lungs expel carbon dioxide, one of the body’s main sources of alkaline material. If the blood starts to become slightly too acidic, breathing automatically slows down to retain some of that carbon dioxide and restore the pH balance.

The kidneys monitor the body’s acid and alkaline levels round the clock and flush out any excess through our urine.

In fact, major fluctuations in pH balance occur only when there is a serious illness, such as kidney failure, that has been brought on by chronic health problems such as high blood pressure or diabetes.

However, the principles of the diet may have some foundation in science.

According to Professor Lanham-New, research has shown certain foods do produce acid or alkali when they are digested by the body.

This means the body must then restore the pH balance back to normal.

The foods that produce acids are meats, hard cheese, bread and pasta, while the foods that create alkali are fruit and vegetables (surprisingly, even citrus fruits have an alkaline effect on the body).

While this doesn’t mean any foods should be avoided, as recommended in the hyperacidity diet, it does mean that balance in the diet is crucial, otherwise our bones could pay the price, says Professor Lanham-New.

A large amount of meat creates acid and so the body needs to create alkali to restore the balance. Recent research has shown one source of alkali in the body is alkali salts found in the bones.

Specialised cells ‘munch away at our bones’, says Professor Lanham-New, to remove these alkali compounds, but this leaves our bones weaker.

One study that placed men on a diet of acid-forming foods found their rate of bone loss increased by 19 per cent compared to those on a diet rich in alkali foods.

However, Professor Lanham-New does not advocate the strict regimen of the hyperacidity diet. Instead, it’s important to remember that fruit and veg should not be an after-thought in our diets.

‘The advice of our parents’ and grandparents’ generation of meat and two veg is one we should all try to follow,’ she says.