Fad diets are nothing new. But one you may have spotted doing the rounds on your social media feeds claims to do everything from slow down ageing to cure cancer.
Yes, it's the alkaline diet, and its fans range from chefs to alternative therapists to a whole host of A-listers (Elle Macpherson, Gwyneth Paltrow and Kate Hudson are all reported to be devotees).
There are a number of doctors on the bandwagon, too. Dr Stephan Domenig, who wrote The Alkaline Cure (2014), and Dr Robert O. Young, author of The pH Miracle (2002), have been vocal about the diet as a pathway to tip-top health and less disease. (That said, Young has since faced jail time for practising medicine without a licence, and for advising a cancer patient to stop chemotherapy.)
So is there anything good about this way of eating? Can what we eat really 'alkalinise' our blood? Or is it just a gimmick? We look at the research and talk to experts to find out.
Meat, fish, poultry, eggs, grains and dairy are off the menu on the alkaline diet.
What is the alkaline diet?
The alkaline diet is an eating plan that supposedly works by balancing the pH of the blood. It splits foods into two categories – acid-producing foods and alkaline-producing foods. It then asks that you cut out all acidic foods from your diet to achieve optimal health. But in practice, say experts, this is very hard to do.
"It's essentially a fad diet that cuts out three main food groups – meat, fish, poultry and eggs; grains; and dairy," says Melanie McGrice, an accredited practising dietitian and spokesperson for the Dietitians Association of Australia (DAA).
"The diet allows some alternatives such as nuts and seeds, but it's essentially a very restrictive grain-free vegan diet."
But can the foods we eat actually alter how acidic or alkaline our bodies are? Can we tinker with the pH of our blood by what we put into our mouths?
There are no foods that you eat that can change the pH of your bloodMelanie McGrice, Dietitians Association of Australia
Absolutely not, according to McGrice. "There are no foods that you eat that can change the pH of your blood," she says. "If foods did this to any extent and your pH fell outside of the tightly controlled normal range, your cells would stop working and you would die very quickly if left untreated."
She adds that the body already has its own amazing mechanisms for maintaining pH balance.
"Our renal and respiratory systems eliminate waste through urine, saliva, sweat and gases via our breath," says McGrice. "So we don't necessarily need to be removing whole food groups to maintain our pH balance. Our body does it for us naturally."
What does the alkaline diet claim to do?
The marketing behind the alkaline diet is varied, says McGrice.
"Proponents claim that the diet can help you lose weight, reduce inflammation, optimise fertility, decrease high blood pressure, cure depression, protect bone health and everything in between – but there's very little evidence for the claims made," she says.
Most infamously, though, it's been marketed as a way to prevent or cure cancer, which is of particular concern to doctors and nutrition experts. The claims come from studies suggesting that cancer cells thrive in acidic or low-pH environments. But the studies were done on cancer cells in a petri dish, not in a human body.
There is currently no good evidence that [the alkaline diet] can be used to prevent or treat diseases such as cancerClare Hughes, nutrition program manager at Cancer Council NSW
"Well-designed studies on alkaline diets in people are lacking, and there is currently no good evidence that they can be used to prevent or treat diseases such as cancer," says Clare Hughes, nutrition program manager at Cancer Council NSW.
"The things we eat and drink can have a profound effect on our risk of getting cancer, but the acidity or alkalinity of foods is not something to be concerned about."
If you're undergoing chemotherapy, following the alkaline diet can exacerbate your risk of malnutrition.
Can the alkaline diet be dangerous to cancer patients?
Hughes says many people going through cancer treatment understandably look for things they can do to give themselves the best chance of curing the disease – including changing their diet.
"A well-meaning friend or family member may recommend a particular diet they've heard about or they may come across so-called 'anti-cancer' diets on the internet and try these things because of testimonials from people who claim to have 'beaten' cancer using diet," she adds.
"These 'anti-cancer diets' often include scientific rationale that make them appear plausible, but in reality there's little evidence that any diet or eating pattern can treat or cure the disease.
'Anti-cancer diets' often include scientific rationale that make them appear plausible, but there's little evidence that diet or eating pattern can treat or cure the diseaseMelanie McGrice, Dietitians Association of Australia
"It is particularly concerning when patients choose to forgo cancer treatment with the belief that alternative treatments such as diet will cure them."
McGrice adds that very low-calorie diets that cut out food groups can pose further risks to cancer patients, at a time when they need nutrition and calories more than ever.
"Oncology patients can develop a type of cancer malnutrition, because it is thought some cancer cells burn calories so quickly," she explains.
"Treatments like chemotherapy or radiotherapy can have an impact on taste and appetite, which may also cause weight loss – so if you add in a diet like the alkaline diet, it can really exacerbate your risk of malnutrition."
Does the alkaline diet have any benefits?
So is the alkaline diet all bad? Not exactly – it is, after all, pushing the good stuff in a world where over-processed diets and health issues are rife. In Australia alone, research shows that only one in 20 adults (5.1%) eat their recommended daily allowance of fruit and vegetables, and that a whopping 42% of our energy intake comes from ultra-processed foods.
"The alkaline diet does encourage the consumption of fruit and vegetables and most people aren't eating enough of those – so that's definitely a benefit," says McGrice.
"It may also help you lose weight, but that's because it's low in calories – it has nothing to do with 'alkalinising' your body. Because it cuts out so many food groups, it's still a fad diet."
The alkaline diet does encourage the consumption of fruit and vegetables.
Does the alkaline diet have any downsides?
In a word, yes. Staying on it long-term could put your health at risk in ways you might not have expected.
"Cutting out so many food groups may impact your gut microbiome," McGrice says. "Emerging research shows that micro-organisms in our guts have an impact on a whole range of health conditions, from mental health to putting us at risk of certain chronic diseases.
"And while there are some claims that the alkaline diet can prevent or cure depression, the fact that it's very low in B vitamins means there's a risk it could potentially cause it, too.
"Plus, being so limited in calories, the alkaline diet could also set off someone who was at risk of an eating disorder."
Cutting out so many food groups may impact your gut microbiomeMelanie McGrice, Dietitians Association of Australia
There's also no evidence that the alkaline diet can protect bone health – as its proponents often claim.
"Proponents of the alkaline diet claim that a high dietary acid load decreases bone-making activity, but there is no evidence of this theory," says McGrice.
One frequently cited study did find higher calcium levels in post-menopausal women who were given alkaline potassium bicarbonate supplements, but the study has significant limitations.
"Furthermore, cutting out dairy makes it more difficult to meet calcium requirements, which puts your bones at risk of osteoporosis," says McGrice. "I have so many clients say, 'Oh, I had my calcium levels checked in a blood test and they're fine', but the truth is, your levels will always be fine in a blood test unless you have an underlying health condition.
"Your body works to remove calcium out of your bones to keep the levels of calcium in your blood adequate. So you really need something like a DEXA scan to know what your bone density is like."
Still want to try it?
Perhaps you're keen to try the alkaline diet anyway – or maybe you want to supplement your diet with expensive alkaline waters and pH drops. Should you do it?
"If you can afford to buy it, alkaline water is probably not going to hurt you unless you have a kidney problem, but I'd rather see people spend their money on things that are evidence-based," says McGrice.
"If you're going to try the diet despite there being no evidence behind it, you should not do it long-term, and you shouldn't undertake it without seeing a dietitian.
"If you're cutting out so many core food groups, you really need to be replacing them all [in other ways] to make sure you're meeting all your nutritional requirements, which is quite challenging to do."
And if you have cancer, get advice from a dietitian at the hospital where you're having treatment before making any dietary changes, adds Clare Hughes.
"The dietitian will be able to provide the best advice based on your type of cancer and treatment regime," she says. "Because some people lose weight or become malnourished during cancer treatment, you may be better off focusing on getting enough calories."