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The superfood studies suggest could HALVE your cancer risk - but experts say there's more to it
Over the years, fringe scientists have claimed that various compounds in everyday foods that can help to prevent cancer.
From phytochemicals found in fruit to omega-3's found in walnuts, popular ideas about foods that fight cancer have come and gone.
Now, the spotlight appears to be on an unlikely vegetable: mushrooms.
An intriguing tweet posted by nutrition coach Lori Shemek shared details of a study involving nearly 20,000 people that appeared to suggest eating just one mushroom per day could cut your risk developing all cancers nearly in half.
'Cancer absolutely hates mushrooms,' Shemek, who is not a medical doctor, wrote.
The claim appears farfetched — but recent studies do appear to suggest that some types of the edible fungi could be useful in fighting cancer cells. So should we all up our mushroom content?
Shiitake and turkey tail mushrooms are commonly promoted for their potential in preventing cancer. Neither have been proved effective by US scientists or authorities.
About 20 million cases of cancer were diagnosed in 2022, but that number is projected to balloon to more than 35 million cases by 2050, according to the American Cancer Society.
Mushrooms have been used by Asian doctors in the hope of treating a number of health problems for centuries. Extracts from turkey tail mushroom and shiitake mushrooms are currently approved to treat cancer in Japan and China.
American doctors became attuned to the trend around the dawn of the 21st century, while a series of studies have thrust the vegetables into the spotlight in recent years.
One is the 2021 review referred to by nutrition coach Lori Shemek, conducted by experts at Penn State University.
The scientists reviewed 19 previous studies of many mushroom varieties and found eating 18 grams of any mushroom daily could reduce your risk for developing all cancers by 45 percent.
That's about one standard sized white button mushroom daily.
However, of the 19 studies they analyzed, only 11 controlled for other factors that could've influenced cancer risk - like exercise, body weight or other dietary choices.
And it is likely that those who eat diets high in mushrooms are also likely to eat other vegetables and fruit, as well as exercise, meaning their low cancer risk may come from other elements of their lifestyle.
Of the 270 potentially useful mushrooms, only 32 have demonstrated scientific benefit in the lab, the bulk of evidence shows.
And of those 32, only 11 have been tested in people, according to a 2022 review from Indian and Belgian scientists.
This review concluded that five kinds of mushrooms are the most promising: shiitake, turkey tail, reishi, white cap and maitake.
It is thought that the vitamins and antioxidants found in these five mushrooms could help protect against cancer by muting the effect of free radicals — molecules that cause damage to our DNA and cells.
These include vitamins B, D, selenium and niacin, as well as two little-known compounds called ergothioneine and lentinan.
For instance, one 2011 study suggested taking reishi extract for a year could reduce people's risk of developing colon cancer.
The researchers did this by studying 225 Japanese people with abnormal cells in their colon, called polyps. Polyps are abnormal cells that turn into cancerous tumors in roughly 10 percent of cases.
At the end of the year, people who took reishi extract had fewer polyps overall than the people who didn't.
This suggested that the extract might be able to aid in preventing colon cancer, the US National Cancer Institute wrote.
However, it was done in a small group of people and hasn't been tested again in this manner. It's also unclear if the researchers controlled for other factors that could've influenced their polyps, like genetics, diet or exercise routines.
The evidence for reishi overall is scant, which explains why no US regulatory agencies have approved the mushroom for at treatment or prevention for any medical condition, according to NCI.
Much of the interest in turkey tail mushroom is rooted in the effects of a compound that can be distilled from the fungus called polysaccharide K (PSK).
Japanese scientists suggest PSK could help the body produce a greater number of the proteins that fight back against harmful invaders like viruses or cancer.
When taken alongside other treatments, like surgery or chemotherapy, people who took PSK supplements in roughly 20 different studies were less likely to have recurrent stomach, colorectal and lung cancers than those who took traditional treatments alone, according to the NCI.
But these studies only included small groups of people, were mainly performed in Asia, showed minimal benefit, and most did not control for other, potentially beneficial influences.
All told, this study and others haven't provided overwhelming evidence that mushrooms can treat or protect against cancer, Dr Liz O'Riordan, a breast cancer surgeon, told the Irish Examiner.
'We do know that being a healthy weight and that exercising can halve your risk of most common cancers. However, there is no evidence to say that mushrooms will reduce your risk or eating soy will reduce your risk of getting cancer,' Dr O'Riordan said.
It's always a good thing to eat a more nutrition diet, but it's unlikely, based on the current evidence, that mushrooms are a magic bullet, she suggested.
So adding mushrooms to your diet if you're interested in getting more nutrients isn't a bad idea, but US authorities caution that you shouldn't rely on it.
'Patients will read these blogs and podcasts and spend money on supplements and avoid sugar or buy Turkey Tail mushrooms in the belief that one person has said it will cure them or it will reduce the risk,' Dr O'Riordan said, 'and no one backs up the science.'