Bananas with brown spots kill cancer! Eat them!

I read this exciting declaration on Facebook.

According to the post: "Fully ripe bananas with brown patches on their skin produce a substance called tumour necrosis factor, which can eliminate abnormal cells. The darker the patches, the higher the banana's ability to boost your immunity and lower the risk of cancer".

It was posted with the encouragement: "Share with the people you care about".

I didn't share it.

One of the banana posts from Curejoy. ( Supplied: Tanya Ha )

Facebook is full of cures and killers.

Some posts are helpful, such as those warning home renovators to check for asbestos.

But there's also a mountain of posts about a wide and weird range of things that allegedly cause cancer: hand soap, bras, dairy milk, almond milk, deodorant, mobile phones, drinking cold water after a meal, and even chemotherapy.

I went on a banana fact-checking mission to find out who made the original post and what it was based on.

The real banana facts

Let's start with the science.

What is tumour necrosis factor?

It's a protein that causes inflammation as part of your body's natural defences. Macrophages, a type of white blood cell, make it when a threat is detected.

Why would a substance made by blood cells be in a banana?

Some versions of the banana meme refer to a Japanese study.

It was a mouse study, not a human trial — and the mice didn't eat bananas. The researchers pulverised slices of very ripe banana in water, then injected the mice with a filtered extract. The immune systems of the mice produced tumour necrosis factor as part of the normal immune response to dealing with something that shouldn't be there.

The scientists made no claim that the bananas produced the factor, or that they'd found a cancer cure. At best, the meme is gross misrepresentation of clinically insignificant research.

Who made the claim?

The banana meme was posted on the Facebook page of Ayurveda by Curejoy, self-described as "Expert advice on Cure, Fitness and Beauty."

The page has nearly 10 million followers, and cross-promotes the magazine-style website CureJoy.com.

The website's "about" page doesn't name the people behind it, but it does invite advertisers. If you click on the media kit link, you'll see this:

This is the information presented to marketers in the Curejoy media kit. ( Supplied: Tanya Ha )

My guess is that the website's modus operandi is simply to attract your eyeballs with appealing content, and sell advertising to companies who want your eyeballs.

So, what's the harm?

The trouble is, this all adds to the noise that vulnerable people with serious illnesses are dealing with. Noise that's amplified by empowered friends. Friends who were impressed by a YouTube documentary or a miracle food book; or who have "done their own research" with the help of Doctor Google.

Cancer and "wellness" got very personal for me over the past 10 years. Three of my best friends have survived cancer. And my much loved brother-in-law Graham died from lung cancer in 2008.

Then in 2012, my adored sister found a lump in her breast.

Tanya Ha (right) helped her sister navigate through the false health claims that surround cancer. ( Supplied: Tanya Ha )

I knew what was coming. My sister was about to get a barrage of well-meaning but poorly-informed advice from friends — sometimes gentle, sometimes dogmatic, and often confusing, contradictory and distressing. My protective instinct kicked in.

It was then that I really came to appreciate the BS-detection skills you learn as a science journalist.

I went to my sister's medical appointments, and later explained anything she hadn't understood — like what sentinel lymph nodes are, and why they're biopsied.

And I was her gatekeeper. With her and her husband's blessing, we told everyone to channel communication through me. I would call them, send group text messages and post updates on Facebook after surgery and doctor's appointments. They could pass on health information through me.

We asked our friends to give her the space and peace she needed to concentrate her physical and emotional energy on treatment, recovery and keeping her three children happy.

A few friends were insistent on recommending various treatments, or evil chemicals to avoid, so I went on many fact-checking missions, talking to doctors and scientists, researching the evidence and relaying what I found to my sister.

By and large, it worked. But one incident made me furious.

A while after surgery and radiotherapy, my sister saw a "dietitian"* for advice on what to eat to help with her recovery. She left in tears, having paid $180 to be told that she must have given herself cancer by having a diet that's too acidic.

Please share with care

Cancer is a health challenge, but cancer survivorship is a mental health challenge.

How anyone can take money from a scared, trusting young woman and tell her such anxiety-inducing bollocks is beyond me! And yet they do.

It's true that cancer cells can't live in an overly alkaline environment, but neither can any of your cells. Stomach acid is far more acidic than most of the food it digests. And because your enzymes function in a narrow pH range, your body has complex and multiple systems to keep it from changing. Acidic diets do not cause your blood to become too acidic.

Every Facebook post promoting alkaline water makes me think of my sister. I wonder if she's reading the same post, feeling a stab of fear, guilt, doubt or anxiety.

Sorry, this audio has expired Facts, fear and Facebook

Some things, like bacteria and computer viruses, are dangerously shared.

Wellness warriors Jess Ainscough and Belle Gibson shared their diets and cancer cures with thousands of followers on social media as alternatives to conventional treatment.

Jess Ainscough has since died from cancer; Belle Gibson never had cancer in the first place and is facing fraud and contempt charges. They may have influenced people making life-and-death decisions about their own cancer treatment.

Humans have hearts as well as heads. The real power of Facebook lies not in facts but in feelings. The posts that make us laugh, cry, fume or feel scared are the most liked and shared.

Truth matters.

The next time you're called upon to "share if you care" — please, instead, share with care.

If you really do care about your friends and family, you can take five minutes to fact check first.

* Note: In Australia, anyone can legally call themselves a nutritionist or dietitian, no matter their level of training, much to the frustration of evidence-based, qualified and trained nutritionists and dietitians.

Tanya Ha is director of engagement at Science in Public, a member of the executive committee and board of Science and Technology Australia, and was once a reporter on ABC TV's Catalyst.