Image copyright Getty Images Image caption Patriots' quarterback Tom Brady advocates for an "alkaline" diet to adjust blood's PH levels

From coffee enemas to alkaline diets, celebrities like Gwyneth Paltrow and Tom Brady are using their star power to sell dubious health treatments to the adoring masses. What's a scientist to do?

New England Patriots quarterback Tom Brady on Sunday hopes to break the record as the oldest quarterback to win the Super Bowl.

Brady, 40, is still at the top of his game. This season he led the Patriots to a spot in the championship game while nursing a hand injury.

His secret? You'll have to buy his latest diet book, The TB12 Method, if you want to find out.

Brady advocates in the book that people eschew "nightshade" vegetables like aubergines (eggplants) and tomatoes, in favour of "alkalizing" and "anti-inflammatory" foods to increase the blood's pH and speed up muscle recovery.

But just because Brady may be the GOAT (greatest of all time) on the field, does not mean he is the greatest scientist of all time, says Tim Caulfield, a Canadian health policymaker and pseudoscience critic.

"There is almost no evidence to support this monk-like approach to eating," Caulfield wrote in an article .

"Brady's approach seems to be loosely based on the alkaline diet, which is the idea that you can control the pH of your blood through the food you eat. (Spoiler: you can't.) As noted in a 2016 systematic review of the relevant evidence, 'there is almost no actual research' to support the ideas behind the alkaline diet."

Caulfield, the government-appointed Canada Research Chair in health law and policy and the author of the book, Is Gwyneth Paltrow Wrong About Everything?, is part of a growing segment of scientists loudly critiquing celebrity health-guru culture online.

"Quackery," Caulfield says, has always been around. From sideshow elixirs to bloodletting, snake oils have always co-existed with evidence-based medicine.

"But what I think has happened right now has a bit of a different flavour to it."

As people become more science-literate, pseudoscience has adopted scientific language to justify itself, Caulfield says.

For instance, in a recent edition of Gwyneth Paltrow's newsletter, Goop, Paltrow praises an alternative treatment to Lyme disease that uses "quantum science to analyze varied aspects of a patient's health, including energetic aspects".

While one would be hard pressed to find an actual quantum physicist who believes that subatomic particles can treat a bacterial infection, Caulfield says that alluding to something as complex as quantum science can be powerfully persuasive.

"Because it is so complicated, it looks like it could explain anything," he says.

Another factor in the rise of quackery is the growing power of celebrity, he points out. With huge social media presences and the ability to appear on multiple platforms at once, celebrities are able to spread ideas broadly - and quickly.

Studies have shown how celebrity promotion can influence people's medical choices for good and bad. A 2017 study published in Health Service Research found that the number of women opting for a risk-reducing mastectomy increased after Angelina Jolie wrote an op-ed about her own procedure. Another study, published in 2017 in Prevention Science, found that sales for oral HIV testing kits went up after Charlie Sheen announced he was sick.

"Celebrities can keep ideas alive, they allow ideas to gain traction," Caulfield says.

Image copyright Matt Barnes / Peacock Alley Entertainment Image caption Tim Caulfield says we have to do more to fight pseudoscience online

People seem especially susceptible to pseudoscience when science fails to provide an easy answer, he says. Science does not promise certainty - only probability.

"Purveyors of these unproven treatments are offering simple answers, and they're offering comprehensive answers - 'This will fix you'," Caulfield says.

So what's an evidence-loving scientist to do? Ask Dr Jen Gunter, a California-based gynaecologist who uses her popular blog and active Twitter account to take on everyone from Gwyneth Paltrow to Donald Trump.

In posts on her own blog and in columns for the Guardian and the New York Times, Gunter implores women to ignore the latest celebrity-backed health trend.

"Coffee enemas and colonics offer no health benefit," she wrote after a Goop newsletter suggested one might help women rid their colons of "toxins" leftover from a cleanse.

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"The biology used to support these therapies is unsound and there can be very real complications. Keep the coffee out of your rectum and in your cup. It is only meant to access your colon from the top."

Gunter's profanity-laden wit has turned her into a kind of Amy Schumer-with-a-medical-degree, and has endeared her to some 67,000 followers on Twitter.

"I think the only way you can beat celebrity is with some degree of celebrity," she says, which means if scientists want to go after celebrity gurus like Paltrow and Brady, they will need to both entertain and inform.

Gunter's frequent attacks on Goop's lack of scientific underpinnings have not endeared her to Paltrow, who published a letter calling out Gunter by name.

"Since her first post, she has been taking advantage of the attention and issuing attacks to build her personal platform - ridiculing the women who might read our site in the process," wrote Goop's "contributing doctors".

In subsequent letters to the media, Goop was quick to point out they always carry a disclaimer that their articles are not "a substitute for professional medical advice, diagnosis, or treatment, and should never be relied upon for specific medical advice".

Gunter is not the only one who has earned the ire of a health guru. Joe Schwarcz, who holds a PhD in chemistry and is the director for McGill University's Office for Science and Society, has gotten into heated arguments with alternative food blogger Vani Hari, known as "The Food Babe".

She advocates against all synthetic ingredients, often touting the motto, "if you can't pronounce it, it must be harmful".

Hari's attitude, Schwarcz says, is symptomatic of a misconception that he has been fighting for nearly 40 years - the association of natural with beneficial and synthetic with harmful.

"We spend most of our life trying to overcome the ravages of nature," he says, rattling off deadly substances like botulism, snake poison and malaria - all which occur in nature.

After Schwarcz was quoted in a New York Times article she felt was biased against her, Hari slammed Schwarcz and accused him of being funded by chemical companies.

"Based on his advocacy, one could say Dr Schwarcz hasn't met a chemical he doesn't like," she wrote on her own website.

Schwarcz denies receiving funding from the chemical industry to attack her work.

In 2005 he received funding from the Council of Biotechnology Information, which includes chemical-industry firms such as Monsanto and Dow, to pay for research interns.

Image copyright Getty Images Image caption Gwyneth Paltrow (far right) during a panel of In Goop Health, her alternative health conference

Vocal critics like Caulfield, Schwarcz and Gunter have also gained a level of popularity themselves.

Caulfield has published multiple books and hosts a television show. Schwarz hosts a science radio programme and is frequently interviewed by the media. Gunter has parlayed her blog into a New York Times column and is working on a book about women's health.

But Gunter says there is a world of difference between advocating for listening to medical experts and advocating for a person to delay cancer treatment to, say, start a course of "vitamin supplement therapy".

"Those are dangerous messages," Gunter says. "It pushes everybody a step back if people actually believe that."