Social media ‘experts’ and even doctors spread misinformation about health and fitness

With a wealth of information about nutrition and fitness at our fingertips, people think they are getting good advice but even doctors can peddle myths so fitness fans have to be smarter about where they're getting their information from.

Trainer measuring body fat percentage. Getty Images/Tetra images

You’ve decided to get in shape but you’re not sure how best to start. So what do you do: find out the latest scientific thinking or go with the current buzz on social media?

As this newspaper has reported, there's growing concern among doctors that all too many people are opting for the latter, with potentially dangerous consequences.

From crazy diets to dangerous gym routines, the web is awash with pseudo-experts offering advice that’s at best untested and possibly lethal. No wonder doctors want us to check in with them first.

But here’s the thing, when it comes to diet and fitness advice, they, too, may be peddling nonsense.

More than perhaps any other area of modern medicine, nutrition and exercise has repeatedly fallen prey to unproven claims, dodgy practices and pure myth.

Go in to see your doctor for a health check, and you’ll have your weight, height and a few other measures checked and compared against internationally recognised criteria.

So, for example, if your Body Mass Index – that is, your weight in kilos divided by the square of your height in metres - is more than 25, your doctor will tell you you’re overweight. Bad news, right? Certainly for your health insurance premiums, but for you perhaps not so much.

Introduced as a scientific-sounding measure of obesity in the 1970s, BMI is increasingly regarded with suspicion by obesity specialists as evidence mounts that it’s not fit for purpose.

Since the mid-1990s, studies have found that people with BMIs between 25 and 30 – the cut-off for being classed as obese - may have better life expectancy than those in the “normal” range.

Earlier this year, compelling support for this paradox emerged from a study by scientists in the US who compared the BMIs of more than 40,000 people with health measures such as their cholesterol levels and insulin resistance.

The researchers found that nearly half of overweight people, and even 1 in 6 of the very obese, had perfectly good indicators.

In contrast, almost a third of those with “healthy” BMIs proved to be anything but by these measures.

The unreliability of BMI is prompting specialists to turn to a far simpler measure of obesity: waist circumference. This reflects the level of fat around the abdomen, which has been shown to be particularly unhealthy.

Current evidence suggests that anything more than 94cm for men and 80cm for women is good evidence that you’re unhealthily overweight, while anything more than 102cm and 88cm implies obesity.

Yet many family doctors still rely on BMI to assess obesity risk, leading to misleading conclusions about a patient’s health.

Those told they’re carrying too much weight may then be given nutritional advice that’s not merely out of date, but based on myth.

When it comes to diets, perhaps the most common myth is that “a calorie is just a calorie” – implying it doesn’t matter what form your calories come in, they all affect your weight in the same way.

The calorie content of food reflects the energy locked up in its chemical bonds. As such, everything we eat contains calories – including “zero-cal” sweeteners. The difference is we can’t digest them, and so their calories aren’t available to us.

It’s the same with other foods, especially those high in fibre: for every 100 calories-worth of almonds you eat, for example, you access only 76 calories.

In short, living organisms are not like engines: they respond to the same amount of “fuel” in different ways, and the simple act of eating food is just the start of a process far more sophisticated than much of the advice we’re given about it.

So, for example, we’re routinely warned about “sugar” but rarely told about that while healthier-sounding fruit sugar, fructose, has the same calorie content as glucose, it’s suspected of triggering cravings that make it a bigger obesity risk.

Many family doctors still seem convinced exercise is a good way to lose weight – unaware of studies showing it can be a morale-sapping waste of time.

One big problem with shedding weight through exercise is that, weight for weight, body fat contains more energy than dynamite. That makes it astonishingly hard to burn off.

Shedding the calories in a blueberry muffin requires a half-hour run on a treadmill – a fact so striking some health campaigners want to see it printed on the packaging.

Exercise can certainly help to burn off fat but the most effective way is to consume fewer calories in the first place, and make sure the ones that are consumed are nutritious rather than junk.

Most alarming of all are the public health messages whose origins are no more credible than a typical Facebook post.

For example, the notion everyone should take 10,000 steps a day comes from nothing more scientific than the brand-name of a pedometer launched in Japan in 1965: Manpo-kei – meaning “Ten thousand steps”.

While it can be a useful fitness target for some, the daunting 10,000 figure has no particular significance.

So if even official advice can’t always be trusted, what can?

Fortunately, the web has resources for bringing ourselves up to speed – if one knows where to look.

Searching with relevant keywords using Google Scholar, the Cochrane Library and PubMed can reveal open-source reviews of the latest findings.

As a rule, research from high-profile institutions published in respected journals is more reliable – especially if the findings are based on large studies.

And then there’s Wikipedia. Once dismissed as the home of conspiracy theorists, pranksters and trolls, it is evolving into a well-referenced entrée to the research literature. The articles on nutrition and fitness are also generally well-balanced, clear and up-to-date.

Anyone concerned about their health should always consult medical professionals. But as with advice on social media, it’s also worth checking their views on nutrition and exercise are backed by the best available evidence. In short, as the motto of Britain’s science academy the Royal Society puts it, “Nullius in verba” – take no one’s word for it.

Robert Matthews is visiting professor of Science at Aston University, Birmingham.