Science amiss in the top selling diet books

Along with the new year comes that time when many people are planning lifestyle changes inspired by a trending best-selling diet book.

But are these books really all they are cracked (or is that quacked) up to be? Or does the ideology (far) outweigh the evidence?
 
A 2020 study assessed the claims and author credentials of the top 100 nutritional best-selling books.

The bottomline

Most top sellers contain misinformation and their claims lack scientific basis.

Despite flying off the shelf, they were not an ideal source of sound information. Even when the author has a medical degree or PhD.
 
We should note that most information assessed came from the Google book summary, not the whole book.

Regardless, identifying trustworthy nutrition science is harder than ever before.

Not surprisingly, 80% of books mentioned weight loss or weight management. The median length of a programme was 21 days, with a median weight loss of nearly 7 kg.

If we translate this into an average rate of weight loss, it’s completely unrealistic ­equivalent to nearly 3 kg a week.

Even the rapid weight loss in the Diabetes Remission Clinical Trial (DiRECT) we highlighted in Issue 19 did not come close to this rate.

Using total meal replacements, the DiRECT study aimed to reduce weight by 15 kg over 3 months (just over a one kg a week) – an ambitious, yet more realistic target.

DiRECT also had comprehensive strategies for weight maintenance, a key element missing from many diet books.
 
Nearly one-third of books claimed they could prevent or cure a disease.


The top diseases included diabetes, heart disease, cancer, and dementia. Arthritis, auto-immune diseases, Parkinson’s disease, autism spectrum disorder, and depression also got a look in.
 
Over one in five books also advised how to improve energy levels or lifespan.


The authors provide examples of unsubstantiated claims. We picked out a few gems:
 

• ‘Carbs are destroying your brain’ – Grain Brain
• ‘Skip breakfast, stop counting calories, eat high levels of healthy saturated fat, work out and sleep less, and add smart supplements’– The Bulletproof Diet
• ‘The idea that people simply eat too much is no longer supported by science’– The Adrenal Reset Diet
• ‘Throwing ice cubes in your water to make it more structured’ – Effortless Healing

Given the common themes of weight loss, disease prevention or cure, and lifespan extension we would expect to see some consistent recommendations.

Yet there was little consistency about what components of the diets are beneficial.

For example, many books claim low carb or grain-free is crucial for health, while others support eating grains. Some promote dairy while others completely omit it. There were even inconsistencies on whether low fat or high fat dairy is preferable.
 
So altogether, a complete lack of consensus – unlike evidence-based dietary guidelines where we see consistent messages globally – promoting fruit and vegetables, wholegrain carbohydrates, lean protein sources, and unsaturated fat, while limiting saturated fat and sodium.
 
So, who writes these books?

Over one-third of authors had a medical degree and 6% a PhD. Around half the authors had no degree.

While one-third had been practicing physicians at some stage, other occupations included editors, entrepreneurs, personal trainers, nutritionists, actors, bloggers, reality TV stars, fire fighters, and our personal favourite – a professional pool player.
 
Twenty authors mentioned they had faculty positions, but only 7 of these could be validated. Many had undefined ‘voluntary’ positions. Of concern, one author had 28 of his scientific papers retracted!
 
What’s so troubling about these best-sellers?

Their popularity means they could have a greater influence on public health than peer-reviewed evidence.

Given their evidence-base is sketchy, and there are conflicting claims from book to book, we end up wasting precious time tackling misinformation, exaggeration, and embellishment.

A disturbing element of these books is they tend to prey on people’s insecurities, be it body weight dissatisfaction, lack of energy, or fear of illness.
 
How do you help your clients spot a quack?

We provided some tips in Issue 18 on how to spot misinformation, and have now added to the list:

• If someone sounds off, check them out using resources such as Retraction Watch Database and Quackwatch.

• Catch words such as ‘cure’ or ‘scientific breakthrough’ should set off alarm bells.
• Anyone offering quick or easy weight loss is likely to be a quack.
• Anecdotes ≠ evidence, and so should be treated with caution.
• Anyone selling or promoting supplements make money from their claims, and so should be treated with a healthy dose of scepticism.