Lab Notes: Is fast food making children stupid? Don't swallow the stories


Junk food rots your brain, scientists say. Well, actually, I just made that up. What scientists have really shown is that feeding junk food to young children from the age of three "may be associated" with a slightly lower IQ score at the age of eight.

Words are as important in science as in a court of law. As any good epidemiologist will point out, given 0.5 the chance, association does not automatically mean causation. Because one event (junk food in early life) can be tied statistically to another (slightly lower IQ five years later), it doesn't necessarily follow that one causes the other.

The study in question, published last week in the Journal of Epidemiology and Community Health, was carried out as part of the Avon Longitudinal Study of Parents and Children (Alspac), which is tracking the long-term health and well-being of some 14,000 children born in 1991 and 1992.

Scientists at the University of Bristol wanted to test the hypothesis that a more "healthy" diet in childhood would be associated with an increase in intelligence. They wanted to see whether there was a difference in IQ scores between children fed on a diet rich in salads, pasta, rice, fish and fruit, and children given processed food with high fat and sugar content, such as crisps, fizzy drinks, chips and burgers.

The trouble with such studies is the influence of confounding factors. A mother (and it is usually the mother) who feeds her children a health-conscious diet may also be more likely to be a woman who reads to her kids at bedtime. So is it the diet, or the reading at bedtime that makes those children bright in later childhood? Or is it neither?

The scientists behind the study obviously tried to take such confounding factors into account by "controlling" for social class, maternal age at birth, type of housing, and maternal education. But even so, there is always the nagging possibility that a bad diet is just a marker for something else that really is affecting a child's intellectual development.

It may be, for instance, that a mother's intelligence, which has a heritable component, is linked with the likely diet of her children. Interestingly, this study did not control for maternal intelligence, though the authors of the study believe that controlling for maternal education should have eliminated this as a confounding factor.

Another potential source of error is the nature of the questionnaires used to assess the diet of the children. The mothers were asked to complete "food frequency" forms at the age of three, four, seven and eight-and-a-half years.

An intelligent mother may have filled in the form in a less-than-honest way, perhaps reflecting her health-conscious intentions rather than the actual reality – processed foods may be more convenient for a busy mum who is aware that it may not look too good if she is seen to be relying on them too much.

So it is perhaps easy to see why the scientists used carefully phrased words to conclude their scientific paper: "In this population of contemporary British children, a poor diet, associated with increased intake of processed foods, fat and sugar, in early childhood may be associated with lower IQ at the age of 8.5 years."

Interestingly, the title of the paper is even more circumspect: "Are dietary patterns of childhood associated with IQ at 8 years of age?"

This headline went through an intriguing evolution in the course of its development from press release ("Processed-food diet in early childhood may lower subsequent IQ") to splash headline in the Daily Mail: "Junk food diet hits a child's IQ"). But the one thing that this study has not yet shown is that junk food lowers a child's IQ.

Start your day with The Independent, sign up for daily news emails
ebooksAn introduction to the ground rules of British democracy
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Massage Therapist / Sports Therapist / Physio / Osteopath

£12000 - £24000 per annum: Recruitment Genius: An opportunity has arisen for o...

Recruitment Genius: Account Manager / Sales Executive - Contract Hire

£35000 - £60000 per annum: Recruitment Genius: This industry leader provides c...

Recruitment Genius: Project Coordinator

£28000 - £30000 per annum: Recruitment Genius: A Project Coordinator is requir...

Recruitment Genius: Area Sales Manager - Midlands

£20000 - £25000 per annum: Recruitment Genius: This is an exciting opportunity...

Day In a Page

John Palmer: 'Goldfinger' of British crime was murdered, say police

Murder of the Brink’s-MAT mastermind

'Goldfinger' of British crime's life ended in a blaze of bullets, say police
Forget little green men - aliens will look like humans, says Cambridge University evolution expert

Forget little green men

Leading evolutionary biologist says aliens will look like humans
The Real Stories of Migrant Britain: An Algerian scientist adjusts to life working in a kebab shop

The Real Stories of Migrant Britain

An Algerian scientist struggles to adjust to her new life working in a Scottish kebab shop
Bodyworlds museum: Dr Gunther von Hagens has battled legal threats, Parkinson's disease, and the threat of bankruptcy

Dying dream of Doctor Death

Dr Gunther von Hagens has battled legal threats, Parkinson's disease, and the threat of bankruptcy
UK heatwave: Temperature reaches 39.8 degrees on Central Line - the sweatiest place in London

39.8 degrees recorded on Tube

There's hot (London) and too damn hot (the Underground). Simon Usborne braved the Central line to discover what its passengers suffer
Kitchens go hi-tech: From robot chefs to recipe-shopping apps, computerised cooking is coming

Computerised cooking is coming

From apps that automatically make shopping lists from your recipe books to smart ovens and robot chefs, Kevin Maney rounds up innovations to make your mouth water
Jessie Cave interview: The Harry Potter star has published a feminist collection of cartoons

Jessie Cave's feminist cartoons

The Harry Potter star tells Alice Jones how a one-night stand changed her life
Football Beyond Borders: Even the most distruptive pupils score at homework club

Education: Football Beyond Borders

Add football to an after-school homework club, and even the naughtiest boys can score
10 best barbecue books

Fire up the barbie: 10 best barbecue books

We've got Bibles to get you grilling and smoking like a true south American pro
Wimbledon 2015: Nick Bollettieri - Junk balls and chop and slice are only way 5ft 1in Kurumi Nara can live with Petra Kvitova’s power

Nick Bollettieri's Wimbledon Files

Junk balls and chop and slice are only way 5ft 1in Kurumi Nara can live with Petra Kvitova’s power
Ron Dennis exclusive: ‘This is one of the best McLaren teams ever – we are going to do it’

‘This is one of the best McLaren teams ever – we are going to do it’

Ron Dennis shrugs off a poor start to the season in an exclusive interview, and says the glory days will come back
Seifeddine Rezgui: What motivated a shy student to kill 38 holidaymakers in Tunisia?

Making of a killer

What motivated a shy student to kill 38 holidaymakers in Tunisia?
UK Heatwave: Temperatures on the tube are going to exceed the legal limit for transporting cattle

Just when you thought your commute couldn't get any worse...

Heatwave will see temperatures on the Tube exceed legal limit for transporting cattle
Exclusive - The Real Stories of Migrant Britain: Swapping Bucharest for London

The Real Stories of Migrant Britain

Meet the man who swapped Romania for the UK in a bid to provide for his family, only to discover that the home he left behind wasn't quite what it seemed
Cheaper energy on the way, but it's not all sunshine and rainbows

Cheaper energy on the way, but it's not all sunshine and rainbows

Solar power will help bring down electricity prices over the next five years, according to a new report. But it’s cheap imports of ‘dirty power’ that will lower them the most