Food and Behaviour Research

Donate Log In

Food Affects Behaviour: 20+ Years of FAB Research – What next? - BOOK HERE

Could eating white bread every day ruin your sleep?

Sam Blanchard, Senior Health Reporter for Mailonline


Insomniacs are more likely to have diets abundant in refined carbs which disrupt hormones that control sleep.


'Click-bait' headlines like this one are a Daily Mail speciality - and guaranteed to get more attention than ones worded more soberly, such as this more detailed news article covering the same research:

However, despute the headline suggesting a potential causal effect, this Mail article itself does make clear that this was a purely observational study (involviing over 50,000 post-menopausal women), which means it can't provide any direct evidence of causality.

In fact, the direction of causality could even be the other way around - i.e. sleep problems could lead to more snacking on sugary, refined-carb-rich (i.e. highly-processed) foods.  The article covers this point too, citing a researcher who was not involved in the study.

But it also flags that refined-carb-rich diets were more likely to predict insomnia 3 years later than vice versa, which does rather weaken the 'reverse causality' argument.

So - we can all agree that 'correlation is not causation'. Nonetheless, the basic finding here - that older women whose diets contain more 'refined carbs' have more sleep problems - is consistent with plenty of other evidence that such diets can have numerous other negative effects on health. 

Reducing dietary intake of added sugars and other refined carbohydrates makes sense for many different reasons, as the vast majority of foods that contain these are 'ultra-processed' ones, which:
  • release their energy more quickly, making it more difficult to keep blood sugar levels stable
  • are typically 'energy-dense but nutrient poor' - i.e. they provide calories with few nutrients
  • lack dietary fibre (needed to feed the healthy gut microbes needed for digestive, immune and brain health)
  • are easy to overeat (they usually require little chewing, and often designed to be 'hyper-palatable', or 'more-ish')
  • often contain artificial additives that can negatively affect gut health   
By contrast, diets low in refined carbs, and instead rich in whole, unprocessed foods that provide unrefined carbs - such as whole grains, vegetables and fruits - are associated with better outcomes on amost every measure of physical and mental health.  It would therefore be more surprising if better sleep were not amongst them.

The final quote from one of the researchers is accurate enough, given the careful use of the word 'could':

'The take-home message here is to limit the consumption of highly processed carbohydrates such as added sugars since they could contribute toward or exacerbate insomnia' 

And if headlines like this one might actually encourage more people to do that, it could probably have many other benefits too - including for overburdened health service providers.

For details of the research study, see:

  • A study of women's diets found foods which increase blood sugar hit sleep
  • Those who ate the most refined carbs were 16% more likely to develop insomnia
  • This could be because blood sugar spikes release alertness hormones

Older women who eat a lot of sweets and white bread may be more likely to have insomnia.

A study of food diaries kept by more than 50,000 women in the mid-60s revealed processed grains and sugar are linked to the sleep-stealing condition.

Scientists in New York City suggested eating a lot of sugar could make blood sugar levels vary so much that the body starts to release hormones which keep people awake.

It could also be the case that sleep loss could make people develop cravings and eat more, meaning the effect could run the other way.

But the women in the study were also 16 per cent more likely to develop a new case of insomnia if they ate a lot of the offending foods.

Researchers who tracked the diets of some 50,000 postmenopausal women found those who ate the most foods which raised blood sugar were 11 per cent more likely to say they had insomnia to begin with and 16 per cent more likely to get it within the three year study.

'Our results point to the importance of diet for those who suffer from insomnia,' said lead study author, Dr James Gangwisch, a psychiatrist at Columbia University.

'Avoiding insomnia is therefore another good reason to avoid sweets besides weight control.'

The study did not set out to work out why sweets and refined carbohydrates – which include breads, cakes, pastries and pasta – could impact on someone's sleep.

But Dr Gangwisch said hormonal changes could be to blame.

'When blood sugar is raised quickly, your body reacts by releasing insulin, and the resulting drop in blood sugar can lead to the release of hormones such as adrenaline and cortisol, which can interfere with sleep,' Dr Gangwisch said.

The women in the study had already been through the menopause and had the glycaemic index of their diet measured by the scientists.

This measures the impact food has on someone's blood sugar – foods high in fat or protein have a lower glycaemic index than carbohydrates and sugars, which make blood sugar spike.  

Dr Gangwisch's study found women with the highest dietary glycaemic index scores were 11 per cent more likely to say they had insomnia, compared to women with the lowest.

They were also 16 per cent more likely to develop new insomnia during the three-year follow-up period.

Women whose diet included higher amounts of vegetables, fibre and whole fruit (not juice) were less likely to have insomnia already or to develop it.

Even though whole fruits contain sugar, they also contain fibre that helps minimise spikes in blood sugar, making these foods lower on the glycaemic index.

One researcher not involved with the study, Jose Ordovas from Tufts University in Boston, said the effect could be the other way around.

He suggested women who couldn't sleep may be driven to worse diets – tiredness has in the past been shown to increase junk food intake.  

'Using these findings as the basis for prevention and treatment of insomnia is extremely premature,' Dr Ordovas told Reuters.

Doctors often recommend a low-glycaemic diet to people who need to lower or control their blood sugar.

This includes individuals with diabetes, or who need to lose weight or develop healthier eating habits.

Better sleep could be yet another reason to eat this way, Dr Gangwisch said.

'The take-home message here is to limit the consumption of highly processed carbohydrates such as added sugars since they could contribute toward or exacerbate insomnia,' he added.