White bread does not cause weight gain as previously suggested. Picture: Supplied

White bread has always been deemed unhealthy. 

But there's probably no need to give it up and turn to handmade sourdoughs from fancy bakeries, new research suggests. Eating the mass-produced white loaves won't necessarily make you fat - contrary to popular belief, scientists claim.

Instead, it completely depends on how your body, specifically stomach bacteria, reacts to it.

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Israeli researchers gave 40 participants either handmade sourdough or white bread, The Independent reports.

Blood sugar levels spiked in both groups, a known risk factor of obesity in people eating high glycemic index foods.

But neither were found to put on more weight than another, according to the researchers.

This provided the biggest indicator that the gut microbiome is responsible for weight gain, they said.

They managed to revert blood sugar levels back to normal by tailoring diets for each participant based on their stomach bacteria.  

Dr Evan Elinav, of the Weizmann Institute of Science in Israel, said: 'There is this notion that some bread is better than others. Industrial bread is seen as bad and home-made sourdough is seen as good.

We found that just like any other food, our responses to bread are completely personal.

'This personalised effect is there for every single food. There is not one single good or bad or super food.'

Sales of white bread less filling and lower in fibre than wholewheat have slumped by 75 per cent in the past four decades, data has showed.

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While retailers are reporting an increased demand for artisan loaves, such as sourdough bread.

Previous research has found that those who eat three slices of white bread a day are more likely to be obese.

Spanish scientists discovered they were 40 per cent more likely to be overweight than those who ate it once a week.   

The new findings were presented at the American Association for the Advancement of Science meeting in Boston