Some people can eat huge amounts of food without putting on a pound, whereas others can’t help piling on weight.

Now scientists may have unlocked a reason why.

Eating junk (ie highly processed food) kills off beneficial stomach bacteria which can protect people against obesity.


The human gut contains around 3,500 different microbial species – there are so many inside us that they weigh three pounds in total

Scientists from King’s College London found that after 10 days of eating McDonald’s, 1,300 of those species had died out.

The finding suggests a reason why some people put on weight, but others don’t – they might be lacking bacteria which defend against obesity.



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A change in gut bacteria could lead to obesity (Picture Rex)

Tim Spector of King’s College London enlisted his student son Tom to eat only McDonald’s hamburgers, chips, chicken nuggets and Coca Cola for a week.

Tom said, ‘Before I started my father’s fast food diet there were about 3,500 bacterial species in my gut, dominated by a type called firmicutes.

‘Once on the diet I rapidly lost 1,300 species and my gut was dominated by a group called bacteriodetes.

‘The implication is that the McDonalds diet killed 1,300 of my gut species.’