Eating junk food kills stomach bacteria which protect against obesity, diabetes, cancer, heart disease, inflammatory bowel conditions and autism, fresh studies have found.
The human gut contains around 3,500 difference microbial species, which together make up some three pounds in weight.
Scientists now believe a diet based on a limited range of highly processed foods, rather than those found in a balanced, healthy diet, can wipe out the number of stomach flora by more than a third.
The discovery could explain why some people put on weight while others don’t, despite eating roughly similar amounts of fat, sugar, protein and carbohydrates.
The finding emerged from studies conducted by Tim Spector, professor of genetic epidemiology at King’s College London.
He enlisted the help of his 23-year genetics student son Tom, who agreed to spend 10 days on a fast-food-only diet of McDonald’s hamburgers, chips, chicken nuggets and Coca Cola.
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”.
Almost two thirds of adult Britons are overweight.