McDonald's and the Microbiome: What Effect Does Junk Food Have on Gut Bacteria?
When Morgan Spurlock famously spent a month eating large portions of McDonalds for the purposes of his documentary Supersize Me, he gained weight, damaged his liver and claimed to have suffered addictive withdrawal symptoms. This was popularly attributed to the toxic mix of carbs and fat plus the added chemicals and preservatives in junk foods. But could there be another explanation?
We may have forgotten others who really don't enjoy fast food. These are the poor creatures that live in the dark in our guts. These are the hundred trillion microbes that outnumber our total human cells ten to one and digest our food, provide many vitamins and nutrients and keep us healthy. Until recently we have viewed them as harmful – but those (like salmonella) are a tiny minority and most are essential for us.
Studies in lab mice have shown that when fed an intensive high fat diet their microbes change dramatically and for the worse. This can be partly prevented by using probiotics; but there are obvious differences between us and lab mice, as well as our natural microbes.
A recent study took a group of Africans who ate a traditional local diet high in beans and vegetables and swapped their diet with a group of African Americans who ate a diet high in fat and animal proteins and low dietary fibre. The Africans fared worse on American-style food: their metabolism changed to a diabetic and unhealthy profile within just two weeks. The African Americans instead had lower markers for colon cancer risk. Tests of both groups showed very different microbiomes, the populations of microbes in their guts.