Updated 29 August 2017

You won't believe what's lurking in your gut

The thousands of microbial species in the human intestine help us digest fibre, make vitamins and help strengthen our immune system.

When we hear the word bacteria we usually think of something negative. There are however many beneficial bacteria, especially in the human intestine.

The bacteria in your gut are strongly linked to your overall health. Anything that causes inflammation or an imbalance in the healthy bacteria in your gut, is bound to make you feel less than good.

But how can we determine the bacteria in our gut? New research has the answer: what you eat, or don't eat, affects the mix of germs in your digestive tract.

The various Lactobacillus bacteria are among the most important ones we need for a healthy gut.

Bacteria strengthen the immune system

Thousands of microbial species thrive in the human intestine, helping people digest fibre and make vitamins and other molecules. They also help strengthen the immune system and protect against potentially harmful bacteria, according to Stanford University School of Medicine researchers.

The rise in farming some 15 000 years ago dramatically changed the human diet, the researchers noted. And in just the last 100 years, people have become increasingly sedentary and less likely to consume fibre-rich whole grains, fruits and vegetables.

Antibiotics, Caesarean sections and other lifestyle changes have also helped shift the composition of microbes in the human gut, the study authors added.

Change of lifestyle over time

To see how "progress" may have affected microbial diversity, the researchers examined seasonal changes in the gut microbes of the Hadza tribe in Tanzania – one of the world's last remaining traditional hunter-gatherer populations.

They rely primarily on meat, berries, baobab (a fruit), tubers and honey. The researchers found their gut bacteria different and more diverse than the gut bacteria of those living in the cities of industrialised countries.

"The 100 to 200 Hadza people sticking to this routine will possibly lose it in a decade or two, maybe sooner. Some are using cell phones now," senior study author Justin Sonnenburg said in a Stanford news release.

"We wanted to take advantage of this rapidly closing window to explore our vanishing microbiota," said Sonnenburg, an associate professor of microbiology and immunology.

Stool samples from the Hadza tribe showed their mix of gut microbes changes with the seasons and their diet.

Loss of diversity

The significant modifications made to the human diet over the past 10 000 years could help explain the loss of diversity in the germs residing in the typical modern digestive tract, the study suggests.

"Surviving hunter-gatherer populations are the closest available proxy to a time machine we in the modern industrialised world can climb into to learn about the ways of our remote human ancestors," Sonnenburg said.

"Our own microbiota can change significantly from day to day, or even within hours, in response to what we've been eating," said Sonnenburg. "Fibre's all that's left at the very end of our digestive tract where these microbes live, so they've evolved to be very good at digesting it. The Hadza people get 100 or more grams of fibre a day in their food, on average. We average 15 grams per day."

The findings were published in the journal Science. 

Food for thought

Some foods can have a negative effect on our gut bacteria and cause indigestion. This includes:

  • Fried or fatty foods like burgers, slap chips, samoosas, koeksisters and doughnuts
  • Dairy products
  • Processed carbohydrates such as pastries and cookies
  • Too many carbohydrates

Image credit: iStock