News

Fat or thin: How gut bacteria affects our eating

When we can't lose weight, we tend to want to blame something outside our control. Could it be related to the microbiota - the bacteria and other organisms - that colonise your gut?

You are what you eat

Our gut harbours some trillion microorganisms. These are key in harvesting energy from our food, regulating our immune function, and keeping the lining of our gut healthy.

The composition of our gut microbiota is partly determined by our genes but can also be influenced by lifestyle factors such as our diet, alcohol intake and exercise, as well as medications.

What is the human microbiome?

The bacteria in the gut obtain energy for growth when we metabolise nutrients from food. So our diet is a crucial factor in regulating the type of bacteria that colonise our gut.

One key role of the gut microbiota is degrading the carbohydrates we can't digest into short-chain fatty acids. These help regulate our metabolism and are also important for keeping our colon cells healthy.

Changes in our diet can rapidly change the gut microbiota. Generally, a high-fibre diet which is low in saturated fat and sugar is associated with a healthier gut microbiome, characterised by a greater diversity of organisms.

On the other hand, diets high in saturated fat and refined sugars with low fibre content reduce the microbial diversity, which is bad for our health.

Our animal studies have shown that consuming an unhealthy diet for only three days a week has detrimental effects on the gut microbiota, even when a healthy diet is eaten for the other four days.

This may be because the gut microbiota are under selective pressure to manipulate the hosts' eating behaviour to increase their own fitness. This may lead to cravings, akin to your system being "hijacked" by your microbiota.

Can gut microbiota changes lead to obesity?

Bacteria in humans fall into two major classifications: bacteroidetes and firmicutes. Obesity is associated with a reduction in the ratio of bacteroidetes to firmicutes but weight loss can reverse this shift.

Many studies have found that the gut of an obese person is more likely to contain bacteria that inflame the gastrointestinal tract and damage its lining. This allows the bacteria in the gut to escape.

We still don't know definitively if changes in the gut microbiota from an unhealthy diet can contribute to obesity.

Most evidence supporting this hypothesis comes from animal studies; for instance, the transfer of faecal material from an obese human can lead to weight gain in a recipient mouse.

One possibility is that the obese microbiota may be more efficient in harvesting energy, in part, by influencing the host to eat foods which favour its growth. This could ultimately contribute to weight gain.

Gut changes after weight-loss surgery

Bariatric surgeries such as gastric bypass, are one of the most effective treatments for obesity because they reduce the size of the stomach.

This limits how much food can be eaten and has also been shown to promote the release of hormones which make us feel full.

But other factors may be involved. Intriguingly, some patients report a shift in food preference away from energy-dense foods after surgery. This may contribute to the success of the procedure.

Gastric bypass-induced weight loss has also been associated with increased diversity of the gut microbiota. But how much this contributes to the success of the procedure remains to be determined.

One possibility is that the changes in food preferences reported in bariatric patients may relate to changes in the composition of their gut microbiota.

How gut microbiota affect our behaviour?

Apart from regulating gut health, there is compelling experimental evidence that gut microbiota play a role in regulating mood.

Several studies have shown that depression is associated with changes in the gut microbiome of humans.

Depressed patients showed changes in their abundance of firmicutes, actinobacteria and bacteroidetes.

When these patients' gut microbiota was transferred to mice, the mice showed more depressive behaviour than mice that received biota from healthy people.

More work still needs to be done as it is unclear whether this may indicate a causal relationship, or be related to other factors associated with depressive disorders such as a poor diet, changed sleep patterns and drug treatment.

Emerging evidence suggests that gut microbiota can influence other behaviours through the "microbiota-gut-brain axis".

Put simply, the gut and the brain communicate in part via the microbiota, which links the emotional and cognitive centres of the brain with our intestinal functions.

Recent work from our lab showed that rats consuming diets high in saturated fat or sugar, for just two weeks, had impaired spatial memory.

These rats consumed the same amount of energy as the control rats (those on a regular diet) and were also a similar body weight.

We found that the memory deficits were associated with changes in the gut microbiota composition and genes related to inflammation in the hippocampus, which is a key brain region for memory and learning.

Similar memory deficits have also been reported when healthy mice were transplanted with microbiota from overweight mice who had been fed a high-fat diet.

Together, studies such as these suggest the gut microbiota could play a causal role in regulating behaviour. This may, in part, be due to the different microbiota profiles influencing the production of key transmitters such as serotonin.

What can you do now?

Further research is needed into the relationship between poor diet, the gut microbiota and behavioural changes. In the long term, such knowledge may be harnessed to develop targeted therapeutic interventions to replace relevant microbiota diminished by an unhealthy lifestyle.

Meanwhile, the good news is that the gut microbiota can change relatively quickly and we have the capacity to promote the growth of beneficial bacteria which may ultimately improve a range of health outcomes. Eating a healthy diet of unprocessed foods, including adequate fibre, avoiding excess alcohol and getting enough exercise are key.

Margaret Morris
Professor of Pharmacology, Head of Pharmacology, UNSW Australia

Jessica Beilharz
PhD candidate, UNSW Australia

This article first appeared at The Conversation. It is part of a series which you can check out here.

Topics:  bacteria general-seniors-news health kick the kilos obesity science weight loss wellbeing



Sea level rise is a myth: reader

Rising sea level prediction for Coffs Harbour.

What's got the Coffs Coast talking?

Sand man takes to the high seas

SAND ARTIST: John Thiering recently performed on a cruise.

Sand artist seizes opportunity to perform on cruise ship.

A hundred years of selfless service

The Pacific City Lions Club are just one of the local Lion's clubs that will be serving up food for the big day.

Lions Clubs get ready to celebrate 100th birthday.

Local Partners

Cheaper building fees are here to stay

COFFS Harbour City councillors voted to waiver developer contributions and make building secondary dwellings cheaper.


What to expect at Birds of Tokyo's Ipswich gig

The band will perform at the Racehorse Hotel on Friday.

BAND member Glen Sarangapany talks music, pub grub and doing shoeys

Petula Clark delighted to sing live for Australian fans

STILL TOURING: English singer Petula Clark is coming to Queensland.

English star Petula Clark still puts on a great show, even at 84.

Do you really know your road rules?

Cars travel around the roundabout at Villiers and Fitzroy Street. Photo Adam Hourigan / The Daily Examiner

List of the top 10 most misunderstood road rules in NSW.

Sam Armytage and Tom Cruise? Saaaaay what?

SAMANTHA Armytage has hit back at rumours she’s dating Tom Cruise, following reports the pair had hit it off during an interview on Sunrise.

Musical tribute to flood volunteers released

Songwriter honours flood volunteers who helped their neighbours.

Lismore songwriter Simon Thomas was moved by strangers' kindness

Karl Stefanovic's rant about Schapelle Corby 'a bit rich'

Karl Stefanovic is sick of hearing about Schapelle Corby.

Maybe he just wanted to make himself the story.

Could Schapelle be heading for Gladstone?

Australian Schapelle Corby is escorted by Bali Police at the parole office in Denpasar, Bali, Indonesia, 27 May 2017.

Schapelle's mother teases her free daughter could be Gladstone bound

Six things you never knew about Men in Black

Mushu the pug

It's been 20 years since Men in Black first hit cinemas

10 strange stories behind famous sex scenes

Khaleesi and Khal Drogo in a steamy moment.

Every set has their own way of filming sex scenes

HBO spills new details on Game of Thrones’ final season

Game of Thrones’ eighth and final season will only have six episodes.

New details about what to expect from the eighth, final instalment.

This is real estate's billion-dollar man

Bob Wolff at AREC with John McGrath of McGrath Real Estate.

They don’t call him the “Billion dollar man” for nothing

Man's amazing comeback from monster crisis

Pat O'Driscoll agents Penny Keating and Doug Webber sold 56 Agnes St, The Range at auction over the weekend.

NOT long ago, he sold his possessions to pay staff. Now he's back.

Jetty views don't come any better than this

Property Camperdown St

The Real Estate Property Guide is online now

Kids will love living in this new Coffs Harbour estate

FAMILY FRIENDLY: This children's playground is the latest family-friendly feature of the Elements@Coffs estate.

Local land estate unveils newest family friendly feature

How Toowoomba house prices compare in Australia

For sale sign in front of home.

Here's what $700,000 will buy you in Toowoomba, Brisbane and Sydney

Ready to SELL your property?

Post Your Ad Here!