Lifestyle

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 gut health kick the kilos obesity science weight loss wellbeing



How to survive a bushfire in your car

IT SOUNDS like a nightmare, but it can happen.

Eight reasons to join the RFS

SPREAD across 93% of Queensland, the Rural Fire Service has about 36,000 volunteers. And you could be one of them.

What if my insurer gives me grief?

CLAIMING your insurance cover after a natural disaster can go one of two ways. It can be a breeze, or like pulling teeth.

Warwick business owners are taking the challenge

No Caption

A couple of Warwick businesses are already right behind the plan.

Sports View with Gerard Walsh

YOU'RE OUT: Australian batsman Glenn Maxwell has been disciplined after comments against a team mate.

Gerard Walsh gives his thoughts on the week in sport.

Rough, tough, in the dirt and off to state

AFL MAD: Skye Elliott is an AFL great, and she hasn't even finished primary school.

Rough, tough, in the dirt and off to state

Local Partners

Businesses challenged to find 100 youth jobs by Christmas

IN THIS, the season of giving, a businessman is challenging business leaders to deliver 100 jobs to unemployed young people for Christmas.


Rose City unites in festive event

Erin and Keely Hilton.

Local performers entertain at Carols in the Park

Safe fun in the water at WIRAC

SWIM STAR: Zac Sorenson having a ball at the GH Foundation Warwick Aquatic Participation Day for adults with a disability.

WIRAC is holding a GH Foundation Aquatic Participation Day today

Creekside Carols are all set to thrill Allora crowd

Chad Wilson, Sarah and Stacey Turner, Greta Barton and Jo Denny at the Allora's Creekside Carols under the Stars   



Photo Deanna Millard / Daily News

ALLORA'S Creekside Carols are on tomorrow night

ABC's Fresh Blood graduates are a Skit Box full of laughs

Sarah Bishop, Greta Lee Jackson and Adele Vuko in a scene from the TV series Wham Bam Thank You Ma'am.

ALL-female comedy trio hitting the mark with new sketch show.

Kim Kardashian West said to be looking for a divorce

Kim Kardashian West is looking to file for divorce from her husband

HBO announces which show will replace Game of Thrones

Diana Rigg, Natalie Dormer, and Hannah Waddingham in a scene from Game of Thrones.

Game of Thrones is definitely not coming back next April

Adele's Carpool Karaoke biggest viral hit on YouTube in 2016

The video has already attracted more than 135 million views

What's on the big screen this week

TJ Miller and Jason Bateman in a scene from the movie Office Christmas Party.

A COMEDY about a rowdy office Christmas party hits cinemas today.

MOVIE REVIEW: Moana is an original adventure in paradise

The character Maui (Dwayne Johnson) in a scene from the movie Moana.

One Boxing Day animated film has a heart as big as the Pacific Ocean

Council opens up on 'secret' private development companies

Ipswich City Council Administration Building, South Street, Ipswich. Photo: Claudia Baxter / The Queensland Times

New website launched by Ipswich City Council

INSIDE STORY: The highlights of your $150 million CBD

GRAND PLAN: The highlights of the Ipswich CBD redevelopment and where they will be located.

Work on city heart's radical transformation to begin next year

VOTE IN OUR POLL: Sand mine opponents face serious dilemma

Public meeting for the proposed sand mine at Maroochydore last week.

Coast MP calls on Minister to stop KRA proposal with stroke of a pen

Developer's grand new multi-million dollar estate

NEW ESTATE: This is the only plan revealed by the property developer's new Billabongs Estate in Agnes Water.

DEVELOPER given the go ahead for a massive estate with 149 homes.

Couple's desperate $550K price drop to sell Gladstone home

Brian Headley and Kirstene Staib are selling their Kin Kora mansion for $750,000.

TELL tale sign of Gladstone's property market.

Ready to SELL your property?

Post Your Ad Here!