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


Stay Connected

Update your news preferences and get the latest news delivered to your inbox.

This is why we will keep writing shark stories

ONCE BITTEN: Evans Head resident Craig Ison with the board he was riding when he was attacked by a great white shark at Main Beach.

The media is constantly accused of sensationalising the shark issue

Guard 'heard screaming', saw Byron woman next to dead cop

epa05516083 Australian national Sara Connor (C) participates in the reconstruction of the death of a police officer at Kuta beach in Bali, Indonesia, 31 August 2016. Australian Sara Connor and British national David Taylor, were arrested by Bali police, and are accused of murdering a local policeman on Kuta Beach. The body of police officer Wayan Sudarsa was found with deep wounds to his head and neck on Kuta beach on 17 August 2016.  EPA/MADE NAGI

Security guard 'heard screaming', saw Byron woman next to dead cop

251 Lismore Go Fund Me campaigns raise $333,500

Lennox Head mum Sarah Rosborg's dream of building a safe house for young victims of sex abuse in Kenya has become a reality. In the end, $200,000 was raised in less than one month and Rafiki Mwema was able to build the 'Queen's Castle'.

Crowdfunding magic room for guests, death, sick kids, pets

Local Partners

An emotional Mike Baird: 'There was great personal cost'

Mr Baird said there would be a Liberal party-room meeting and a spill of leadership positions next week.

Mr Love brings music and spirituality to the Bay

TOURING: Hawaiian musician Mike Love will perform in Mullumbimby this weekend.

Mike Love returns with his The Beginning Of Days 2017 Tour

Puppetry of the Penis secrets revealed ahead of show

The famed Puppetry of the Penis is coming to the Sunshine Coast for shows in Noosa and Caloundra.

WARNING: This interview contains adult themes and traces of nuts

Northern Rivers murder mystery takes out award at Flickerfest

MURDER MYSTERY: Northern Rivers young actress Yasmin Honeychurch in a still from the award-wiining film In a Canefield by Emily Avila and Coralie Tapper.

Finding'little star' brought film shoot to the region.

No Plan, Bowie's final music EP, released

NEW: Artwork for David Bowie's posthumous 2016 EP, No Plan.

David Bowie's 28th and final album

Mr Love brings music and spirituality to the Bay

TOURING: Hawaiian musician Mike Love will perform in Mullumbimby this weekend.

Mike Love returns with his The Beginning Of Days 2017 Tour

Married At First Sight: Ipswich bachelor seeks love

READY FOR IT: Ipswich man Simon McQuillan will appear on the upcoming new season of Married At First Sight.

Romance would top off recovery for Booval man

Dinky-di Denyer: Family Feud favourite hosts Oz Day party

Grant Denyer will host Channel 10's Australia Day concert from the Sydney Opera House.

GRANT Denyer shares his Australia Day traditions ahead of concert.

Chelsea Handler blames the Kardashians for Donald Trump win

Chelsea Handler pictured in a scene from her talk show in Los Angeles.

TALK show host blames rise of reality TV family for election result.

Law & Order’s Trump inspired episode is still in limbo

The cast of Law & Order: SVU season 18, from left, Kelli Giddish, Raul Esparza, Mariska Hargitay, Ice-T and Peter Scanavino. Supplied by Channel 10.

SHOW'S mastermind unsure if or when twice-delayed episode will air.

Thousands of jobs part of $1b retirement village project

THIS YEAR: An artist impression of the new Aveo retirement village in Springfield.

Aveo Springfield unveiled this month, homes ready by July

KNIFE-EDGE: The housing tightrope we now face

Even the smallest interest rate rise will be hard for some to handle.

One if five home owners at risk, according to new analysis

Historical home leaves family's hands after 75 years

SALE CONFIRMED: The Gympie Regional   Realty team which sold the Ramsey property are (back) Mel Gastigar, Dorothy Palmer and Margaret Cochrane, with (front) home seller Terri-Jayne Ramsey.

Ramsey family played a huge role in Gympie's growth.

Pat Rafter's $18m Coast home proves hot property

PAT'S PAD: The Sunshine Beach home of tennis ace Pat rafter is on the market for a record price.

"It's a record for our company and for the Sunshine Coast.''

INTERACTIVE MAP: Which Northern Rivers towns boomed in 2016?

BOOM TOWNS: While Ballina properties continued to attract top dollar in 2016, it was areas to the south that experienced price hikes, including Wardell, Evans Head and Woodburn.

Click on our map to find the median sale price in your town

Ready to SELL your property?

Post Your Ad Here!