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Cruciferous vegetables and fermented food could be better than a probiotic, research finds

It’s a market worth $91 billion, but is our love affair with popping a daily probiotic based on bad science? Here’s what the experts say.

Want to improve your immunity, energy or digestion? Modern-day wisdom tells us to pop a probiotic. But is that the best advice? First, a quick science lesson: probiotics are live micro-organisms believed to enhance the gut microbiome and boost health and vitality.

Naturally present in foods such as yoghurt, fermented produce and some cheeses, over the past two decades probiotics have popped up in an array of easy-to-swallow pills, powders and beverages, creating a global market worth $91 billion, and expected to sky-rocket to almost $133 billion by 2027.

Yet rather than fulfilling their health promise, some evidence suggests probiotic supplements don’t help everyone – and, in some cases, can even do more harm than good.

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The cause of consternation? In a recent study from the Stanford School of Medicine, researchers recruited 39 adults with diagnosed metabolic syndrome – a cluster of conditions that can lead to heart disease, diabetes and stroke – and asked them to take a probiotic with strains of bacteria considered beneficial for metabolic and digestive health. The results showed huge variability: some participants had improvements in blood pressure and cholesterol levels, but others, well, got worse.

Even more contentious? Those who did respond well to the probiotics in the study already had an array of friendly bacteria in their microbiome, says Eli Brecher, a registered nutritionist who specialises in gut health. This suggests that probiotics alone won’t transform an unhealthy digestive system.

Indeed, for a healthy gut, popping an acidophilus can be too much of a good thing. “Probiotic supplements aren’t something to take routinely and aren’t necessary for everyone’s microbiomes, which are as unique as our fingerprints,” advises Brecher.

By adding more of a type of bacteria that your gut doesn’t need – however ‘good’ it might be – you risk upsetting your own delicate balance. “Excessive levels of bacteria, whether beneficial or [harmful], can cause problems,” she says.

One common issue? Small-intestinal bacterial overgrowth, which can result in bloating, nausea and abdominal pain. (Um, no thanks.)

What about the main reason probiotics are recommended: as a course correct after a biome-upsetting tangle with antibiotics? There is also contradictory research here. Some studies suggest probiotics could hinder microbiome recovery. Brecher cautions there are even people who shouldn’t take them at all: “They should be avoided entirely by anyone who has a chronically weakened immune system or who has open wounds following major surgery, and anyone with pancreatitis.”

Then, the big question: what’s the actual proof behind the assertion “the more diverse your gut bacteria, the better” within health circles? It might come as a surprise to anyone with scant awareness of nutrition trends, but some experts feel there’s not enough evidence that bacterial diversity boosts immunity or wards off infection. A common example? The fact breastfed newborns are known to have better immunity and fewer infections than formula-fed babies, despite having been shown to have low diversity of bacteria in their guts.

So, what gives? Nicole Dynan is a Sydney-based accredited dietitian who specialises in gut health. She says gut science, and with it our understanding of probiotics, is relatively new.

“Gut science is only 20 years old. In fact, 40 per cent of the bacteria within our gut hasn’t been identified or named yet, so we can’t expect to have all the answers on probiotics. When it comes to the gut, diversity is one thing, but it’s not everything.”

On the plus side, studies have shown probiotic supplements can be helpful for people with conditions such as traveller’s diarrhoea and inflammatory bowel disease. However, there’s no guarantee they’ll make a difference, and evidence shows their benefits are only as a companion to conventional medicine.

The most important thing to know: not all probiotics work the same way. “What we have learnt so far is choosing a strain that is specific to the health condition you are trying to support is key,” says Dynan. “If you have a headache, you want to take a headache pill, not any random drug. Choosing a multi-strain probiotic is just that – you are better off looking for a product that has been tested for the specific benefit you are looking for, otherwise it can be a costly stab in the dark.”

Knowing which one is most suited to your needs may require a consultation with a dietitian or gut specialist, says Brecher. And the brand you pick matters, too. University of New South Wales Associate Professor, Sara Grafenauer, explains not all supplements can survive the acidic conditions in the gut, to reach the bowel in high enough quantities to have any effect. “[This is why] we tend to prefer probiotics in food form, like yoghurt,” she explains. “They provide good nutrition and deliver the probiotic within a food matrix.”

The best foods to boost gut health

According to dietitian Nicole Dynan, while probiotics get a lot of press, prebiotics are the unsung star of the supermarket aisle. So, what are they? “Prebiotics are types of soluble fibre humans can’t digest but that serve as ‘food’ for the beneficial microbes that live in your colon and elsewhere in the body,” she explains. These organisms have been shown to improve calcium absorption, regulate blood sugar and “enhance colonic bacterial fermentation” – science speak for keeping you regular. “These physiological benefits may have positive effects in those with osteoporosis, diabetes and colorectal cancer.” To that end, meet the best gut-friendly foods, designed to support your system, naturally

Kombucha, sauerkraut, kimchi, miso, tempeh 

“Fermented foods such as kimchi and kombucha contain live microbes associated with health benefits,” says Dynan. Just remember, off-the-shelf varieties can be high in salt or sugar, so check the label.


This fermented dairy drink typically contains more probiotic bacteria than yoghurt-based drinks. It’s best consumed on an empty stomach, so that it colonises the gut lining to enhance the absorption of nutrients.

Plain yoghurt 

A dollop of natural or plain Greek yoghurt is a cheap and easy probiotic, says Brecher. Last year, a study of 1000 predominantly female twins showed that plain yoghurt consumption was associated with reduced belly fat.

Asparagus, onions, garlic, leeks, bananas

Good things can come in flavour-some additions to your morning muesli and evening meals – and these foods are all packed with inulin, a fermentable fibre with prebiotic benefits.

Cruciferous vegetables

Simple veggies like broccoli, cauliflower, cabbage, kale and brussels sprouts are all sources of prebiotics, containing compounds including glucosinolates and dietary fibres that can help our gut bacteria flourish.

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