Why does the intermittent fasting and the keto diet give you bad breath? We investigate.

Those dedicated to the cult of intermittent fasting or the ketogenic diet will be familiar with one of its unspoken side effects, which has nothing to do with increased muscle definition or your waistline.

Yep… we’re talking about bad breath and it’s even got its own Instagram hashtag.

While the regime is famed for its ability to give the dieter unbounded energy, laser sharp mental focus and unparalleled fat-burning capabilities, it’s time we talk about your body’s other awkward (and breathier) response.

To get down to it, we racked the brains of dentist and bad breath specialist, Dr Geoffrey Speiser of the Australian Breath Clinic, and fear not because non-judgemental advice is coming your way.


How does #ketobreath differ to normal bad breath?

So how do you know if your case of whiffy breath is because your diet is paying off, or is a sign that you need to revise your dental hygiene ASAP?

According to Dr Speiser there’s a definite way to tell.

He describes ketone-infused breath as having a “fruity alcohol type of smell”, versus the pungent notes of say ‘rotten egg-esque’ dragon’s breath.

Members from fitness forum also describe the scent as “metallic” or even more delightfully so, as a kind of ” hamburger-meat” aroma.



Why does intermittent fasting and the ketogenic diet cause bad breath?

As Dr Speiser explains, releasing ketones – a gaseous bodily compound – is a normal side effect of dieting and the breakdown of body fat.

“This would lead to ketosis,” he says. “Ketosis releases ketones which are a volatile odorous compound.”

Dr Speiser also says diets high in protein, such as the ketogenic or paleo can also lead to an increased chance of bad breath, but this smell differs from ‘ketone-infused’ breath.

“Bad breath comes from the breakdown of proteins into amino acids and waste products called volatile sulphur compounds (VLC). These VLC are the bad breath smells,” he says.

“Ninety per cent of protein breakdown is the white coating on the tongue surface, while 10 per cent is from dairy products such as cheese and milk.”


Need some help cutting sugar from your diet? Sarah Wilson has three tried and true tips that will help:

Video by MMC



How do you treat #ketobreath?

Although this is a natural process of your metabolic system doing its job, Dr Speiser notes it’s a lot more common in people who don’t have a proper dental hygiene routine.

While Dr Speiser has developed a special machine which can read the gases in your mouth to pinpoint its pongy origins – should you find yourself on the receiving end of an awkward chat from a family member, friend, or even worse, a date – he says staying hydrated, using mints, and upping your dental hygiene will help too.

For a thorough clean, he also recommends tongue cleaning – something beauty guru Zoe Foster Blake swears by, too.

Writing for Mamamia in 2012, Zoe said this of the life-changing technique:

“I use a tongue brush [like this one here] and tongue gel every morning and night. And while my dear fiancé was far too elegant to ever say I had unsavoury breath, he made a point of telling me it was truly a minty-fresh dream since bringing in the tongue brush.

“It’s part of my routine now, takes 30 seconds, and according to the woman, is more important than teeth brushing for breath.”


Now rejoice, because you can have your high-protein chicken and avocado salad and eat it too… just don’t forget to stay hydrated and invest in a tongue-cleansing device.

You’re welcome.

Have you struggled with bad breath while on a ketogenic or diet involving intermittent fasting? Tell us about your experiences below! Group therapy is open in the comments.

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