• Dr Zoe Williams and tests the effects of a high fat diet on the body. (BBC Worldwide)Source: BBC Worldwide
The dieting world keeps fluctuating between its lead villains. Now that we officially hate sugar, can every meal be loaded with butter, bacon and avocado instead?
Signe Dean

10 Mar 2017 - 2:35 PM  UPDATED 8 Jan 2018 - 12:37 PM

When the low-fat-everything craze peaked in the late '90s, Australians did not magically become leaner and healthier. Instead, twenty years on, we have an unprecedented level of obesity on our hands.

By now we have figured out that the other side of a ‘low fat’ food label should say ‘probably high sugar, will make you fat anyway’. As the case against sugar is mounting, that leaves dietary fats in an interesting situation. No longer the enemy, fatty foods are enjoying a comeback of sorts.

The trend is especially prominent within circles adopting the #keto lifestyle. On social media it stands for a parade of athletic bodies, hard-boiled eggs, odd-looking smoothies and a truckload of avocados served in every way imaginable. Keto is short for ‘ketogenic diet’, a scientific approach to going (very) low carb.

“The idea of a ketogenic diet is that you restrict carbohydrates to such a low level that your body is mostly using its fat, or the fat that you eat, as its energy store,” explains research scientist and nutrition expert Dr Tim Crowe. This process is called ketosis.

“When it's doing that, it produces these things called ketones in your bloodstream. Everybody has ketones in their blood, but on a ketogenic diet the levels are much higher.”

The ketogenic diet is actually a medical treatment for children with hard-to-treat epilepsy; when the brain starts using ketones instead of glucose as an energy source, this can also reduce the frequency of epileptic seizures. But lately ketosis is starting to become popular outside its narrow medical application.

“Over the last five or ten years there's been a lot of research done on that, that there is a potential place for [a low carb diet] in managing type 2 diabetes and, for some people, for weight loss,” explains Crowe.

For your body to enter ketosis, the carb intake has to be shockingly low, making it an extremely restrictive diet. A typical recommendation is to stick to 20-50 grams of daily carbs; two or three pieces of fruit or a single cup of rice could blow your entire carbohydrate budget for the day. Going into ketosis can also produce temporary symptoms such as brain fog, weakness and tiredness, which dieters sometimes call the “keto flu”. According to Crowe, all this makes it hard for people to stick to keto in the long term.

As a medical treatment, a ketogenic diet is used under strict medical supervision. If you’re doing it on your own, it can be difficult to make sure you’re balancing your micronutrients correctly, since foods high in protein and fat can easily have too much sodium, or not enough vitamins.

Furthermore, all fats are not made equal. Nutritionists advise that a healthy diet should include monounsaturated and polyunsaturated fats that largely come from things like olive oil, nuts, seeds, avocado and oily fish.

“These shouldn’t displace other healthy foods like vegetables, fruits, and wholegrain foods,” says dietitian Kacie Dickinson from Flinders University. But if you’re going #keto, it can’t all be butter and bacon like the Atkins diet of yore.

“Where there's a problem is if you eat a high-fat diet that's full of highly processed food as well,” says Crowe.

To see what happens to the body when you stuff it full of bad fats, researcher Matt Cocks from Liverpool John Moores University conducted a trial with 10 men and 10 women, putting them on a high-fat diet for seven days. The participants’ calorie intake was composed of 60 per cent fat – they gorged on things like sausages, bacon, cheese and hash browns.

Cock’s research features in the latest series of Dr Michael Mosley’s Trust Me I’m A Doctor (Mondays 8.30pm on SBS, then on SBS On Demand).

“From time to time, most of us will eat far more than we should in the way of fatty and sugary foods. New research, however, suggests that overindulgence affects men and women differently,” Mosley explains. Mosley’s colleague on the show, Dr Zoe Williams, finds out more. “We all know that too much fat can cause issues with our weight and our heart health, but a new problem that’s only just coming  to light is that eating a lot of fat can also affect how our bodies process other foods, in particular carbohydrates,” she says.

The goal of Cock’s study was to see whether such a diet affects the ability to deal with blood sugar changes – if your body can’t deal with glucose spikes that becomes a risk for type 2 diabetes. Unsurprisingly, the unhealthy fats did contribute to the problem, especially for male participants. However, the trial was very small, so experts say it is hard to draw sound conclusions from it.

“It's an interesting study to look at mechanisms, but they also ate 50 per cent more calories,” Crowe emphasises. “Anybody eating that amount of extra energy, even if it was coming from healthy fats, would start gaining weight.”

“Fat may have a role in suppressing appetite and energy intake through its effects on our digestive system,” adds Dickinson. “We need to understand this better because eating lots of fat in the diet can still lead to eating too many calories and eventually contribute to gaining extra weight.”

Ultimately, a high-fat, low-carb diet that puts your body in ketosis may work for weight loss in some people, but despite a few evangelical proponents it’s neither a magic bullet nor is it widely recommended, explains Crowe.

“It's not miles in front of other approaches somebody could choose.”


Any dietary information in this article does not constitute medical advice and readers should consult their healthcare providers before attempting any extreme lifestyle changes.

Love the story? Follow the author here: Twitter @nevertoocurious.

Watch Trust Me I'm A Doctor Mondays 8.30pm on SBS, then watch it on SBS On Demand

Bacon image by cookbookman17 via Flickr. 

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