The surprise finding, detailed in a paper in Nature journal Nutrition and Diabetes, has prompted University of Melbourne researchers to issue a warning about putting faith in so-called fad diets with little or no scientific evidence.

 Lead author, associate professor Sof Andrikopoulos says this type of diet, exemplified in many forms of the popular Paleo diet, is not recommended–particularly for people who are already overweight and lead sedentary lifestyles.

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He says mass media hype around these diets, particularly driven by celebrity chefs, celebrity weight-loss stories in the tabloid media and reality TV shows, are leading to more people trying fad diets backed by little evidence. In people with pre-diabetes or diabetes, the low-carb, high-fat (LCHF) diet could be particularly risky, he said.

“Low-carbohydrate, high-fat diets are becoming more popular, but there is no scientific evidence that these diets work. In fact, if you put an inactive individual on this type of diet, the chances are that person will gain weight,” said Andrikopoulos, who is a researcher at the University of Melbourne Department of Medicine, based at the Austin Hospital.

“There is a very important public health message here. You need to be very careful with fad diets, always seek professional advice for weight management and aim for diets backed by evidence.” 

Researchers at the University of Melbourne originally sought to test whether high-fat and low-carbohydrate foods would benefit the health of people with pre-diabetes.

They took two groups of overweight mice with pre-diabetes symptoms and put one group on the LCHF diet. The other group ate their normal diet. The mice were switched from a three per cent fat diet to a 60 per cent fat diet. Their carbs were reduced to only 20 per cent. 

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The researchers used mice for the study, because their genetic, biological, and behavioral characteristics closely resemble those of humans. 

After eight weeks, the group on the LCHF gained more weight, their glucose intolerance worsened, and their insulin levels rose. The paleo diet group gained 15 per cent of their body weight. Their fat mass doubled from two percent to almost four percent.

“To put that in perspective, for a 100 kilogram person, that’s the equivalent of 15 kilograms in two months. That’s extreme weight gain,” Andrikopoulos said.

“This level of weight gain will increase blood pressure and increase your risk of anxiety and depression and may cause bone issues and arthritis.

“For someone who is already overweight, this diet would only further increase blood sugar and insulin levels and could actually pre-dispose them to diabetes.

“We are told to eat zero carbs and lots of fat on the Paleo diet. Our model tried to mimic that, but we didn’t see any improvements in weight or symptoms. In fact, they got worse. The bottom line is it’s not good to eat too much fat.”

Prof Andrikopoulos says the Mediterranean diet is the best for people with pre-diabetes or diabetes.

“It’s backed by evidence and is a low-refined sugar diet with healthy oils and fats from fish and extra virgin olive oil, legumes, and protein.”