The Paleo diet, endorsed by A-list celebrities including Gwyneth Paltrow, is bad for your heart, a study has found.

People on the Paleo diet were found to have more than twice the amount of a key biomarker linked closely to heart disease.

The biomarker, called trimethylamine-n-oxide (TMAO), is produced in the gut and was raised in Paleo-dieters due to the foods they eat, Australian researchers said.  

The idea of the Paleo diet, also known as the Paleolithic or caveman diet, is to eliminate modern foods and eat what our ancestors would have.

It advocates eating meat, vegetables, nuts and limited fruit, and excluding grains, legumes, dairy, salt, refined sugar and processed oils.  

Although its followers boast of benefits including weight loss, a smaller appetite, and more energy, there has been little research into its effects.

The study at Edith Cowan University, Australia, is the first medical trial into the impact of the Paleo diet on gut bacteria. 

The team compared 44 people on the diet with 47 following a typical diet of an Australian, where the research was carried out.

They measured the amount of trimethylamine-n-oxide (TMAO) in the participants’ blood. 

The compound is made in the gut from foods that are rich in choline, lecithin, and L-carnitine-rich, mainly fish, meat, egg, and dairy. 

High levels have been associated with the hardening of the arteries – major driver in heart disease.

It has also been linked to diabetes and colon cancer, although the exact role of TMAO in these diseases is yet to be confirmed. 

Lead researcher Dr Angela Genoni said: ‘Those who promote the Paleo diet often cite it as beneficial for your gut health.

‘But this research suggests there were adverse differences in those who followed the dietary pattern.’

She said the reason TMAO was so elevated in people on the Paleo diet appeared to be due to the amount of red meat they eat.

However, the lack of whole grain intake is also problematic, according to Dr Genoni, who will presented the findings at the Nutrition Society of Australia conference on Friday.

She said: ‘The Paleo diet excludes all grains and we know whole grains are a fantastic source of resistant starch, and many other fermentable fibres which are vital to the health of your gut microbiome.

‘Because TMAO is produced in the gut, a lack of whole grains might change the populations of bacteria enough to enable higher production of this compound. 

It will be a red flag for fans of the diet, including buyers of Gwyneth Paltrow’s Paleo-inspired book, It’s All Good.

The actress, famous for her interest in health and lifestyle habits, overhauled her diet on the advice of her doctor by cutting out sugar, dairy, wheat, corn, soy, coffee and alcohol after experiencing adrenal stress, anaemia and thyroid problems.   

Celebrities who have reportedly enjoyed a diet rich in meats, fishes and vegetables, and low in wholegrains and legumes, also include Jessica Biel, Megan Fox, Scarlett Johanasson and Jack Osbourne.

Mr Osbourne, who was diagnosed with the autoimmune disease MS in 2012, told ABC News four years ago: ‘Diet is a big thing. I am a firm believer in you are what you eat. 

‘I juice a lot, I try and stick to a Paleo Diet. At its core, I look at MS as inflammation, so I try and eliminate foods that cause inflammation. Dairy, gluten, grains.’ 

And the trainer behind the bodies of Victoria’s Secret models Candice Swanepoel, Irina Shaik and Karlie Kloss, Justin Gelband, swears by it.

However, the diet is not without controversy. In 2014, a report from the British Dietetic Association labelled Paleo a ‘Jurassic fad’.

The statement added: ‘A diet with fewer processed foods, less sugar and salt is actually a good idea, but unless for medical reason, there is absolutely no need to cut any food group out of your diet. 

‘An unbalanced, time consuming, socially isolating diet, which this could easily be, is a sure-fire way to develop nutrient deficiencies, which can compromise health and your relationship with food.’ 

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