According to a study published in the European Journal of Nutrition by researchers at Australia's Edith Cowan University, Paleo adherents may have twice the amount of a blood biomarker strongly linked with heart disease, trimethylamine-n-oxide (TMAO), in their bodies. This is likely the first major study to test the effects of the Paleo diet on the human gut microbiome.

"Many Paleo diet proponents claim the diet is beneficial to gut health, but this research suggests that when it comes to the production of TMAO in the gut, the Paleo diet could be having an adverse impact in terms of heart health," lead researcher and Edith Cowan University lecturer Dr. Angela Genoni said in a press release.

"We also found that populations of beneficial bacterial species were lower in the Paleolithic groups, associated with the reduced carbohydrate intake, which may have consequences for other chronic diseases over the long term."

TMAO is produced by gut bacteria called Hungatella during metabolism of certain foods such as meats and eggs, and has been shown to impact metabolism of cholesterol, including cholesterol deposition and removal from artery wall cells. LDL Cholesterol build-up can clog or harden arteries, leading to heart disease and heart attacks. Newsweek cited previous studies which have shown that higher TMAO levels are associated with a significantly increased risk of suffering a major cardiovascular event.

The study included 44 people who follow the Paleo diet and 47 people who followed a standard diet based on national health guidelines. According to the Mayo Clinic, the typical Paleo diet avoids carbs, legumes, dairy and processed foods in favor of protein-dense foods such as lean red and white meat, fish, vegetables and certain fruits.

Of the Paleo diet followers, 22 were further categorized as "strict" followers who ate less than one serving each day of grains and dairy. The rest were deemed "Pseudo-Paleo" dieters, who followed the diet more loosely. Over the course of a year, the researchers analyzed biological data, samples and the diets of both groups.

The researchers found that the Paleo diet followers had a higher count of TMAO-producing Hungatella bacteria. The "strict" Paleo followers had the highest levels of blood TMAO levels, while those who loosely followed the diet but ate more grains and dairy had lower levels of TMAO in their blood comparable to those following the standard diet.

While noting the need for further research, the authors wrote that the results support keeping gut-regulating, heart-healthy grains in your diet and reconsidering the amount of meat recommended by the Paleo diet.

"Because [trimethylamine N-oxide] is produced in the gut, a lack of whole grains might change the populations of bacteria enough to enable higher production of this compound," Genoni said. "Additionally, the Paleo diet includes greater servings per day of red meat, which provides the precursor compounds to produce [trimethylamine N-oxide] and Paleo followers consumed twice the recommended level of saturated fats, which is cause for concern."

Cardiovascular disease is the top cause of death globally, according to the World Health Organization.

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