Health Risks Associated with the Paleo Diet

Health Risks Associated with the Paleo Diet

By By Tracey Walton wlr team

Low carb high fat (LCHF) diets such as the Paleo, or Caveman, diet have been fashionable in recent years. But emerging research shows there's cause for concern about long term health implications. We report on two recent studies.

Cardiovascular: Heart Health

Study from Edith Cowan University Australia, published in the European Journal of Nutrition July 2019

Key Takeaways

  • People following a Paleo Diet have twice the amount of a blood marker closely linked to heart disease
  • Beneficial gut bacteria are lowered in those adhering to Paleo type diets
  • Lack of whole grains and starchy carbs probably major cause

The controversial Paleo (or 'caveman') diet advocates eating meat, vegetables, nuts and limited fruit, and excludes grains, legumes, dairy, salt, refined sugar and processed oils.

In this research, people who followed the Paleo diet had twice the amount of a key blood biomarker linked closely to heart disease.

The research from Edith Cowan University Australia, published in the European Journal of Nutrition, measured the amount of trimethylamine-n-oxide (TMAO) in participants' blood.

High levels of TMAO, an organic compound produced in the gut, are associated with an increased risk of heart disease, which kills 460 people every day in the UK according to the British Heart Foundation.

The Study

Researchers compared 44 people on the Paleo diet with 47 following a normal diet.

The Paleo diet group were people who had adhered to the diet for at least 1 year and consumed no more than 1 serving a day of grains and dairy products.

The control group had made no changes to their diet in the previous year, and followed a relatively healthy diet which included grains, legumes and dairy or alternatives.

Researchers ran a range of tests on the two groups including blood chemistry and microbiota analysis.

The Results

The Paleo diet group had twice the amount of (TMAO) a blood biomarker closely linked to heart disease.

Lead researcher Dr Angela Genoni said:

"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."

The research also found that populations of beneficial bacterial species were lower in the Paleo group, associated with the reduced carbohydrate intake, which may have consequences for other chronic diseases over the long term.

Previous research has shown that diets high in fibre could play a role in preventing heart disease by promoting a healthy gut microbiome

Caveman Diet Excluded Foods
Paleo/Caveman Diet: Lack of whole grains implicated for heart-health risk

Genoni said the reason TMAO was so elevated in people on the Paleo diet appeared to be the lack of whole grains in their diet.

"We found the lack of whole grains were associated with TMAO levels, which may provide a link between the reduced risks of cardiovascular disease we see in populations with high intakes of whole grains," she said.

The researchers also found higher concentrations of the bacteria that produces TMAO in the Paleo group.

"The Paleo diet excludes all grains and we know that whole grains are a fantastic source of resistant starch and many other fermentable fibres that are vital to the health of your gut microbiome," Dr Genoni said.

"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.

"Additionally, the Paleo diet includes greater servings per day of red meat, which provides the precursor compounds to produce TMAO, and Paleo followers consumed twice the recommended level of saturated fats, which is cause for concern.

Glucose Intolerance and Weight Gain

Study from University of Melbourne, published in Nature journal Nutrition and Diabetes February 2016

blood sugar level chart
Glucose tolerance and weight gain were highlighted as issues in this study

Key Takeaways

  • Low Carb High Fat Diet (LCHF) exacerbated glucose intolerance
  • Following an LCHF diet for just eight weeks may lead to rapid weight gain and health complications

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.

The surprise findings prompted Lead author Associate Professor Sof Andrikopoulos to issue a warning about putting faith in so-called fad diets with little scientific evidence.

Andrikopoulos said 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.

In people with pre-diabetes or diabetes, the low-carb, high-fat (LCHF) diet could be particularly risky.

“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.”

The Study

Researchers at the University of Melbourne 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 researchers used mice for the study because their genetic, biological and behavioural characteristics closely resemble those of humans.


After eight weeks, the group on the LCHF gained 15% of their body weight, their glucose intolerance worsened and their insulin levels rose.

“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.”

Professor Andrikopoulos recommended the Mediterranean diet as the best for people with pre-diabetes or diabetes.

Professor Andrikopoulosexplains the key findings in this video:

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  • Genoni, A., Christophersen, C.T., Lo, J. et al (2019) Long-term Paleolithic diet is associated with lower resistant starch intake, different gut microbiota composition and increased serum TMAO concentrations. European Journal of Nutrition
  • Heart Statistics British Heart Foundation
  • B J Lamont, M F Waters & S Andrikopoulos (2016) A low-carbohydrate high-fat diet increases weight gain and does not improve glucose tolerance, insulin secretion or β-cell mass in NZO mice. Nutrition & Diabetes
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