• New research found that people who followed the paleo diet for a year had twice the amount of TMAO in their system.
• TMAO is a biomarker that previous studies have found increases a person’s risk for a major cardiovascular event by 62 percent and the risk of dying by 63 percent.
• A lack of whole grains is theorized to be the reason for the increased presence of TMAO. 
• Similar low-carb diets such as keto may similarly increase a person’s risk for heart disease. 

People who follow a paleo diet may have an increased risk for heart disease, a new study reports.

Researchers from Australia’s Edith Cowan University studied 44 paleo dieters and 47 people who followed a traditional Australian diet for one year.

Those who adhered to paleo had twice the amount of a biomarker that’s commonly associated with heart disease than the people who ate a typical diet.

The paleo, or “caveman,” diet, which followers believe resembles what human ancestors ate in the Paleolithic era 2.5 million to 10,000 years ago, relies heavily on meat, fish, vegetables, nuts, seeds, and some fruits. 

It excludes grains of any kind, dairy, legumes, refined sugar, processed oils, and salt.

A return to the food humans ate before modern farming techniques existed won’t only help them lose weight, paleodieters believe, it may also help them reduce their risk for some diseases related to many of the refined and processed foods abundant in today’s diets.

But for as popular as the paleo diet has been, little research has looked at the impact this style of eating has on long-term health, gut bacteria, and the microbiome. 

Indeed, the authors of this report, which was published in the European Journal of Nutrition, say it’s the first major study to look at just that — how a paleo diet can affect gut bacteria.

The investigators measured levels of trimethylamine-N-oxide (TMAO), an organic compound produced in the gut. Previous research has shown that TMAO is associated with an increased risk of heart disease.

A 2017 study found that TMAO increases a person’s risk for a major cardiovascular event by 62 percent and the risk of dying by 63 percent. 

The higher levels of TMAO and the bacteria that cause it (Hungatella) led the researchers to believe the paleo diet could increase a person’s risk for heart disease, a disease that kills 610,000 Americans Trusted Source each year.

“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 Angela Genoni, PhD, said in a statement. 

“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,” she said.

But it’s not just the increased amount of meat that many paleo dieters eat that Genoni says is likely responsible for the elevated risk of heart disease. 

Instead, she and the researchers point to what the dieters aren’t eating — specifically whole grains — for the potentially harmful issues.

Whole grains and the fiber gap

Whole grains are lauded for their bounty of fiber and nutrients, but whole grains aren’t on the menu for most paleodieters — or, for that matter, anyone following a low-carb diet, including the ketogenic (keto) diet.

“The paleo diet excludes all grains, and we know that whole grains are a fantastic source of resistant starch and many other fermentable fibers that are vital to the health of your gut microbiome,” Genoni said.

While fiber isn’t a flashy nutrient, it’s vitally important to health. 

Indeed, a diet that’s rich in fiber can promote better gastrointestinal (GI) health; reduce the risk for stroke, heart attack, obesity, and type 2 diabetes; and may reduce the risk of some cancers. 

It also keeps your GI tract moving to help you maintain regular bowel movements.

But Americans — and not just those on the paleo or keto diets — are chronically deficient in fiber. Only 5 percent Trusted Source of people in the United States meet the minimum fiber recommendations set forth by the Institute of Medicine.

Research suggests most people only get about 16 grams Trusted Source per day. But women should aim to get at least 25 grams of fiber per day. Men should aim for 38 grams.

This “fiber gap,” or the space between what’s considered optimal for health and what Americans are actually eating, is a focus of many healthcare providers and nutritionists. 

That’s because it may be one of the easiest ways to promote health and reduce disease and death risk.

In fact, a Lancet review Trusted Source of more than 240 studies and clinical trials found that transitioning people from a low-fiber diet (less than 15 grams per day) to a high-fiber diet (25 to 29 grams per day) could prevent 13 deaths and six cases of heart disease in every 1,000 people.

With the booming popularity of new diets that emphasize cutting carbs, even the healthy whole-grain ones, this new research points to possible concerns for heart health.

How to balance nutrient needs in all diets

Whole grains aren’t the only source of fiber. Fruits and vegetables also contain fiber, and not every one of them is marked off the lists of acceptable foods in keto and paleo plans.

But it’s the type of fiber that’s in the whole grains that concerns Rachel Fine, MS, RD, CSSD, CDN, owner of To The Pointe Nutrition, a nutrition counseling firm in New York City.

“The fact that paleo restricts whole grains is the biggest concern regarding inadequate fiber intake. Whole grains are particularly high in insoluble fiber, which, unlike soluble fiber — that coming primarily from veggies and fruit — helps to add bulk to stool. This plays a major role improving digestive regularity,” Fine said.

Some approaches to both keto and paleo diets emphasize leaner, healthier forms of protein and not red meat, which the researchers in this study point out was a major component of the study participants’ diet.

“This is why I developed Ketotarian, my plant-based ketogenic eating plan,” said Will Cole, IFMCP, DC, and author of “The Inflammation Spectrum.” “It focuses on healthy plant-based sources of fat instead of meat and dairy but allows for heart-healthy, wild-caught fish for pescatarians.”

“This way of eating also encourages more vegetable intake, as it is plant-based to get in essential fiber for a healthy gut,” he added. 

“Since some people do have sensitivities to legumes and grains, Ketotarian ensures you are still able to get in enough fiber through higher intake of vegetables, such as artichokes, broccoli, and Brussels sprouts,” Cole said.

Jedha Dening, a nutritionist, diabetes educator, and founder of Diabetes Meal Plans, says people following a keto or paleo diet should emphasize the fiber sources that are permitted.

“A person does not need to eat whole grains to obtain adequate fiber. This is a common misconception,” Dening said. 

“For instance, 1 cup brown rice contains about 3.5 grams of fiber; 1/2 avocado contains around 7 grams; and 1 cup of broccoli contains 2.4 grams. You can still obtain plenty of fiber when following a paleo or keto diet by including nonstarchy vegetables, nuts and seeds, and even lower-carb fruits.”

“The key is, people need to include higher-fiber foods in their diet and not just eat meat and cheese all day,” Dening continued. “Balance in the context of these diets is certainly the key.”

Fine, on the other hand, says these diets place too many restrictions on foods that research shows again and again are healthy.

“Restrictions of any kind are never advisable,” Fine said. “Diets that are highly restrictive, such as paleo, risk negative consequences. Restrictions result in a host of biological consequences that cause us to literally want what we think we ‘can’t have.’” 

“When we restrict carbs and/or fat, the body releases specific hormones to counter the restriction, promoting increased cravings of said macronutrients,” Fine said. 

“This is because our body relies on both carbs and fat for very specific metabolic functions,” she explained. “When one or both of these macros is not available from dietary restriction, the body will fight until you can no longer resist.”

Rather than extreme restrictions, Fine advises an “inclusive approach,” which she says is “key to long-term success” of any diet.

“Instead of rules, make choices. Add more minimally processed, nutrient-dense, plant-based foods, like fresh produce, nuts, seeds, and legumes to your meals. Psychologically, an inclusive approach allows for enjoyment of all foods,” Fine said.