Paleo diets are sold on two golden promises: low-carb eating and better gut health. But a new study from Australian researchers suggests that the two might not go hand in hand—cutting out the carbs might not work as advertised. Published in the European Journal of Nutrition, this study indicates that paleo participants have an abnormally high amount of Trimethylamine-N-oxide (that’s TMAO for short) in the gut, which could raise your risk of heart disease.
This new food fad, the paleolithic, paleo, or “caveman” diet, calls strictly for grass-fed meat, eggs, fish, nuts, berries, fruits, veggies, and natural sweeteners. Imagine what our early ancestors would have eaten hundreds of thousands of years ago, then remove the mammoth drives from the equation. The idea is to cut out artificial and factory-farmed foods and emphasize simple, effective nutrition.
The study followed 44 willing-and-ready paleo dieters as they adhered to the diet for a year. Half of them were strictly paleo: less than one serving of dairy and/or grains each day. The “pseudo-paleo” half was less regimented but still followed the basic diet. Both groups were measured against a control group consuming a standard Australian diet.
The results showed that the diet was not without its benefits: Paleo participants had a much higher vegetable intake than the control group, and they took in half as many carbs and just shy of a third of the starches.
Yet any low-carb diet will yield a lower total dietary fiber. Cutting out whole grains (and legumes, which the paleo diet does) means you have to look for fiber in fruits and vegetables instead, and the paleo dieters’ total fiber ultimately couldn’t match that of the control group.
But the low fiber was the least of the dieters’ problems: Paleo groups clocked up double the cholesterol of the control group, and their fat intake was significantly higher as well. The saturated fat levels among paleo groups was more than double the recommended Australian and international levels. Perhaps this is why many dietitians warn that you’re unlikely to lose weight on a paleo diet.
Gut health—tracked using blood and stool samples—was ultimately the goal of the study. Researchers found that consuming fewer carbs and more fats means less beneficial bacteria in the gut. Streamlining and simplifying your diet produces too few of the good bacteria and too many potentially harmful ones—including TMAO.
In the gut, TMAO production is linked to the bacteria Hungatella, itself connected to red meat consumption. Studies like a 2016 one from the Cleveland Clinic demonstrate that increased TMAO levels are biomarkers for higher risk of heart attack, stroke, and heart disease.
“The differences noted in microbiota composition associated with the high fat and low carbohydrate intake may not be beneficial for long-term health,” the study says. The researchers go on to say that according to their results, a strict paleo diet probably isn’t sustainable for long-term health.
The bright side is that while more Hungatella in the gut might enable other chronic diseases, the opposite is true as well: Eating less red meat and more whole grains helps heart health.
No diet is perfect—veganism makes it easy to stock up on the carbs and sugars. The Mediterranean diet has issues balancing its carbs with its proteins. The keto diet draws criticism for its high-fat, low-carb regime, not unlike the paleo diet.
The important takeaway is to research what you’ll be putting into your body and when. Don’t throw yourself headlong into a diet, no matter how many life-changing stories you’ve heard about it. Combating cardiovascular disease and living a healthier, better life means making more evolved choices about what you eat and how you eat it.