How Safe Are Paleo Diets?

“Paleo,” or paleolithic diets — named after the ancient era when humans were still hunter-gatherers, before the development of agriculture — have seen a spike in interest in recent years. According to a recent article, “paleo diet” was the most searched-for type of diet on the Internet in 2014. Yet there is still confusion about what such a diet entails (hence the common reference to “paleo diets” in plural, rather than to one single diet), as well as uncertainty about how healthy such a diet is.

Many advocates of paleo diets see them as a good choice for people with diabetes or prediabetes, since they’re low in refined and easily digestible carbohydrates. Yet a recent study, published in the journal Nutrition & Diabetes, found that an approximation of a paleo diet had negative effects on metabolism in mice.


As described in an article on the study at Medical News Today, two groups of overweight mice with symptoms of prediabetes were followed for eight weeks. The first group was fed a diet designed to resemble a paleo diet, which was 60% fat and 20% carbohydrate. The second group followed its regular diet, which was only 3% fat. At the end of the eight weeks, the high-fat-diet mice had gained an average of 15% of their body weight, and they had higher levels of insulin and other markers of insulin resistance. Their average body-fat percentage also doubled, from about 2% to about 4%.

As the study’s authors point out, the weight gain seen in the high-fat-diet mice is equivalent to someone weighing 200 pounds gaining 30 pounds in less than two months. Such weight gain raises a person’s risk of developing prediabetes and Type 2 diabetes, high blood pressure, arthritis, and other disorders. The main lesson, they write, is that eating too much fat is unhealthy.

Yet this study has been attacked by a number of critics, for several different reasons. Perhaps its most obvious shortcoming is that it was conducted using laboratory mice, not humans. As one nutrition researcher writes in a letter to Nutrition & Diabetes, not only are ordinary mice not necessarily good stand-ins for humans, but the mice in this study — called New Zealand Obese mice — were bred to gain weight easily, especially in response to dietary fat. Moreover, the researcher writes, the mice in this study showed a response — worse blood glucose control despite lower carbohydrate in their diet — that is the opposite of the response humans have shown in several studies. For this reason among others, he writes, the study should be retracted by the journal.

Another criticism, raised by a prominent paleo-diet blogger, is that the feed the mice in the study were given to approximate a paleo diet was actually a terrible stand-in for the diet. As he notes, the mice’s feed contained very few whole foods, relying instead mostly on processed ingredients like casein (a protein found in milk), sucrose (table sugar), cellulose, and a number of vitamin and mineral supplements. Moreover, the only source of digestible carbohydrate in the mice’s diet was sugar, which is frowned upon in paleo diets. Their diet also contained canola oil, which also isn’t considered paleo-friendly by many of the diet’s advocates.

What’s your take on this latest study — do you think its findings in overweight mice hold any useful lessons for humans? Is it irresponsible for scientists to proclaim, after conducting a mouse-based study, that a certain diet is potentially harmful for humans? Have you tried — or are you interested in trying — following a paleo diet? If you’ve tried it, did you notice any positive or negative effects on your weight or blood glucose control? Leave a comment below!