The paleo diet: what science has to say

You’ve probably heard of the Paleo diet—it’s undoubtedly en vogue these days! You might have a friend or family member, maybe a work colleague, who raves about how great Paleo has been for their health or weight loss goals. But what does science have to say about the Paleo diet? Let’s take a look. 

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The Paleo diet—sometimes called the Paleolithic diet, caveman diet, hunter-gatherer diet, or Stone Age diet—is a dietary style intended to mirror the eating habits of our ancestors during the Paleolithic era. That means the typical Paleo diet meal plan includes lean meats and fish, fruits and vegetables, and nuts and seeds. 

There are variations of the Paleo diet. Some lean more plant-based, while others focus more heavily on animal products. The foundation is the same either way—it's about including foods our ancestors found through hunting and gathering.

All of this may sound like a fancy way to say followers of the Paleo diet cut out packaged or processed foods and snacks—but it’s a bit more complex than that. 

Farming emerged around 10,000 years ago, long after the Old Stone Age (the other name for the Paleolithic era). That means Paleo diet devotees also eschew grains (yes, even whole grains), dairy products, and legumes such as soy, lentils, and peanuts. Various styles of the Paleo diet include:

• Standard or strict Paleo—This form of the diet eliminates processed and refined foods, grains, soy, and dairy. Fruits and vegetables, as well as meat, fish, and dairy, are allowed without limitations. Nuts and seeds are okay in moderation.

• Autoimmune Paleo (AIP)—People with autoimmune conditions or chronic diseases such as Hashimoto's thyroiditis, Crohn's disease, rheumatoid arthritis, or systemic lupus erythematosus may feel that their symptoms are triggered by some foods traditionally allowed by the Paleo diet. Food triggers can include nightshade vegetables (peppers, tomatoes, eggplant), eggs, and nuts. This variation of the Paleo diet follows the basic guidelines but makes further restrictions by eliminating these trigger foods.

• Ketogenic Paleo or low-carb Paleo—A mashup of Paleo and keto, this diet follows the basic guidelines of Paleo. The difference is it aims to keep people in ketosis, a state of your body in which you're using fat instead of glucose as fuel. Though fruits and starchy vegetables are technically allowed, you'll eat them minimally to remain in a state of ketosis. People following this diet mainly eat "healthy" fats such as coconut oil, meat, and eggs, along with leafy green vegetables.

• Primal Paleo—This is essentially a more flexible version of Paleo. This diet has the same focus on unprocessed foods and staunchly avoids artificial sweeteners and gluten. Unlike normal Paleo, though, followers of this eating style may include some raw dairy and white rice in their diet.

Why all the restrictions? The foundation of the Paleo diet is the belief that our bodies are not suited for the modern diet. The theory is that our body can't process certain foods, which is responsible for many modern health problems, such as diabetes and cardiovascular disease (also called heart disease) (Klonoff, 2009).

So, does science support this idea that eating the way our ancestors supposedly did reduces your risk of numerous diseases? Research on the Paleo diet is limited since the diet hasn’t been around that long, but here’s what we know so far about the potential health benefits.

May improve glucose tolerance

A glucose tolerance test measures how quickly the body clears sugar from the blood and is commonly used as an assessment to gauge insulin resistance and diabetes. Participants in one small study who ate a Paleo diet for 12 weeks cleared sugar from their blood significantly faster than those who followed a Mediterranean diet for the same amount of time (Lindeberg, 2007).

Both groups showed an improvement in their glucose tolerance test results from their baseline at the beginning of the study. Paleo diet followers saw the most significant changes, though. Everyone involved in the study had either high blood sugar and heart disease or type 2 diabetes at the start of the study. By the end of the study, every participant in the Paleo group had achieved normal blood sugar levels, whereas only about half of those in the Mediterranean group had (Lindeberg, 2007).

Participants of another small study on nonobese sedentary people also saw improvements in glucose tolerance. Researchers aimed to ensure the changes weren't due to weight loss, so the participants weighed themselves daily to ensure their weight was stable throughout the study. A Paleo diet style of eating improved their glucose tolerance after just 10 days (Frassetto, 2015).

May help you lose weight 

Several studies have found that the Paleo diet may help some people lose weight. 

Participants in the Lindeberg study all lost weight, with Paleo eaters losing an average of 11 pounds compared to the average 8.4 pounds lost by those in the Mediterranean diet group. Neither group restricted calories (Lindeberg, 2007).

Other studies have found the same when it comes to weight loss. 

Participants in one small study who followed the Paleo diet for three weeks lost an average of 2.3 kg (about five pounds) (Österdahl, 2007). Short-term weight loss has also been seen by a review of clinical trials and a comparison of four fad diets, which found that the Paleo diet led to participants eating less, resulting in weight loss (Manheimer, 2015; Obert, 2017). 

It is worth noting, though, that there haven't yet been long-term studies on the effects of the Paleo diet on weight. So, we don't know if participants maintained their initial weight loss by following this eating style. No matter what diet you're following, weight loss results as long as the number of calories you're consuming is less than the number of calories you're burning.

May help control blood pressure

Systolic blood pressure is the pressure inside your blood vessels when your heart is squeezing. Diastolic blood pressure is the pressure inside your blood vessels when the heart is relaxed. High systolic blood pressure may be more indicative of your risk of potential heart problems such as a heart attack or stroke than diastolic blood pressure (Blood Pressure Association U.K., n.d.). 

Although quite small, the Österdahl study found that after just three weeks, participants following the Paleo diet had improved their systolic blood pressure by three points (Österdahl, 2007). Another study found that three months on the diet successfully lowered diastolic blood pressure in participants with type 2 diabetes (Jönsson, 2009). It’s important to note that these were small decreases, and it’s unclear if they led to long-term health improvements for the participants of these studies.

May lower triglycerides

The potential benefits for your heart health don’t end there, though. 

Triglycerides are a type of fat or lipid found in your blood that may affect your arteries. High triglyceride levels may increase your risk of stroke and heart disease by contributing to the hardening of arteries or the thickening of artery walls (NIH, n.d.). 

Multiple studies have found that going Paleo may help lower your triglyceride levels. Triglyceride levels have improved in studies that looked at nonobese sedentary people, those with type 2 diabetes, and people with hypercholesterolemia (high cholesterol levels) (Frassetto, 2015; Jönsson, 2009; Pastore, 2015). Even though triglyceride levels improved, it’s unclear if this led to long-term benefits for the study participants.

May reduce inflammation

Here's where some debate starts. It's not clear if inflammation benefits come specifically from Paleo, or if they just come from eliminating processed foods.

Many ingredients in modern processed foods are known to cause at least low-grade inflammation. One example of this is omega-6 fatty acids that we get through vegetable oils such as soy and canola oil. Past research has found that diets with high omega-6 and low omega-3 intake (considered a “good” fat) may cause chronic inflammation (Manheimer, 2015). But, again, this is not a quality unique to a Paleo lifestyle. You could eliminate these foods and ingredients without following all of the restrictions put in place by this diet.

Offers a large community

Although certainly not quantifiable, one of the biggest benefits of the Paleo diet is the large community that has formed around this eating style.

There are many forums online where people can ask for help, and blogs replete with Paleo recipes. Some websites specialize in troubleshooting common concerns followers of the popular diet may have along the way.

These resources may make it easier to follow this diet, making it more likely to reap benefits than you might on a diet you follow on your own. Although research hasn't been done on these support materials and the Paleo diet specifically, social support was found to be one factor that increased diet adherence in a meta-analysis that looked at 27 clinical trials (Lemstra, 2016).

Exact Paleo meal plans look different depending on which type of Paleo lifestyle you choose to follow. For the examples below, however, we'll stick to the standard or "strict" Paleo diet since it's the core eating plan from which the variations make small changes.

What to eat

• Vegetables: Broccoli, carrots, cauliflower, onion, peppers, tomato

• Fruits: Apples, avocados, bananas, oranges, pears, raspberries, strawberries

• Nuts and seeds: Almonds, cashews, macadamia nuts, pumpkin seeds, sunflower seeds, walnuts

• Meats: Grass-fed beef, chicken, lamb, pork, turkey

• Fish and seafood: Wild-caught fish such as salmon and tuna, shrimp

• Eggs: Ideally, choose eggs from pastured, free-range chickens.

• Fats: Avocado oil, coconut oil, extra-virgin olive oil

What to avoid

• Grains: Bread, pasta, and whole grains such as barley, spelt, rye, and wheat

• Dairy: Most plans have you avoid all dairy, though some include full-fat versions.

• Legumes: Soy, soy products, lentils, chickpeas, beans, and peanuts

• Processed foods: This includes any products made with artificial sweeteners, high-fructose corn syrup, trans fats, and many vegetable oils, such as canola, soybean, and safflower oils.

• Refined sugar: High-fructose corn syrup and white sugar (and any products made with these ingredients)

• Tubers: White potatoes

When you go Paleo, you give up anything that wasn’t around before farming was developed. This may require research on your part since the distinctions aren’t always clear. Sweet potatoes, for example, are approved on a Paleo eating plan but white potatoes are not.

You probably already guessed the biggest problem with the Paleo diet from a practical perspective: It can get really restrictive. 

That means it may be hard for you to sustain the Paleo lifestyle long-term, though leaning on resources such as blogs for Paleo recipes and forums for getting questions answered may help. 

It can also get expensive, depending on how you format your eating plan. Although Paleo replacements for off-limit foods such as tortillas and bread do exist, they’re far pricier than their normal counterparts. But if you’re fine forgoing these replacements, it may bring the cost of this style of eating down.

There’s also a lot of debate about the complete removal of grains from the diet. Grains, especially whole grains, are still considered a healthy food group by many nutrition experts and researchers. Thanks to their high fiber content, they’ve been shown in numerous past studies to support weight management and gastrointestinal health (Jonnalagadda, 2011). 

Finally, it’s almost impossible for vegetarians and vegans to follow this style of eating since many sources of plant-based protein—including soy (tofu, tempeh), beans, and wheat (seitan)—are all excluded on this diet.

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Current version

August 13, 2020

Written by

Linnea Zielinski

Fact checked by

Mike Bohl, MD, MPH, ALM

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About the medical reviewer

Mike Bohl, MD, MPH, ALM

Dr. Mike is a licensed physician and a former Director, Medical Content & Education at Ro.