Keto vs. paleo diet: which one is better? Experts weigh in

Those ubiquitous tips define two of the trendiest diets: keto and paleo. Their popularity stems from the weight loss success that people often see when they first go on the diets, which experts say is because of their restrictive nature. When you restrict your caloric intake in any way—in this case, specifically by limiting carbs—you are likely to see weight loss, says Federica Amati, head nutritionist at the U.K.-based health science company, Zoe, known for its at-home blood sugar and gut health test kit. 

But is one better than the other? Here’s how keto and paleo compare, and what experts think is best for overall health.

What is the keto diet?

Keto is a high-fat, high-protein, and low-carb diet dating back to the 1920s when it was first used to help control seizures in people with epilepsy, according to the National Library of Medicine.

“[Keto] does have science to support its use in specific brain diseases like children with severe epilepsy and schizophrenia,” Amati tells Fortune.

It is named for the concept of ketosis, a metabolic state where the body burns fat for energy instead of glucose, or carbs. That happens from severely limiting your carb intake, to the point where your glucose stores are so low that the body needs to rely on ketones—a byproduct of burning fat—for energy, according to the Cleveland Clinic. It can take anywhere from two days to over a week to reach ketosis.

Keto gained momentum as part of a low-carb weight loss trend, along with similar diets such as Atkins and Whole30. People on a keto diet will consume about 60% of their calories from fat, 30% from protein, and 10% from carbohydrates, according to the Cleveland Clinic. For someone eating 2,000 calories, that would be around 165 grams of fat, 40 grams of carbs, and 75 grams of protein. Foods on the keto diet include:

• Red meat, turkey, chicken, and fish
• Eggs
• Avocados, avocado oil, extra virgin olive oil, and coconut oil
• Butter and cream
• Nuts and seeds
• Low-carb vegetables like broccoli, spinach, kale, tomatoes, lettuce, and cucumbers
• Cheeses like cheddar, Parmesan, and goat cheese

What is the paleo diet?

The Paleo Diet, scientist Loren Cordain’s bestselling book published in 2001, popularized eating habits that mimic those from the Paleolithic Era, around 2.5 million to 10,000 years ago.

Cordain claims that contemporary changes in diet outpaced the human body’s ability to adapt—which he believes is a factor in the current pervasiveness of obesity, diabetes and heart disease. According to Cordain, the best approach is to return to what he believes our bodies were meant to eat as a means to stave off chronic metabolic illnesses.

According to the Mayo Clinic, foods allowed on the paleo diet include:

• Fruits
• Vegetables
• Nuts and seeds
• Eggs
• Lean meats, especially grass-fed animals or wild game
• Fish, especially those rich in omega-3 fatty acids, such as salmon and albacore tuna
• Oils from fruits and nuts, such as olive oil or walnut oil

But many foods are not allowed, as they were not around in the Paleolithic Era, including:

• Grains, such as wheat, oats, and barley
• Legumes, such as beans, lentils, peanuts
• Dairy products, such as milk and cheese
• Refined and added sugar
• Added salt
• Starchy vegetables, such as corn, jicama, peas and white potatoes
• Highly processed foods, such as chips or cookies

Amati says it is impossible to eat a true Paleolithic diet because food itself has changed so much—due to how we’ve changed the processing and farming of food and the evolution of plants.

How do they compare?

The biggest difference between keto and paleo is the types of foods you can eat. Keto is very strict in terms of your carbohydrate intake, which caps at around 40 to 50 grams of carbs. Paleo doesn’t have a specific limit on carbohydrates, however, and offers more room for more carbohydrates in the form of fruits and veggies.

On the other hand, paleo does eliminate dairy such as  milk, butter, and cheese, which are all staples of keto for their high fat and protein content.

Their ideologies are also vastly different. Paleo is supposed to be rooted in diets from thousands of years ago—before the advent of processed foods—while keto isn’t as particular about eating processed foods.

While keto and paleo have very different origins, they share quite a bit in common. Here are the main similarities.

Restrict carbohydrates

Although paleo doesn’t explicitly place a limit on the quantity of carbs you can eat per day, like keto does, the list of foods you can eat doesn’t contain many carbohydrates, namely whole grains, legumes, and starchy vegetables.

Both diets require a low percentage of carbohydrates as compared to the U.S. Dietary Guidelines’ recommendation of 45% to 65% of calories from carbs.

Short-term weight loss

A 2015 meta analysis of paleo diet studies observed that in the short-term—10 days to five weeks—participants experienced decreased waist circumference by an average of about one inch lost.

In the first six to 12 months of keto, researchers observed similar results of weight loss, but those effects seem to taper off after the 12-month mark. 

Weight loss on these diets is likely to occur very quickly, Amati says, because of the restrictive nature of the diets. Limiting food intake by cutting out the majority of carbohydrates will likely decrease overall calories—especially in the beginning, when your diet is changing the most—and naturally lead to weight loss.

May improve certain biomarkers

There is some evidence that keto and paleo can improve certain biomarkers in the short-term. The same 2015 meta analysis indicates that being on paleo can result in decreased triglycerides, lower blood pressure, and lower fasting blood sugar.

Similarly, research indicates that the keto diet can decrease blood pressure and triglycerides, and increase HDL (good) cholesterol.

However, both diets come with risks, especially when it comes to the long-term.

The risks of keto and paleo

Keto and paleo’s restriction of carbohydrates is one of the main aspects that experts find to be problematic with these diets.

“Carbs are the main energy source for the body,” Vanessa Rissetto, registered dietitian and founder of nutrition company Culina Health, tells Fortune. 

The U.S. Dietary Guidelines advises anyone above age two to eat roughly 45 to 65% of their calories from carbohydrates. Meanwhile, the FDA recommends that people consume no more than 275 grams of carbohydrates per day for a 2,000-calorie diet, which is roughly seven times more carbs than is allowed on the keto diet.

To keep carbs low, keto in particular limits how many vegetables and fruits you can eat, as well as whole grains and complex carbohydrates—which concerns Rissetto. 

“I lean more towards a varied diet,” Rissetto says.

People on keto will likely be lacking fiber, minerals, and micronutrients which impacts gut health, sleep, and energy—not to mention the potential overconsumption of red meat, which is a staple of keto, and is directly linked to colon cancer and other health issues, Rissetto says.

“Gut side effects could happen within a week [of being on the diets],” Amati says. That includes constipation, bloating, or general gut discomfort.

One major study from 2023 showed that the keto diet is linked to elevated levels of “bad” cholesterol in the body—which could double the risk of major cardiovascular health problems like artery blockages, heart attacks, and strokes.

Amati says anyone with an existing heart condition, heart disease, high cardiovascular risk, high colorectal cancer risk, or people with irritable bowel syndrome should stay away from these diets.

The Cleveland Clinic outlines the following potential adverse side effects of the keto diet:

• Nutrient deficiency
• Liver problems, from too much fat to metabolize
• Kidney problems, from too much protein to metabolize
• Constipation
• Brain fog and mood swings

“This is not a way to live our lives. It’s just not. It doesn’t work,” Rissetto says.

Paleo presents similar risks as keto—from high meat consumption and no whole grains, legumes, or starchy carbs—but Amati says it is slightly better than keto because there is more variation in the fruits and vegetables you can eat.

But the restrictive nature of both diets presents another concern: disordered eating patterns such as labeling foods as “good” or “bad” if they don’t fit the diet exactly, food obsession, and undereating from the restrictiveness of the diets, all of which could lead to diagnosable eating disorders. That is why Rissetto advises anyone with a history of disordered or restrictive eating, or an eating disorder, should stay far away from these diets.

Instead, both dietitians are in favor of a different approach when it comes to eating.

Which is better for you?

Amati and Rissetto agree that keto or paleo are only helpful as interventions for specific health reasons. Keto has long been used to treat children with epilepsy and people with certain mental disorders such as schizophrenia, for example.

They agree that people can try keto or paleo for temporary weight-loss—with the caveat that it is near impossible to keep the weight off after stopping such a restrictive diet—or for anyone looking to shift their diet away from processed foods. But neither think anyone should be on these diets in the long-term.

“They’re terrible for the environment and fairly unsustainable,” Amati says, pointing to the environmental impacts of eating such heavily animal-based diets and the overall difficulty in adhering to these diets.

Moreover, Amati and Rissetto believe that being on keto or paleo comes with potential risks to your health.

Diets for overall health

Like Rissetto, Amati believes that a varied diet—specifically one that is plant-forward—is going to be the best diet for anyone. The issue with both keto and paleo is how limiting and restrictive they are.

“To be in good health, you need a variety of food groups,” Amati says.

If you’re lost about where to start, Amati and Rissetto advise beginning with vegetables. Amati is a fan of filling half of your plate with your favorite veggies when you’re building a meal. Similarly, Rissetto says to add a cup of whatever vegetable you like to lunch and dinner, and then slowly build up variety from there as you try new vegetables in your meals.

While it can feel easier to follow the simple guidelines of keto and paleo—and listen to people on social media praising the diets—Amati says that what works for one person may not work for another, especially on risky diets like keto and paleo.

“Everyone should have a personalized nutrition approach,” Amati says.

If you do choose to try the keto or paleo diet, Rissetto advises to always do it with the help of a dietitian, never by yourself.

“Go talk to a dietitian and have them walk you through this and work with you so you can have longevity…and maybe some sustainability around it,” she says. Ideally, you’d make the diet less rigid, introducing more carbs to keto or paleo.

“Everyone is free to try what they want. I just would urge anyone who wants to try them to listen to their body,” Amati says. “If you start getting massive red signals, please listen.”

Still, Amati wants everyone to know: “These are not the diets to support your health.”

For more on nutrition:

• Learn how to try the keto diet with some of the best keto meal delivery services
• Your protein needs change as you get older. Here’s how much you should be eating at every age
• 3 ancient foods are the staple of this blue zone’s longevity diet