Paleo Diet vs. Keto Diet: What's the Difference?

More than 70% of Americans are overweight or obese, and because of our collective weight problem, many of us are looking to shed excess pounds. While there's no shortage of diets and approaches to losing weight, two that have gained a following in recent years are the paleo diet and the keto (short for ketogenic) diet. Both of these diets emphasize boosting fat intake and minimizing carbohydrates, adding up to rapid weight loss. But there's some nuance between the two that you should know about before trying either diet.

Paleo Diet Overview

"The paleo diet is an elimination diet based on the research of Dr. Loren Cordain," says Nina Young, wellness education specialist at Facey Medical Foundation in Mission Hill, California. "It eliminates foods that were not eaten by our paleolithic ancestors before farming began 10,000 years ago. The paleo philosophy is based on the 'evolutionary discordance hypothesis,' the idea that getting away from the eating and activity habits of our ancestors creates a mismatch between genes and lifestyle, contributing to the rise of chronic health problems we see today."

The idea is simple: If our paleolithic ancestors didn't eat it, we shouldn't either. This translates into a focus on whole foods, fruits and non-starchy vegetables that are in season (think leafy greens and cruciferous veggies like broccoli and cauliflower), plus plenty of meat. Anything that requires intensive farming is out, so that means cutting out beans and legumes, rice and other cultivated grains, as well as dairy. Alcohol is also out, as it's a grain-based product that's high in carbohydrates. White potatoes are out as they're too starchy, but sweet potatoes are generally considered OK to include in a paleo diet, as many hunter-gatherer societies feature these root veggies as a staple.

The idea of eating in tune with our biological ancestry has been around since the 1970s, but the diet gained in popularity in the 2000s with the development of CrossFit, an exercise regimen that espoused this dietary plan to fuel sports performance and the ideal body. Today, many food companies offer paleo-friendly products that make keeping paleo a somewhat more convenient proposition.

[SEE: Fruits to Eat on a Low-Carb Diet.]

Keto Diet Overview

The keto diet leverages the body's innate ability to burn fat to fuel activity and weight loss by drastically cutting carbohydrates and increasing the ratio of good fats in the diet. "The keto diet has been used to treat drug-resistant epilepsy for the past 100 years," Young says. "But it has increasingly been used as a weight-loss diet. It takes advantage of our body's ability to tap into fat stores, like fasting does. This low-carb, high-fat diet is meant to induce ketosis by adjusting macronutrients," or fat, carbs and protein.

Keto diets force the body to use fat as its primary source of energy, an approach that revolves around a biochemical process called ketosis. Ketosis is when your body breaks down both dietary and stored fat for fuel and creates ketones in the process. Ketones are a byproduct of burning fat that are generated in the liver that a can be measured in the blood. If you're going to be strict about the keto diet, you'll likely be testing your blood regularly to track the level of ketones to make sure you're in the target zone for fat burning.

The keto diet was initially developed in the 1920s as a means of treating severe epilepsy in children. This diet was composed of 90% fat, 6% protein and 4% carbohydrates, which helped to quell epileptic seizures. The diet is still used today in people for whom other treatments haven't been successful.

Though classic keto cuts out almost all carbs, there are other, modified versions of the diet that some people use today. Liz Weinandy, a registered dietitian with the Ohio State University Wexner Medical Center, says that the "modified keto diet is 82% fat, 12% protein and 6% carbs. It's very similar to a classic keto diet," but is slightly less extreme in its reliance on fat as the primary source of calories and thus may be marginally easier to stick with longer term.

In either the classic or modified keto approach, the high-fat/very-low-carb ratios can be challenging for most people to achieve in day-to-day life, and as such it may be better to use short-term to cut weight quickly or to cycle in and out of from time to time rather than being a lifestyle approach.

[SEE: What Are Low-Carb, High-Fat Diets? Are They Healthy?]

Health Benefits

Paleo Diet
The paleo diet can be a good way for people to lose weight quickly, because eliminating processed foods, sugars and carbohydrates can jump-start a weight loss program. If the focus is on adding unprocessed foods, with lots of vegetables, it can be a healthy alternative to the standard American diet. Because being overweight or obese is associated with a higher incidence of type 2 diabetes, the paleo diet may be a good option for reducing that risk.

"By cutting down on refined carbohydrates and highly processed foods, these diets tend to lead to weight loss and better blood sugar control without the feelings of deprivation and constant counting that usually come with traditional diets," Young says.

Keto
Transitioning to a classic keto diet can lead to rapid weight loss. Going keto can also help reduce food cravings and appetite and because the keto diet features plenty of fat, you may feel less hungry when dieting and consume fewer calories. However, for many people who try the keto diet, staying on it long-term can be immensely challenging because it's so restrictive.

Some research has also indicated that the keto diet can improve hormone balance in some individuals, with less acne and reduction of symptoms associated with polycystic ovary syndromein some women.

Studies are also ongoing into whether or not a ketogenic diet can slow the growth of cancer or reduce the risk of cancer recurrence. The idea is that many types of cancer cells thrive when growing in a high-sugar environment, so by depriving the body of sugar and forcing it to switch to fat-burning, that could slow down the growth of cancer or potentially shrink tumors. Some researchers say that the diet could eventually be considered a form of treatment for certain kinds of cancers when used in conjunction with chemotherapy and other treatments, but definitive answers are still forthcoming.

There have also been some indications that the diet may be able to help with diabetes management, but long-term data is still limited.

Health Risks

Paleo
Because the diet eliminates grains, that can potentially lead to a reduction in the overall amount of fiber and other important nutrients in your diet. Fiber is important because it can help your digestive tract work better -- moving wastes along and feeding the good bacteria in your gut. Because fiber intake could be reduced on the paleo diet, it could change the gut microbiome, an area of health we're still learning about. As our understanding grows, that may alter how we look at certain diets and their health impacts.

In addition, if you add lots of fatty cuts of meat to your diet, that could actually increase your risk of heart disease or certain types of cancer. A 2015 report from the WHO found that processed meats, such as bacon and lunch meat, can elevate risk for colorectal cancer. Therefore, it's important to choose lean meats that have been minimally processed if you're switching to the paleo diet. And Young adds that "eating large amounts of animal protein can lead to gout, high cholesterol and kidney stones."

Keto
A common complaint among people who have recently switched to a keto diet is the so-called keto flu. Symptoms include:

-- Fatigue.

-- Headaches.

-- Muscle aches.

-- Gastrointestinal distress.

It usually passes within a few days and is a sign that your body is switching to burning fat. During the week or so that people commonly experience this keto flu, it can be tough to keep up athletic performance and feel normal. Getting plenty of sleep and hydrating well can help you get over the keto flu a little faster.

Young says that the keto diet can also lead to " electrolyte imbalances, increased cholesterol and constipation. This is why I recommend working with a dietitian to minimize these risks."

Because the keto diet is restrictive, anyone who has or has dealt with an eating disorder should skip it. Children and women who are pregnant or nursing should also avoid the keto diet. And those with kidney disease should exercise caution and get supervision before adopting this diet.

Weinandy adds that because it can impact how the body uses glucose, "people who have blood sugar issues should be cautious." Diabetics may also want to avoid the keto diet, or follow it only under the close supervision of a doctor or a dietitian with special training in diabetes management. Those who are underweight or malnourished should also exercise caution, as the diet can trigger weight loss.

Shawn Wells, a registered dietitian and certified sports nutritionist based in Dallas-Fort Worth, says that for some people following the keto diet, they get too caught up in tracking macronutrient ratios and don't spend enough energy looking for high-quality food. So these individuals "tend to eat poor-quality, processed fats, which will show results in the short term but can lead to serious health issues in the long term. This is called 'dirty keto' and should be avoided." If you're relying on processed meat products and artificial sweeteners, you should take a step back and reassess your diet. "Keto diets should be focused on whole food sources to ensure that the large amount of fats are coming from natural, undamaged sources," he explains.

[See: 15 Best Weight-Loss Diets at a Glance.]

Costs

The costs for following either the paleo diet or the keto diet are likely to be similar. "The paleo diet and clean version of the keto diet encourage wild-caught fish, pastured poultry and grass-fed beef," Young says. "Choosing to buy these sustainable proteins or organic produce would make either diet more expensive" than a standard carb-heavy diet that may feature cheaper food items such as white pasta and grains.

Which Is Better?

For fast weight loss, both diets offer a similar proposition. Longer-term maintenance of weight loss and sticking to either diet as a lifestyle can be challenging for many people.

In U.S. News' 2020 Best Diet rankings, the paleo diet tied for No. 29 overall out of 35 diets. For weight loss, it tied for 23rd place. The keto diet ranked 34th overall. For weight loss, it did a lot better, tying for 3rd place in the Best Weight-Loss Diets category. Weinandy says that while weight loss is a common outcome for people who adopt the keto diet, "I do sometimes see people gain weight on the keto diet because they're eating so much fat."

Wells says that he tends to recommend the keto approach to clients, but emphasizes that you should focus on a clean, whole foods version of the diet rather than processed or pre-packaged foods. He also prefers a phased or cyclical approach to keto. "As you become more in tune with your nutrition and achieve some weight loss goals, you can become more flexible and add foods back in -- in phases."

For some people, the paleo diet may be easier to stick with because it's a little less restrictive. "While many carbs are restricted on the paleo diet, it is not necessarily low-carb," Yougn says. Although the keto diet can include some foods that are eliminated on the paleo diet, such as dairy and soy.

As such, "the paleo diet is more likely to be sustainable long-term and have fewer side effects," Young says. I typically recommend following the keto diet short term and then transitioning to a more sustainable diet. If you are thinking about trying either one, I suggest talking with a dietitian to see whether it would be healthy for you."

And, she adds "if you try one of these diets and feel great, know that you don't have to follow it 100% for the rest of your life to feel benefits. Perhaps you learned that you feel better eating fewer carbs, meal prepping or having less junk food. You can use this information to understand what works best for you, treating the diet like a template to help you create your own personalized plan."