What’s the Difference Between the Keto and Atkins Diets?

If the most popular low-carb diets were ranked, the ketogenic or keto diet and the Atkins diet would be neck and neck. “They both follow carbohydrate restriction and focus more on protein and fat as energy sources,” says Megan Armstrong, RD, a clinical dietitian at Beaumont Health Weight Control Center in Canton, Michigan.

We’re not just talking about cutting back on the bad-for-you carbs — processed, high-sugar foods like donuts, cupcakes, and cookies — but also things like fruits and some veggies. The idea of limiting all carbohydrates so strictly is to put the body into ketosis, which means it begins burning fat instead of its usual fuel source, glucose (a kind of sugar). Carbs easily break down into glucose, so once those stores are depleted, your body has to burn fat.

Because both diets emphasize restricting carbs, you might think the keto diet and Atkins are basically the same. But there are important differences between the two. Here are some of the things you should know about each diet if you’re considering going low-carb.

How the Atkins Diet Works: An Overview

The Atkins diet was introduced in 1972 by a cardiologist named Robert Atkins, and it’s been popular on and off ever since. The original version of the diet (now called Atkins 20) has four phases. The introductory phase of the diet kicks it off with by far the most restrictive rules.

Protein and fat are fair game on Atkins, but carbs are strictly limited to between 20 and 25 grams (g) of net carbs (total carbs minus fiber) during the introductory phase. Those carbs come from nuts, seeds, veggies, and cheese. Your body will react to this change in carb intake quickly. If you're restricting carbs between 20 and 25 g per day and not overdoing it on protein, you will likely experience ketosis in the first phase, says Armstrong. Consuming too much protein can impair ketosis, however. You’ll stay in this phase until you’re about 15 pounds (lb) away from your goal weight.

Phase two doubles the daily carb allotment from 25 to 50 g, adding in foods like blueberries, cottage cheese, and yogurt. You’ll stay here until you’re about 10 lb away from your goal.

During the third phase, you’ll increase to between 50 and 80 g of net carbs as you try to find that perfect balance — how many carbs can you eat before the weight loss stalls? “It is done slowly, realistically, with some trial and error to see what amount of carbohydrates can be consumed again without causing any weight gain,” says Michelle Jaelin, RD, a blogger at NutritionArtist.com who is based in Hamilton, Ontario, Canada.

Once you figure that out and maintain it for one month, it’s on to phase four: lifetime maintenance. This part of the diet focuses on continuing the habits developed during phase three. Carbs are allowed (up to 100 g per day), as long as the weight doesn’t creep back up.

How the Ketogenic Diet Works: An Overview

In contrast to the multiphase approach of the Atkins diet, the ketogenic, or “keto,” diet, promotes one way of eating for the entirety of the diet. You’ll cut your carbs down to about 5 percent of your daily intake — so, for instance, in a 2,000-calorie-a-day diet, only 100 of those calories should come from carbs. Carbohydrates have around 4 calories per gram, which means you would need to limit yourself to 25 grams of carbs per day, about the amount in ¾ cup of cooked white rice, according to the U.S. Department of Agriculture (USDA). Seventy-five percent of your remaining calories will come from fat and 20 percent from protein. As a result of eating this way for a few days, you will enter ketosis, which you can monitor with keto urine strips if you choose.

This method of glucose fasting was first developed in the 1920s as a way to treat children with epilepsy, Armstrong says. There is a growing body of evidence that suggests the keto diet may help adults with epilepsy, too. One meta-analysis found that about 53 percent of patients with intractable epilepsy (epilepsy that cannot be controlled by medicine) who followed the keto diet reduced the frequency of their seizures by more than 50 percent. If you have epilepsy, be sure to check with your doctor before making any changes to your diet.

The keto diet really became popular when it was linked to weight loss, however. Many people without any history of seizures began to give keto a try — and research indicates that, at least initially, it can be useful for weight loss. An article published in Diabetes & Metabolic Syndrome: Clinical Research & Reviews found that subjects who followed the keto diet for 10 weeks had significant changes in weight, body fat percentage, and body mass index (BMI). That weight loss may be difficult to maintain, however. Past research found that while the keto diet does lead to more weight loss than a low-fat diet, weight loss generally peaks at the five-month mark and isn’t sustained after that.

Additionally, the ketogenic diet has some notorious side effects. “Headache, fatigue, and nausea are commonly reported side effects of ketosis due to the loss of water weight within the first few days to week,” Armstrong says. Collectively, these are sometimes called “the keto flu.”

Like other kinds of restrictive diets, keto can also lead to deficiencies in essential vitamins and minerals. Results of a review published in July 2021 in Frontiers in Nutrition found that even when people following a ketogenic diet consumed only nutrient-dense foods, they were still susceptible to fall short on fiber, vitamin K, linolenic acid, and water-soluble vitamins unless they took supplements.

The same review also found an association between long-term adherence to keto and an increased risk of heart disease. This may be due to the keto diet’s emphasis on fats, including saturated fats, which have long been associated with elevated risk of cardiovascular disease.

Still other research has found an association between keto and an increased risk of kidney stones, according to a systematic review and meta-analysis published in June 2021 in Diseases.

RELATED: What to Eat and Avoid on the Ketogenic Diet

Similarities Between the Keto and Atkins Diets

The keto and Atkins diets are both low-carb diets, and following them strictly will most likely lead to weight loss. Armstrong suspects you’ll mainly lose water weight in the beginning because carbs retain water. You may gain a lot of that back once you start eating normally again. “If ketosis is not maintained and carbs are added back in, fat burning slows and water weight is regained,” Armstrong says. Past research found that after one year, people who followed Atkins lost a modest amount of weight (4.6 to 10.3 lbs), though some of the weight was regained by the end of year two.

Neither diet requires counting calories, but you do need to track the number of carbs you take in. On keto, you also need to make sure you’re hitting the right percentages of calories coming from fat and protein.

Another thing these diets have in common is that both are fairly restrictive and difficult to stick with. U.S. News & World Report puts the Atkins diet’s “easy to follow” score at 2 out of 5 and keto’s at 1.9.

RELATED: Here’s What to Expect if You Try the Ketogenic Diet

A Look at the Differences Between the Keto and Atkins Diets

One key difference between the keto diet and Atkins is the amount of protein you’re allowed to take in. There’s no cap on Atkins, while keto limits protein to about 20 percent of your daily calories.

The other big difference is that keto centers on the body being in ketosis during the entire period of the diet, while ketosis plays a role only during phase one and possibly two of Atkins, and isn’t guaranteed depending on how much protein you’re getting. On Atkins, you eventually reintroduce carbs, but on keto, carbs are always limited.

That means Atkins may be more sustainable in the long run because it’s not quite as restrictive and doesn’t require you to make sure your body remains in ketosis. Plus, on Atkins, you can eventually add back nutritious foods like quinoa, oatmeal, and fruit, the Atkins website notes.

Which Low-Carb Diet Is Safer, According to Dietitians?

Jaelin says neither of these diets is recommended for people with diabetes, heart disease, or kidney disease. But without any of those chronic conditions, both diets can be safe if done for limited period, she says. Past research found that low-carb diets may be more effective than low-fat diets at lowering levels of triglycerides and A1C and raising levels of “good” HDL cholesterol.

The long-term safety of low-carb diets is a little iffy. Jaelin suspects that’s because dropout rates for studies involving low-carb diets are high. Past research found dropout rates for ketogenic diets to be as high as 84 percent.

Ultimately, the Atkins diet may be easier to stick with long-term because it allows you to gradually add carbohydrates back into your diet, and has been linked to fewer side effects than the keto diet. The keto diet was not created as a weight loss program, and thus is more restrictive and not as nutritionally balanced.

If you’re considering giving either of these diets a try, both Jaelin and Armstrong recommend speaking to a doctor or dietitian first.