The Atkins diet is one of the best-known diets worldwide. It’s a low-carb, moderate-protein, high-fat diet.

Though Atkins has evolved to offer a variety of plans, the original version (now called Atkins 20) is still the most popular. It’s broken down into four phases, which are based on your daily net carb (total carbs minus fiber and sugar alcohols) allowance:

• Phase 1 (Induction). This phase allows for 20–25 grams of net carbs per day until you are 15 pounds (7 kg) from your goal weight.
• Phase 2. During this phase, you consume 25–50 grams of net carbs per day until you are 10 pounds (5 kg) from your goal weight.
• Phase 3. Your net carb allowance is raised to 50–80 grams per day until you have met your goal weight and maintained it for 1 month.
• Phase 4. During the final phase, you consume 80–100 grams of net carbs per day for ongoing weight maintenance.

As you approach your goal weight and advance through these phases, your daily carb allowance increases, allowing you to incorporate a greater variety of foods.

However, even during Phase 4, which allows for up to 100 grams of net carbs per day, you consume significantly fewer carbs than most people normally eat.

Most Americans get about 50% of their daily calories from carbs, which equates to about 250 grams of carbs if you eat 2,000 calories per day (1).

Summary Atkins is one of the most popular low-carb diets worldwide. It works in phases that allow you to gradually increase your carb intake as you progress toward your goal weight.

The keto, or ketogenic, diet is a very-low-carb, moderate-protein, high-fat diet plan.

It was first used to treat children who experienced seizures, but researchers discovered that it may benefit other people as well (2, 3).

The goal of the keto diet is to get your body into the metabolic state of ketosis, during which it uses fat rather than sugar from carbs as its main energy source (4).

In ketosis, your body runs on ketones, which are compounds that are formed upon the breakdown of the fat in your food or the fat stored in your body (5).

To achieve and maintain ketosis, most people need to limit their total carb intake to 20–50 grams per day. Macronutrient ranges for the keto diet are typically 5% of calories from carbs, 20% from protein, and 75% from fat (6).

Some people monitor their ketone production using blood, urine, or breath tests.

Summary On the keto diet, you restrict your total carb intake to less than 50 grams per day. This causes your body to enter ketosis and burn fat for energy.

Keto and Atkins share certain similarities but also differ greatly in some respects.

Similarities

As they’re both low-carb diets, Atkins and keto are alike in some ways.

In fact, Phase 1 (Induction) of the Atkins diet is similar to the keto diet, as it restricts net carbs to 25 grams per day. In doing so, your body likely enters ketosis and starts burning fat as its main source of fuel.

What’s more, both diets may result in weight loss by decreasing the number of calories you eat. Many carbs — particularly refined carbs like sweets, chips, and sugary drinks — are high in calories and may contribute to weight gain (7).

Both Atkins and keto require you to eliminate these high-calorie, carb-rich foods, which makes it easier to cut calories and lose weight.

Differences

Atkins and keto have certain differences as well.

While keto is a moderate-protein approach, with about 20% of calories coming from protein, the Atkins diet allows for up to 30% of calories from protein, depending on the phase.

Additionally, on the keto diet, you want to keep your body in ketosis by extremely limiting your carb intake.

On the other hand, the Atkins diet has you gradually increase your carb intake, which will eventually kick your body out of ketosis.

Due to this flexible carb limit, Atkins allows for a wider variety of foods, such as more fruits and vegetables and even some grains.

Overall, Atkins is a less restrictive approach, as you don’t have to monitor ketones or stick to certain macronutrient targets to stay in ketosis.

Summary Keto and Atkins are both low-carb diets that may aid weight loss by burning fat and cutting your calorie intake. However, on Atkins, you gradually increase your carb intake, while it remains very low on the keto diet.

Though once considered unhealthy, low-carb diets have now been shown to offer various health benefits.

Weight loss

Low-carb diets may result in more weight loss than other diet plans.

In a review of six popular diets, including Atkins, the Zone diet, the Ornish diet, and Jenny Craig, Atkins resulted in the most weight loss after six months (8).

A similar study found that Atkins was the most likely of 7 popular diets to result in meaningful weight loss 6–12 months after starting the plan. (9).

Though more restrictive than Atkins, the keto diet may aid weight loss as well. Research indicates that being in ketosis decreases appetite, thereby removing one of the biggest barriers to weight loss — constant hunger (4, 10, 11).

Ketogenic diets also preserve your muscle mass, meaning that most of the lost weight is more likely to be a result of fat loss (12, 13).

In one 12-month study, participants on a low-calorie keto diet lost about 44 pounds (20 kg) with few losses in muscle mass, compared to the standard low-calorie group, which only lost 15 pounds (7 kg) (12).

Additionally, ketogenic diets maintain your resting metabolic rate (RMR), or the number of calories you burn at rest, whereas other low-calorie diets may cause your RMR to decrease (13).

Blood sugar control

Research indicates that low-carb diets can benefit blood sugar control.

In fact, the American Diabetes Association recently revised the Standards of Medical Care, a document outlining how healthcare providers should manage and treat diabetes, to include low-carb diets as a safe and effective option for people with type 2 diabetes (14).

Low-carb diets have been shown to decrease the need for diabetes medications and improve levels of hemoglobin A1c (HgbA1c), a marker of long-term blood sugar control (15, 16, 17, 18).

One 24-week study in 14 obese adults with type 2 diabetes on the Atkins diet found that in addition to losing weight, participants lowered their HgbA1c levels and decreased their need for diabetes medications (18).

Another 12-month study in 34 overweight adults noted that participants on a keto diet had lower HgbA1c levels, experienced more weight loss, and were more likely to discontinue diabetes medications than those on a moderate-carb, low-fat diet (17).

Other benefits

Research suggests that low-carb, higher-fat diets may improve certain heart disease risk factors (19, 20, 21).

Low-carb diets may reduce triglyceride levels and increase HDL (good) cholesterol, thereby decreasing the ratio of triglycerides to HDL cholesterol (22, 23).

A high triglyceride-to-HDL ratio is an indicator of poor heart health and has been linked to increased heart disease risk (24, 25, 26, 27).

A review including over 1,300 people found that those on the Atkins diet had greater decreases in triglycerides and more significant increases in HDL cholesterol than individuals following a low-fat diet (22).

Low-carb diets have also been associated with other benefits, including improved mental health and digestion. Still, more research is needed (3, 28).

Summary Low-carb diets like keto and Atkins may result in more weight loss than other diet plans. They may also help you improve your blood sugar and decrease your risk of heart disease.

Both Atkins and keto have benefits and downsides.

The ketogenic diet is extremely restrictive and may be difficult to stick to. Limiting your protein intake to 20% of calories while maintaining a very low carb and a very high fat intake can be challenging, especially in the long term.

What’s more, some people may feel the need to monitor their ketone levels, which can be challenging and costly. Also, following a restrictive diet like the keto diet may lead to nutrient deficiencies if you don’t pay careful attention to your diet quality.

Additionally, evidence on the long-term safety or effectiveness of the keto diet is limited, so its long-term health risks are unknown.

Most people can reap several of the benefits of low-carb diets without being in ketosis. Therefore, moderate carb restriction on a low-carb diet like the Atkins diet — as opposed to a strict keto approach — is usually sufficient.

Overall, it’s most important to focus on choosing healthy foods, regardless of the ratio of protein, fats, and carbs you eat. For example, higher-carb diets rich in plant foods, such as vegetables and fruits, are known to benefit health in countless ways.

Though low-carb diets are healthy and safe for most people, it’s important to note that higher-carb diets that focus on whole foods are just as beneficial for health as low-carb, high-fat diets (29, 30, 31, 32, 33).

Your weight loss goals, overall health, and dietary preferences should all be taken into account when choosing the best eating pattern for yourself.

Summary Atkins is less restrictive than keto. Additionally, the long-term effects of the keto diet are not well known. Choosing healthy foods and limiting refined carbs is a great way to improve health, regardless of your carb intake.

Low-carb diets, particularly those focusing on high-quality, nutritious foods, can be very healthy.

Atkins and keto are both low-carb diets that may benefit weight loss, diabetes management, and heart health.

Their main difference is that you gradually increase your carb intake on Atkins, while it remains very low on the keto diet, allowing your body to stay in ketosis and burn ketones for energy.

Though some people may benefit from the more restrictive keto diet, a moderate carb restriction — like during the later phases of the Atkins diet — is sufficient for most to experience the benefits of a low-carb diet.