The Atkins 20 Diet

Medically Reviewed by Kathleen M. Zelman, RD, LD, MPH on February 09, 2021

• The Atkins 20 Diet: How It Works
• Atkins Diet Phases
• Science Behind the Theory
• Does It Really Work and Is It Safe?

The Atkins diet promotes weight loss through a low-carbohydrate diet. Backers of the Atkins diet say it can also prevent or improve many health conditions, including high blood pressure and heart disease.

WebMD takes a closer look at the Atkins diet and helps you decide if it is right for you.

The Atkins 20 Diet: How It Works

The Atkins diet has evolved since its creation in 1972. There are now two Atkins diets: Atkins 20 (the original diet, which is described here and is based on intake of 20 grams of Net Carbs) and the new Atkins 40, which is less strict (based on intake of 40 grams of Net Carbs).

The main features of the diet haven't changed: Lose weight and improve health by eating a low-carbohydrate diet that consists of:

• Protein
• Vegetables
• Healthy fat

The diet has an Atkins Food Guide Pyramid that helps explain the Atkins method. At the top of the pyramid are foods that you can eat a little of -- but only after you have lost weight. These include whole grains such as:

Missing from the Atkins Food Pyramid are "white" foods -- forbidden foods that you should avoid. These include:

• White sugar
• White rice
• White bread
• White potatoes
• Pasta made with white flour

You don't have to count calories on the Atkins diet as long as you are reasonable with portion sizes. The only thing you have to calculate are carbohydrates. Specifically you need to count Net Carbs -- the total grams of carbohydrates minus grams of fiber.

Atkins Diet Phases

The Atkins diet consists of phases. The amount of Net Carbs you eat each day varies based on the phase.

Phase 1 -- Induction. This is the strictest part of the diet. You must avoid all:

• Fruit
• Bread
• Grains
• Starchy vegetables
• Dairy products (except cheese and butter)
• Alcohol

You eat only 20 grams of Net Carbs daily. That's significantly less than the FDA recommendation of 300 grams of carbohydrates daily.

The goal of phase 1 is to rev up your body's ability to burn fat. And because you lose the most weight during this phase, it is designed to motivate you to stick with the diet.

Phase 2 -- Ongoing weight loss (OWL). During phase 2, you slowly add some whole food carbohydrates back to your diet, such as:

You can eat between 25 and 50 Net Carbs daily. Phase 2 lasts until you are about 10 pounds from your desired weight.

Phase 3 -- Pre-maintenance. During phase 3, you continue to add a variety of carbohydrates to your diet, including more:

• Fruits
• Starchy vegetables
• Whole grains

You can eat 50 to 80 Net Carbs daily. Phase 3 lasts for at least a month after reaching your desired weight.

Phase 4 -- Lifetime maintenance. Once you reach your ideal weight, you continue to eat a predominantly low-carbohydrate (80-100 Net Carbs per day) diet for life. By this time, you should have a good idea of how many carbohydrates you can eat to maintain your weight.

Science Behind the Theory

The main idea behind the Atkins diet is to change your metabolism so that you burn fat for energy instead of glucose, a process called ketosis.

When you eat foods high in carbohydrates, such as refined sugar, your body turns it into glucose. Your body can only store a certain amount of glucose. So it burns it off first, leaving fat to accumulate in the body.

The theory goes that if you significantly cut back on the amount of carbohydrates you eat, your body will spend more time burning fat and you will lose weight.

Not only does the Atkins diet change your metabolism, studies show that eating more protein helps to curb appetite.

Does It Really Work and Is It Safe?

Studies have shown that people who stick to a low-carbohydrate diet like Atkins can lose weight.

A study in The Journal of the American Medical Association comparing diets found that women on the Atkins diet lost more weight and experienced more health benefits. After one year on the Atkins diet, people in the study lost an average of 10 pounds. They also had improved triglyceride levels and lower blood pressure. But experts say any diet that helps you lose weight will probably improve your cholesterol.

Since most studies on the Atkins diet last a year or less, researchers don't know if the health benefits from the diet are maintained and if the diet is safe for long-term use. Some points to remember include:

• Many experts caution that eating a diet high in saturated fats can increase your risk of heart disease and cancer.
• A high protein diet can be harmful to those who have had previous kidney problems.
• And critics say the Atkins diet omits important nutrients such as vitamin C and potassium. People on the Atkins diet are encouraged to take an iron-free multivitamin and mineral supplement and an omega-3 supplement that contains fish oil.
• The Atkins diet also goes against dietary guidelines put out by many health organizations and medical professionals, including the American Heart Association, the American Dietetic Association, Dietary Guidelines for Americans, and the American Cancer Society. These groups recommend a diet with more whole grains, fruit, vegetables, and lower saturated fats.

Always check with your doctor before starting a weight loss program, especially if you have certain health problems or if you take medications.