Atkins Diet: The Ultimate Guide

The ketogenic diet may be the “it” low-carb diet for weight loss right now, but its predecessor, the Atkins diet, is the original version of this restrictive eating approach. “Atkins and keto are both low-carb diets that may benefit weight loss, diabetes management, and heart health,” says Vanessa Rissetto, RD, a nutritionist based in Hoboken, New Jersey.

In addition to keto being much higher in fat than Atkins, a main difference between Atkins and keto is that you gradually increase your carb intake on Atkins, Rissetto says. Meanwhile, she adds, carbs “remain very low on the keto diet, allowing your body to stay in ketosis and burn ketones for energy.”

Today, the diet, also called the Atkins Nutritional Approach, comes in three versions. (1)

Atkins 20 is for people who:

• Want to lose more than 40 pounds (lb)
• Have a waist circumference of over 35 inches (women) or 40 inches (men)
• Have prediabetes or type 2 diabetes

Atkins 40 is for people who:

• Want to lose fewer than 40 lb
• Are pregnant or breastfeeding
• Require a diet with a wider variety of foods

Atkins 100 is for people who:

• Want to maintain their current weight
• Are pregnant
• Are breastfeeding and trying to maintain their weight

Before trying any version of the Atkins diet — and especially if you are pregnant and considering any Atkins plan — check with your healthcare team.

All forms of the Atkins diet are focused on restricting what are called net carbs (including those in veggies) and emphasize eating protein and healthy types of fat. Select carbs are added back to your diet as you start approaching your weight loss goal.

Atkins defines net carbs as grams of carbs minus grams of fiber and grams of sugar alcohols. (Note that the U.S. Food and Drug Administration [FDA] does not recognize “net carbs” as an accepted nutritional term.) (2)

Atkins 20 and Atkins 40 involve various phases, while Atkins 100 is considered a lifestyle approach and calls for consuming no more than 100 net carbs per day. In Atkins 20, your initial, “induction” phase limits you to 20 grams (g) of net carbohydrates, while in Atkins 40, your induction phase limits you to 40 g of net carbohydrates, which gives you a little more flexibility in the foods you can eat in the beginning (including, for example, select fruits). (1) In Atkins 20, you add net carbs back to your diet in 5 g increments (20, 25, 30, and so on), while in Atkins 40, you add net carbs back to your diet in 10 g increments, explains Lauren Popeck, RD, of Orlando Health in Florida.

Atkins 20 Foods

To help jump-start your weight loss on the Atkins 20, you might consume some of the following foods:

• Foundation veggies, such as broccoli, spinach, bok choy, and cucumbers
• Protein, like eggs, chicken, and beef
• All fish, including salmon, cod, flounder, and herring
• Butter and olive oil
• Some cheeses, such as cheddar, goat, Swiss, and Parmesan

You can find a full, comprehensive food list for phase one of the Atkins 20 on the Atkins website. (3)

Atkins 40 Foods

If you’re following the Atkins 40 plan, you can eat all of the above, as well as the following foods (so long as you keep net carbs under 40 g per day): (4)

• Nuts and seeds
• Legumes (beans)
• Fruit
• Starchy vegetables, like squash, potatoes, and beets
• Whole grains, like barley, whole-grain rice, and whole-wheat pasta

Atkins 100 Foods

Atkins 100 followers can eat virtually all foods, so long as you do not exceed 100 g of net carbs per day. Carbs can add up fast if you’re eating sugar or refined carbs, so it’s best to limit or avoid those. (1)

The entire Atkins diet is available for free online.

The premise of the Atkins diet is that if you count and limit carbs — the body’s usual fuel — your body will be forced to burn your fat stores for energy, thereby promoting weight loss. As with many other fad diets, the main idea is to stop eating foods made with refined flour and sugar. But if you’re trying to follow the Atkins 20, even carb-dense whole-grain foods are on the don’t-eat list until you reach the maintenance phase.

“Cutting out carbs can contribute to weight loss initially. However, eliminating whole food groups, such as grains, milk, yogurt, and fruit, is likely unsustainable and inadequate in nutrients,” Popeck cautions. “Fiber will certainly be lacking, as well as calcium, potassium, and other vitamins and minerals.” (More on this in the cons section.)

RELATED: What Is an Elimination or Exclusion Diet?

The Atkins 20 and Atkins 40 versions of the diet are divided into different phases.

Phase 1

The first phase, induction, can last from as little as two weeks to many months, depending on your goals.

Phase 2

The next phase, which focuses on ongoing weight loss, allows you to gradually increase your daily carb total.

Atkins 20 During phase 2 of Atkins 20, you’ll add more net carbs in 5 g increments and add variety to your diet with antioxidant-rich berries, some nuts and seeds, and more vegetables.

(In the Atkins 20 plan, there are technically two phases here: phase 2 and phase 3, with phase 3 starting once you’re within 10 lb of your goal weight. Both phases focus on adding carbs back into your diet while you continue to lose weight.)

Atkins 40 During phase 2 of this plan, you add more carbs in 10 g increments primarily by increasing your portion sizes. The diet recommends moving into this phase when you are within 10 lb of your goal weight.

You can keep increasing carbs on both plans until you see weight loss slow or stop. At that point, depending on how close you are to your desired weight, you can move on to weight maintenance or cut back on carbohydrates if weight loss has slowed too much. Because protein and fats are more filling than refined carbs, the idea is you will actually tend to eat less quantity-wise, yet feel full at each stage.

Phase 3

The final phase, which you start when you’ve reached your goal weight and have maintained it for at least a month, is a lifetime weight-maintenance plan, keeping daily net carbs to about 80 to 100 g.

All plans recommend avoiding sugar and refined carbs, Popeck explains. In addition, here are some of the main foods you’ll be tasked with eating and avoiding on each plan:

Atkins 20 food list (5)

• Eat: foundation vegetables like spinach, cauliflower, broccoli, and more; healthy fats like olive oil and butter; nuts and seeds; and most cheeses
• Avoid: fruits like pineapples and mangoes; starchy vegetables, like potatoes; and grains, at least initially

Atkins 40 and Atkins 100 food list (1,4)

• Eat: all the foods recommended for Atkins 20, along with fruits like cherries, berries, and melons; legumes; some starchy vegetables, like squash and potatoes; and whole grains
• Avoid: white or processed carbs, like white bread or pretzels, and hidden sources of sugar

Yes, it is possible for vegetarians and vegans to follow the Atkins diet, though meeting protein goals will be more difficult since many go-to protein sources — such as fish and meat (and dairy for vegans) — are off-limits.

Knowing this, researchers in Toronto developed the Eco Atkins diet. (6) It calls for 31 percent of calories to come from protein (soy protein, nuts, and veggie burgers for vegans, and eggs, cheese, and tofu for vegetarians), 43 percent from fat (olive oil, avocado, and nuts), and 26 percent from carbohydrates (fruits, vegetables, and whole grains).

A study published in 2014 found that participants lost about 15 lb after six months on the vegan version of the Eco Atkins diet. (7)

Vegans and vegetarians on the Atkins diet should also take a multivitamin and a fish oil supplement (or flax oil for vegans) to ensure they’re getting proper amounts of nutrients. It’s also recommended that those on the Eco Atkins version of the diet jump right into Atkins 20 phase 2 or Atkins 40 since the induction phase can be very difficult. (6)

Your weekly menu will differ depending on which Atkins plan you’re following.

Atkins 20

Here’s how a week of eating on the Atkins 20 diet might look. (8)

Day 1

• Breakfast Cheese and spinach omelet with avocado and salsa
• Lunch Roast chicken stir-fry
• Snack Mozzarella string cheese
• Dinner Chicken and broccoli Alfredo and a salad

Day 2

• Breakfast Scrambled eggs with sautéed onions and cheddar cheese
• Lunch Taco bowl with beef, ½ an avocado, mixed greens, tomato, onions, and green peppers
• Snacks Atkins Caramel Chocolate Nut Roll Bar; Muffin in a Minute
• Dinner Fish with artichoke sauce, cauliflower, and a spinach salad

Day 3

• Breakfast Tomato, Avocado, Spinach, and Monterey Jack Stacks
• Lunch Atkins Frozen Orange Chicken
• Snacks Atkins Milk Chocolate Delight Shake; 2 stalks celery with 2 tablespoons (tbsp) cream cheese
• Dinner Stuffed Pork Chops With Fonduta and Fennel Gratinata and broccoli

Day 4

• Breakfast Red bell pepper stuffed with eggs and spinach
• Lunch Atkins Chocolate Peanut Butter Bar
• Snacks 1 cup sliced cucumber with 2 tbsp green goddess dressing; Atkins French Vanilla Shake
• Dinner Atkins Frozen Crustless Chicken Pot Pie with ½ cup Brussels sprouts and 1 tbsp olive oil

Day 5

• Breakfast Atkins Frozen Ham and Cheese Omelet
• Lunch Atkins Frozen Chili Con Carne with 2 cups mixed greens and 2 tbsp Italian dressing
• Snacks 1 cup sliced red bell pepper with 2 tbsp ranch dressing; Atkins Strawberry Shake
• Dinner Chicken Chorizo and Cauliflower Sauté With Cheese and Sausage

Day 6

• Breakfast Beef sautéed with peppers and onions and topped with cheese
• Lunch Atkins Creamy Chocolate Shake
• Snacks Atkins Caramel Chocolate Peanut Nougat Bar; 5 snap peas with 2 ounces (oz) of cheddar
• Dinner Atkins Frozen Beef Merlot

Day 7

• Breakfast Atkins Chocolate Almond Caramel Bar
• Lunch Cobb salad
• Snacks 2 celery stalks with 2 oz cheddar; ½ cup chopped red bell pepper with 2 tbsp ranch dressing
• Dinner Atkins Frozen Meatloaf With Portobello Mushroom Gravy

Atkins 40

Here’s how a week of eating on the Atkins 40 diet might look. (2,9)

Day 1

• Breakfast Cheese and spinach omelet with avocado and salsa and a slice of whole-grain toast
• Lunch Roast chicken stir-fry
• Snack Handful of walnuts or ¼ cup of blueberries
• Dinner Chicken and broccoli Alfredo and a salad

Day 2

• Breakfast Chicken chorizo with cauliflower sauté, cheese, and salsa
• Lunch Chicken over baby kale Caesar salad
• Snacks Atkins Milk Chocolate Delight Shake; ½ small banana with 2 tbsp peanut butter
• Dinner 6 oz salmon with ¼ cup wild rice, 2 cups mixed greens, and ½ cup sliced cucumbers

Day 3

• Breakfast Atkins Plus Vanilla Shake
• Lunch Atkins Frozen Shrimp Scampi with 2 cups mixed greens, 1 small tomato, ½ avocado, and 2 tbsp Caesar dressing
• Snacks 1 carrot with ¼ cup hummus; ½ cup blackberries with ½ cup Greek yogurt
• Dinner Chimichurri Steak and Cauliflower Mash

Day 4

• Breakfast Oatmeal topped with ¼ cup chopped pecans and ¼ cup sliced strawberries
• Lunch 5 oz hamburger, 1 oz cheddar cheese, 1 medium tomato, ½ avocado, and 2 Bibb lettuce leaves
• Snacks Creamy Lemon Smoothie; ½ cup chopped green bell pepper with 1 oz feta cheese and 2 tbsp green goddess dressing
• Dinner 6 oz whitefish with ¼ cup lentils, 1 cup green beans, and 1 tbsp butter

Day 5

• Breakfast Atkins Frozen Farmhouse-Style Sausage Scramble
• Lunch 6 oz turkey cutlets, 2 cups mixed greens, ½ cup sliced green bell pepper, ½ cup sliced cucumber, ½ avocado, and 2 tbsp raspberry vinaigrette
• Snacks ½ small apple and 2 oz cheddar cheese; 2 celery stalks with 2 tbsp feta-ranch dressing
• Dinner Pork Chops With Fresh Mushrooms, Tomatoes, and Bell Pepper with ½ small baked potato, 2 tbsp butter, and 2 tbsp sour cream

Day 6

• Breakfast Breakfast Mexi Peppers
• Lunch Cucumber, Onion, and Tomato Salad With Creamy Feta Dressing and 4 oz turkey salami
• Snacks ½ avocado and 2 tbsp Greek vinaigrette; ½ medium pear and 1 oz Brie cheese
• Dinner 6 oz chicken, ¾ cup stir-fry vegetables, 1 tbsp olive oil, 1 tbsp tamari sauce, and ¼ cup brown rice

Day 7

• Breakfast Double Chocolate Protein Pancakes
• Lunch Canned Tuna with Snap Peas, Red Bell Pepper, and Tomato and ½ whole-wheat pita
• Snacks Atkins Peanut Butter Fudge Crisp Bar; ½ medium zucchini with ¼ cup hummus
• Dinner Traditional Beef Stroganoff

Atkins 100

Here’s how a week of eating on the Atkins 100 diet might look. (10)

Day 1

• Breakfast Scrambled eggs with bacon, green bell peppers, tomato, and half a whole-wheat bagel
• Snacks Small apple with 1 oz cheddar cheese; Atkins White Chocolate Macadamia Nut Bar
• Lunch Atkins Frozen Meat Lasagna with two cups of mixed greens, ½ cup sliced cucumber, 5 cherry tomatoes,  ⅓ cup shredded carrot, and 2 tbsp Creamy Italian Dressing
• Dinner Popcorn Garlic Shrimp with 2 cups steamed broccoli and cauliflower and ½ cup brown rice

Day 2

• Breakfast Milk Chocolate Protein Muffin and a small banana
• Lunch Macaroni and Cauliflower Salad with 5 oz hamburger, 2 tbsp onions, 2 tbsp barbecue sauce, and a whole-wheat bun
• Snacks Atkins Mocha Latte Shake; ½ cup strawberries and 4 oz plain, unsweetened Greek yogurt
• Dinner 6 oz chicken breast, 2 tbsp Cajun Rub, ¼ baked acorn squash, 2 cups mixed greens, 5 cherry tomatoes, ¼ cup chickpeas, and 2 tbsp Blue Cheese Dressing

Day 3

• Breakfast Atkins Farmhouse-Style Sausage Scramble with ½ cup cubed honeydew melon
• Lunch Atkins Frozen Chicken Marsala with 2 cups mixed greens, ½ cup sliced red bell pepper, and 2 tbsp Parmesan Peppercorn Dressing
• Snacks Atkins Dark Chocolate Royale Shake; 4 tbsp black bean dip with 15 corn tortilla chips
• Dinner 6 oz flank steak, 2 tbsp Barbecue Rub, 1 medium sweet potato, 2 cups baby kale, 1 small tomato, ¼ cup shredded carrot, and 2 tbsp Maple-Dijon Dressing

Day 4

• Breakfast Atkins Frozen Ham and Cheese Omelet
• Lunch Grilled Lime Chicken Over Spinach Salad With Feta-Ranch Dressing and Sweet Cherry Pie
• Snacks Atkins Mocha Latte Shake with a small banana; 1 large tomato with 4 tbsp hummus
• Dinner Quick Barbecued Pork and Classic Coleslaw with whole-wheat bun and ¼ of a whole acorn squash

Day 5

• Breakfast French Toast Loaf with ¼ cup blueberries and 10 pecan halves
• Lunch Chicken Salad Sandwich With Grapes and Walnuts
• Snacks ½ medium cucumber and 4 tbsp black bean dip; Atkins Peanut Butter Fudge Crisp Bar and 1 small apple
• Dinner Atkins Frozen Stone Fired Three Meat Pizza With 2 cups mixed greens, ½ cup sliced green bell pepper, ⅓ cup chickpeas, 2 tbsp of Garlic Ranch Dressing, and Cinnamon-Almond Meringues

Day 6

• Breakfast Orange-Sour Cream Waffles With Fresh Blueberry Sauce
• Lunch Atkins Frozen Mexican-Style Chicken and Vegetables with ½ cup wild rice
• Snacks Atkins French Vanilla Shake; ½ whole-wheat bagel with 1 tbsp cream cheese
• Dinner Fajita Steak and Fresh Guacamole with ¼ cup black beans, ¼ cup Salsa Cruda, and two 6-inch corn tortillas

Day 7

• Breakfast Protein Powered Oatmeal and ½ cup blueberries
• Lunch Daikon and Celery Salad with 3.2 ounces Italian sausage link, 1 cup whole-wheat macaroni, and ½ cup Basic Tomato Sauce
• Snacks 1 small tomato with ½ cup cottage cheese; Atkins Dark Chocolate Almond Coconut Crunch Bar
• Dinner Atkins Frozen Orange Chicken with ¼ cup brown rice and ½ cup peas

If you’re on the Atkins 20 plan, you could choose from snacks such as: (11)

• Black olives with cheddar
• Crab dip with vegetables
• Cucumber guacamole
• Kale chips
• Smoked salmon, cucumber, and cream cheese roll-ups

If you’re on the Atkins 40 plan, you can have all of the above and snacks such as: (4)

• ¾ cup of blackberries
• Greek yogurt
• A slice of whole-grain toast with almond butter
• Hummus

Followers of the Atkins 100 plan can have any snacks, so long as the daily net carbs doesn’t exceed 100 g.

Whether you’re planning for the Atkins 20, Atkins 40, or Atkins 100 diet, here are some essential foods you’ll want to shop for:

• Proteins, including pork chops, chicken, ground beef, salmon, steak, and whitefish
• Vegetables like asparagus, broccoli, cauliflower, radishes, mushrooms, and spinach
• Fats like olive oil and butter
• Fruits like avocados
• Full-fat dairy products like cheddar cheese, blue cheese dressing, and cream

You can find more suggested meal plans and shopping lists on the Atkins website.

With a little planning, it’s entirely possible to stick to the diet while dining out. First, consider the food genre when you choose a restaurant. “Pick a restaurant that serves more protein-based dishes, such as an American restaurant over an Italian restaurant,” says Rebecca Guterman, RD, a clinical dietitian at Mount Sinai Hospital in New York City.

And scan the menu online before you arrive so you can plot your order ahead of time. Look for dishes that center on lean meats and vegetables, Rissetto says. A safe bet is a salad topped with grilled chicken or a burger with no bun and a side salad, she says.

Here are a few low-carb dishes at popular restaurants around the country: (12)

• Chili’s Chicken or Steak Fajitas without tortillas and toppings and with a double serving of vegetables instead of rice
• Olive Garden Herb-Grilled Salmon with Parmesan garlic broccoli on the side
• The Cheesecake Factory Pan Seared Branzino with Lemon Butter
• P.F. Chang’s Shrimp With Lobster Sauce

Avoid adding condiments to your meal (ketchup, honey mustard, and barbecue sauce are sneakily high in carbs), and opt for a side salad or extra vegetables over a starchy side. (12)

Like any popular diet, there are both benefits and risks to following a restricted eating plan. Here’s a look at some of them for the Atkins diet.

Pros

There are a handful of possible pros to following the Atkins nutritional approach.

For one, the diet is relatively easy to stick to. “People feel it’s easy to follow,” says Susan Kraus, RD, a clinical dietitian at Hackensack University Medical Center in New Jersey. “You focus on a few food groups, and there’s simplicity in that you don’t have to measure foods, and you’re not feeling deprived.”

And there is compelling scientific evidence that eliminating processed foods from your daily diet and replacing them with real-food choices like leafy greens and healthy fats — a foundation of the Atkins plan — can have a significant positive effect on your health and even reduce your risk of chronic diseases. In fact, a review from 2020 in the journal Nutrients concluded that the body of research over the last decade against processed foods was so strong that it pointed to the need for fundamental changes in food sourcing and manufacturing overall.

Following the low-carb fad diet may also help people with type 2 diabetes who are looking for a solution to high blood sugar. Reducing carbohydrates can deliver health benefits, regardless of whether you are trying to lose weight. For example, a 2015 review showed that carbohydrate restriction can help in the treatment of type 2 diabetes and metabolic syndrome. (13)

Cons

On the flip side, you’re not getting a well-balanced diet with the Atkins Nutritional Approach. “With any diet that eliminates a whole food group, you’re not going to get all your nutrients,” says Barbara Schmidt, RD, a nutritionist in private practice in New Canaan, Connecticut.

Then there’s the lack of fiber, an important nutrient that can help you feel full and curb unhealthy cravings. “Omitting all these food groups — [such as] grains and fruit — even if you make up nutrients with a vitamin and mineral supplement, you’re not getting enough fiber,” Kraus says. “There are also many phytochemicals, which are compounds found naturally in fruits and veggies, that provide strong antioxidant effects and might not be found in a general multivitamin and mineral supplement, along with fiber, calcium, and vitamin D, which would not be gotten by eating this way.”

Last, the Atkins diet may cause dehydration, which could lead to lightheadedness or energy loss. (14) Carbs hold on to water in your body, so when you don’t eat carbs, you lose a lot of water weight. This can also raise your uric acid level and cause a gout attack, increase calcium loss through urine, and overwork your kidneys and liver, says Kraus.

Researchers caution that although high-protein diets may be beneficial for some people looking to lose weight, it’s important to consult your healthcare provider to make sure this approach is safe for you. (15) Some research shows a high-protein diet may lead to reduced kidney function in women with prior mild renal dysfunction. (16)

Regardless, if you’re upping your protein intake, be sure to drink extra water. The Atkins diet recommends drinking at least eight 8 oz glasses of water per day. (14)

“In the short term, by following the Atkins diet, you can see results quickly. You limit food intake because you naturally don’t feel hungry,” says Kraus. “A generally healthy person can be on it for a few months without adverse effects.” Even if you don’t lose weight, your health might still benefit. A 2019 study found about half of its participants, who were people with obesity and metabolic syndrome (which can lead to type 2 diabetes) at the start of the study, no longer classified as having metabolic syndrome after following a low-carb diet for four weeks. (17)

It may not be good to eat this way forever, though. Following a low-carb diet may increase the risk of atrial fibrillation (afib), which is a common heart rhythm disorder. (18) Kraus also has concerns that it can affect the way dieters view food: “Drastic plans cause a warped view of how to lose weight, creating a different sense of what’s okay and what’s not okay. A dieter might be mortified to have a little pasta or slice of bread.”

As low-carb diets have grown in popularity, researchers have conducted a number of studies to assess the diets' effectiveness and additional health effects. The Harvard School of Public Health notes that some research shows low-carb diets can help people lose weight more quickly — and maintain it better —  than low-fat diets can, and that moderately low-carb diets can be heart-healthy. (19)

A meta-analysis from 2012 looked at 23 randomized controlled trials with more than 2,500 participants. (20) The researchers found that, compared with participants on a low-fat diet, participants on a low-carb diet experienced a small but statistically significant reduction in total cholesterol and triglyceride levels, and at least similar reductions in weight, waist circumference, and other disease risk factors. Another study, published in 2018, found low-carb dieters were able to maintain weight loss because they burned about 200 extra calories per day compared with those following a diet with higher carbs. (21)

The low-carb diet works like this: When carb intake is low, the body is forced to burn fat for fuel instead, creating ketone bodies that are used for energy, Popeck explains. Ketones are by-products of metabolism, and they are produced during a process called ketosis, when the body turns to burning fat rather than carbs — a common phenomenon in those people who follow low-carb diets, such as the Atkins diet and the keto diet.

But Popeck also notes that it is unclear whether such diets work in the long run. “I believe low-carb diets may be nutritionally unbalanced and difficult to maintain,” she says. “I work with many patients in my clinic who have tried the Atkins diet and successfully lost weight, but then [they] regain the lost weight and in turn have a difficult time losing weight again.”

That’s why she doesn’t recommend them. “I don’t like to promote diets, because most people view them as temporary,” she explains. “For some, a low-carb program may pave the way toward healthier choices simply by eliminating sugars, sweets, and processed foods. Overall, though, in my experience, feelings of deprivation usually lead to rebound bingeing, not permanent change.”

Instead, she says, she encourages her clients to try to think of diet planning more as a lifestyle — one in which all foods can fit.

Additional reporting by Julie Davis Canter and Stephanie Bucklin.