In a field of fad diets that quickly fizzle, the Atkins plan stands out from the crowd. For almost five decades, it’s been a go-to weight-loss approach based on a simple philosophy: Eat fewer carbs—well, way fewer carbs. At the most recent height of its popularity, in the early 2000s, it probably seemed like everyone you knew was giving Atkins a shot, ordering cheeseburgers without the buns and piling breakfast plates high with eggs and bacon. And that bread-banishing lifestyle still attracts plenty of fans: Research shows the percentage of adults on a low-carbohydrate diet like Atkins more than doubled from 2007 to 2017.
“Atkins is appealing to people because of its clear-cut guidelines,” says Julie Stefanski, RDN, a registered dietician nutritionist and a spokesperson for the Academy of Nutrition and Dietetics. There’s no guesswork or wiggle room—you simply have to choose from a limited list of foods (mostly protein and fat with a small amount of carbohydrates from certain fruits and veggies).
In exchange for following the diet exactly as it’s written—no sneaking in forkfuls of fettuccini when nobody is looking—Atkins promises speedy weight loss, better appetite control, and more. But does it really work? Keep reading to see if sending grains down the drain is a smart idea.
What is the Atkins diet?
The Atkins diet is a weight-loss plan that involves eating almost no carbohydrates, a moderate amount of protein, and a high amount of fat. It was developed by cardiologist Robert C. Atkins, MD, who first outlined the approach in his 1972 book, Dr. Atkins’ Diet Revolution. Dr. Atkins believed that a practically carbless diet was the key to weight loss, blood sugar control, and heart health—a controversial notion in an era when fat—not bread or pasta—was seen as public-health enemy No. 1. His reasoning: Eating very few carbs causes your body to enter ketosis, which is when it doesn’t have carbohydrates to burn for energy, so it burns fat instead.
The original Atkins diet limited the daily carbohydrate intake to 20 grams (roughly the amount in 2 cups of steamed broccoli or 1.5 cups of cherry tomatoes), so the majority of energy came from fats and protein. Today, there’s a little more flexibility. You can choose from three plans that allow different amounts of carbs per day: 20 grams, 40 grams, and 100 grams. The other big update: You now count net carbs, which is the total carbohydrate content of a food minus its fiber and sugar alcohols (sweeteners that naturally occur in some fruits and vegetables).
Atkins diet vs. keto diet
Because the Atkins diet results in ketosis (at least in the more restrictive phases), it could be described as being a ketogenic, or “keto,” diet. But that doesn’t mean it’s the same as the ketogenic diet, which follows a slightly different approach to going low-carb.
The keto diet requires you to limit total carbohydrates to 5 to 10% of your calories and caps protein at 10 to 20% of calories (this is to prevent the body from converting protein to carbohydrates). Atkins, on the other hand, increases the carb limit over time (or, in some plans, starts out with higher allowed amounts from the get-go), uses net carbs instead of total carbs (so it doesn’t count fiber and sugar alcohol), ups protein to 20 to 30% of total calories, and includes more carbohydrate-rich foods in some of the plans.
These differences may make the newer Atkins plans a little easier to stick with and also gentler on your digestive tract. “Reintroducing nutritious choices, such as fruits and whole grains, can help prevent constipation, which is one of the most common side effects [of these types of diets],” says Elisabetta Politi, RD, a certified diabetes educator with the Duke Lifestyle and Weight Management Center.
Atkins diet plans
The Atkins diet has three different plans to choose from—Atkins 20, Atkins 40, and Atkins 100—and each is intended for a different goal. While the plans differ slightly in terms of the foods you can eat, they all rely on a similar foundation of limited carbs, primarily from non-starchy veggies, along with two to four servings of protein, and three servings of fat a day.
Atkins 20
This is pretty much the original Atkins plan and is also the most restrictive. The Atkins organization recommends this version if you want to lose 40 pounds or more, but you can also use it if you have less weight to drop by skipping the first phase.
- Phase 1: This is an ultra-low-carb phase—you’re limited to only 20 net grams a day—and you’re supposed to stay on it for at least two weeks or, if you want, until you’re within 15 pounds of your goal weight. During this phase you’ll mostly eat proteins and fats, including: beef, lamb, pork, poultry, cheese, eggs, fish and shellfish, bacon, olive and vegetable oils, and butter. For carbs, you’re limited to a short list of veggies like eggplant, spinach, mushrooms, broccoli, and bell peppers. Many nutritious foods—such as whole grains, fruit, starchy veggies, beans, and dairy—are off-limits.
- Phase 2: You stay on this phase until you only have 10 pounds left to lose. The net carb limit gradually increases to between 30 and 80 grams, allowing you to up your intake of non-starchy veggies. In addition to the permitted foods from phase one, you can eat moderate amounts of whole-milk dairy, berries, melon, nuts and seeds, and legumes.
- Phase 3: This phase is geared toward reaching your goal weight and figuring out the ideal number of carbs required for you to stay there. You’ll add 5 to 10 grams of net carbs to your daily allowance until you’re between 80 and 100 grams a day. During this phase, you can also add small portions of starchy vegetables; a wide variety of fruit; as well as whole-grain bread, pasta, rice, and cereal. Once you’ve reached your weight-loss goal and stayed there for a month, you can go to the final phase.
- Phase 4: This is more of a lifestyle than a phase, since it focuses on a long-term eating strategy for keeping the scale steady. Your carb intake could be similar to phase 3 levels or it could be higher, depending on whether or not it causes weight to creep back on. The idea is that you make adjustments as pounds come on and off.
Atkins 40
This plan and the next one are both a lot simpler to follow, since there aren’t any phases to move between. As its name implies, this plan allows 40 grams of net carbs a day from the very beginning. It’s recommended for people who have 40 pounds or less to lose, but it can also be a fit for anyone who wants to follow a low-carb diet without having to go through the complicated (and super-restrictive) steps of the Atkins 20. With Atkins 40, your carbs are divided between breakfast, lunch, dinner, and snacks. The permitted foods are similar to those in phase one of Atkins 20 (so, proteins and fats with a tiny bit of non-starchy vegetables), but you’re also allowed a few small servings of other carbohydrates such as: whole-milk dairy, nuts and seeds, fruit, starchy veggies, legumes, whole grains, and alcohol.
Atkins 100
This plan, which allows 100 grams of net carbs a day, is designed for people who are pregnant, nursing, or just trying to maintain their weight. It’s a way to eat fewer carbs than most people eat while still enjoying fruit, whole grains, nuts, and starchy veggies. For comparison, the Dietary Guidelines for Americans recommend carbs make up 45 to 65 percent of total calories, which would be 225 grams or more for someone eating a 2,000 calorie diet.
What you can and can’t eat on Atkins
Although each Atkins plan is slightly different, they’re all based on the same foundation of foods. Because the list of restricted items can seem like a lot, it’s a good idea to know exactly what is and isn’t allowed before deciding to start this diet. Here are just some of the foods that you can and can’t eat:
Atkins diet foods
Each Atkins diet centers around proteins and fats with some non-starchy vegetables sprinkled into the mix. The foods you’ll be eating the most include:
- Fish: Salmon, flounder, tuna, trout, cod, halibut
- Meat: Beef, pork, bacon, ham, pork
- Poultry: Chicken, duck, turkey
- Shellfish: Crab, oysters, shrimp, clams, mussels, lobster
- Eggs
- Fats and oils: Butter, mayonnaise, olive oil, vegetable oils
- Beverages: Clear broth, club soda, coffee, tea, cream, soy/almond milk, flavored calorie-free seltzer
- Cheese: Parmesan, goat, cheddar, mozzarella, cream cheese, Swiss cheese
- Non-starchy vegetables: Spinach, arugula, olives, mushrooms, zucchini, cauliflower, broccoli, asparagus, eggplant, kale, green beans, Brussels sprouts, tomato
Foods to avoid on Atkins
No matter which plan you’re following, you aren’t allowed to eat anything high in processed carbs and simple sugars. Off-limits items include:
- Cookies, cakes, and donuts
- Soda
- Candy
- Bagels
- White bread, rice, and pasta
- Sweetened and refined-carb cereals
Benefits of a low-carb diet: 5 common claims
Following a diet that restricts an entire category of food is tough, which is why you’re probably wondering if it’s worth it. In other words: Just what kind of results can you expect if you follow Atkins? Here’s a closer look at what cancelling carbs can—and can’t—do:
Claim 1: Atkins results in greater weight loss
Research shows that following an Atkins diet can result in weight loss—not exactly surprising since you’ll probably eat fewer calories if you’re avoiding all breads, pastas, and desserts. In one small study, researchers divided a pool of 311 women into four groups, with each person following a popular diet that ranged from low-carb to high-carb (Atkins allowed the fewest). After 12 months, the group doing the Atkins diet lost more weight—around 10 pounds total on average—than volunteers who were doing the other three. But the researchers went on to say the bigger weight loss could be partly due to the higher protein intake that happens in the Atkins plan, as opposed to just the reduced carbs.
Other studies paint a slightly different picture. One small British study compared the original Atkins diet with other weight loss programs and found that while people on Atkins lost more weight during the first four weeks, weight loss was similar for all participants by the six-month mark.
One explanation for the fast-at-first weight loss is that going low carb results in a steep drop in water weight, according to Monica Reinagel, a licensed dietician/nutritionist and host of the Nutrition Diva podcast. This is because your body likes to hold on to carbs for later energy, so it stores them in the form of glycogen. And when glycogen gets stored, it’s bound up with water. If you stop eating carbs (as you would in phase 1 of Atkins 20), the glycogen gets burned, and all of the water it was stored with gets flushed out of your body. But as soon as you stop limiting carbs, the glycogen stores get replenished and water weight returns.
It’s also just plain hard to stick with a carbless lifestyle. “Eventually people start eating more high-carb foods without reducing all of the diet’s high-fat foods,” Stefanski says. “It can be very disappointing to lose weight and then gain it all back.” In general, creating successful lifestyle changes happens when diets are sustainable.
Claim 2: Atkins can help control appetite
A restrictive diet where you aren’t ravenous the whole time? That’s something Atkins might be able to deliver. Whenever you eat, your body produces a hormone called peptide YY—it reduces your appetite and makes you feel more satisfied. Normally, losing weight causes peptide YY production to go down (causing you to still feel hungry after a meal), but the drop isn’t as big on a low-carb diet compared to a low-fat one. “Reducing your carbohydrate intake also lowers circulating levels of insulin, a hormone that’s associated with an increased appetite,” Politi says. That, plus the higher protein and fat intake with Atkins, may combine to keep you feeling full.
Claim 3: Atkins can improve blood sugar
While going on a low-carb diet may improve blood glucose levels and insulin sensitivity, this is probably due to weight lost on the diet as opposed to Atkins having some unique blood-sugar effect, research has found.
Claim 4: Atkins can lower cholesterol levels
The Atkins diet isn’t especially helpful to cholesterol levels, but on the flip side, it also doesn’t make them much worse (something you’d think might happen since it’s so high in saturated fat). Some research shows following Atkins can increase healthy HDL cholesterol levels. However, “it’s not clear if the increase is actually beneficial,” says Penny Kris-Etherton, PhD, a registered dietician and Evan Pugh University professor of nutritional sciences at Penn State University. Atkins may increase what’s known as “non-functional” HDL, which isn’t as good at clearing cholesterol from the arteries. The Atkins diet can also slightly raise levels of LDL cholesterol (the kind you want to avoid), but researchers think this doesn’t have as much of an impact on your health since it makes the LDL particles bigger, which makes them less dangerous.
Claim 5: Atkins is good for your heart
Can following the Atkins diet reduce blood pressure and other risk factors for cardiovascular disease among some people? Yes. But there’s no proof that the benefits come from the diet's low-carb quality—they may occur as a result of weight loss some people experience on the plan. There also hasn’t been research showing that these benefits translate to an actual reduced risk for heart disease.
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Possible health risks of a low-carb diet
Despite the diet's decades of existence, long-range studies on the potential health effects of the Atkins diet have not been published. That said, research does indicate the possibility of shorter-term side effects, ranging from unpleasant to potentially dangerous.
- Constipation: Don't be surprised if you experience toilet trouble while following Atkins. Without eating whole grains, it’s difficult to consume enough fiber, which makes constipation common, Reinagel says.
- Fatigue, lightheadedness, and headache: These symptoms can sometimes occur with ketosis, which happens during phase 1 of Atkins 20.
- Nutritional gaps: “Eating only small portions of fruits, vegetables, and dairy can lead to vitamin and mineral insufficiencies,” Stefanski says. Deficiencies in calcium, vitamin D, and vitamin C are especially common on low-carbohydrate diets.
- Digestive discomfort: “Fat can be difficult to digest—the process requires acid from the stomach, bile from the liver, and enzymes from the pancreas and small intestine,” Stefanski says. “If any of these systems isn’t in working order, nausea, abdominal pain, or diarrhea can occur.”
- Cardiac arrhythmia: People on a diet with fewer than 45% of calories from carbohydrates were 16% more likely to experience atrial fibrillation than those consuming 52% of calories from carbs, according to an American College of Cardiology study. The condition is a form of cardiac arrhythmia that causes a fast, irregular heartbeat which can result in poor blood flow.
- Leg cramps: The low-carb approach to eating can set off a chain reaction that could result in Charley horses and other muscle cramps. Eating lots of protein without vegetables or carbohydrates can lead to magnesium deficiency, by increasing the amount of magnesium your body releases through urine. And since magnesium is used to help your muscles function well, being low in it has been linked to muscle cramps.
The upshot: Does the Atkins diet work?
Today’s Atkins diet plans may be less restrictive than the original version, but many nutrition experts still aren’t sold on their safety or effectiveness. For one thing, the Atkins diet remains high in saturated fat, which is linked to cardiovascular disease and other diseases. What’s more, loading up on protein and fat may also come at the expense of key nutrients from fruits and veggies. Compared with other weight-loss diets, research hasn’t uncovered major health benefits unique to Atkins.
The Atkins diet does not address other key aspects of managing weight, such as physical activity and good-quality sleep, Stefanski says.
Some people do lose weight while following the Atkins diet—when they’re able to stick with it. “If a client loves protein and vegetables, Atkins may be a good choice for them. But if they love carbohydrates, I would try a different approach,” Politi says.
Newer versions of the Atkins diet allow more carbohydrates than the original plan. Still, a more balanced approach may be to take some of the good parts of the Atkins diet—eating more protein and vegetables—add in healthy whole grains, and choose heart-healthy fats to develop a way of eating you can sustain for the long haul. Whatever you decide, consult a medical professional before making any major changes to your diet, especially if you have or are at risk of a chronic health condition like type 2 diabetes.
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Karen Ansel, MS, RDN, is a journalist and author specializing in nutrition, health, and wellness. Her latest book is Healing Superfoods for Anti-Aging: Stay Younger, Live Longer.
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This article was reviewed for accuracy in September 2021 by Angela Goscilo, MS, RD, CDN, manager of nutrition at WeightWatchers®. The WW Science Team is a dedicated group of experts who ensure all our solutions are rooted in the best possible rese