The Ketogenic Diet: A Guide for Beginners

The ketogenic, or keto, diet very low-carb, high-fat diet that aims to put your body into a state of ketosis. Some keto dieters lose an impressive amount of weight very quickly. But how safe is this diet?
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Key Takeaways of the Keto Diet

  • Do: Eat high-fat, high protein foods, such as avocado, seafood, eggs and full-fat dairy.
  • Don't: Eat whole-grains and other high-carb foods, such as sweets, pasta and bread.
  • Benefits: For short-term weight loss, this diet does the job.
  • Risks: Experts caution following this diet long term because of possible health risks, including nutritional deficiencies. It could be unsafe for some people.

What Is the Keto Diet?

The ketogenic – or "keto" – diet is a high-fat, low-carb diet that aims to burn fat to help people lose weight. The goal of the diet is to quickly lose weight without hunger or cravings. Proponents of the diet say it can boost mood, improve mental focus and increase energy.

Because this is a low-carb diet, foods on this diet are high in protein and healthy fats.

What Is Ketosis?

When you deprive the body of carbohydrates and force it to rely almost exclusively on fat, you trick it into believing it is starving. Starvation causes the formation of ketones, substances produced in the liver to be used for energy in the absence of food. Ketones in the urine indicate that the body is acidic – a good sign for people trying to lose weight on this diet, but an indicator of a health emergency for someone with diabetes not on the keto diet.

Ketosis usually happens after two to four days of eating fewer than 20 to 50 grams of carbohydrates a day, though each person is different. Some people may need to restrict more carbs to fully enter ketosis.

While similar in some ways to other low-carb diets, the keto diet is more restrictive, with no more than 20 net carbs daily. A net carb is the carbohydrate that your body digests. It's calculated by taking the total carbohydrates in a food and subtracting the sugar alcohols (used in sugar-free foods) and fiber. For example, one slice of bread can easily contain 20 net carbs.

Is It Easy to Follow?

Experts say the keto diet is a restrictive eating regimen and is difficult to follow in the long run. To follow it, one must be educated on which foods contain carbs and have the skills and desire to prepare appetizing high-fat meals over the long term.

A keto diet is a major change in most people’s eating habits. It’s also an unpleasant change, as many of our favorite foods, including bread, pasta, cereal, sweet fruits and starchy vegetables, are forbidden.

“To truly be in ketosis, you must consume 80% of your calories from fat, which, over time, can become boring, unappetizing and unsustainable,” says Lexi Endicott, a registered dietitian and culinary nutrition specialist with To Taste, a culinary nutrition consulting and education company.

How Does the Keto Diet Work?

Carbohydrates are the body's preferred source of energy. When carbs are consumed, the liver converts them into glucose to fuel the body. However, on the keto diet, you’ll be eating far fewer carbohydrates than you’re likely used to enjoying.

When there isn’t enough glucose, your body starts breaking down stored fat for energy instead, which can cause you to lose weight.

As part of the keto eating regimen, the macronutrients are broken down into the following:
  • Fat: 70% to 80%
  • Protein: 10% to 20%
  • Carbohydrates: 5% to 10%
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Can the Keto Diet Help Me Lose Weight?

Research suggests that the keto diet can be effective for short-term weight loss, but in the long run, it may not be any better than low-fat diets that allow for more carbs.

“It is not clear if the keto diet works or is safe in the long term as a weight loss diet," says Lana Nasrallah, manager of clinical nutrition at UNC Health, a not-for-profit integrated health care system based in Chapel Hill, North Carolina.
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Health Benefits of the Keto Diet

For some people, the keto diet has been associated with certain health benefits, including:
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Health Risks of the Keto Diet

Due to the highly restrictive nature of the keto diet, experts do not recommend it long term. Such an approach may lead to vitamin and nutrient deficiencies.

“Any diet that discourages certain food groups, such as carbs, is not good for long-term weight loss,” says Lisa D. Ellis, a registered dietitian in private practice in Manhattan and White Plains, New York.

The first symptoms of keto’s adverse effects are so well known they even have a name: the keto flu. Keto flu symptoms include:
There are some concerns that following a keto diet may have other adverse effects, according to a recent review of studies. In addition, according to the Academy of Nutrition and Dietetics, the high-fat, high-protein content of the keto diet is “very controversial.” A vast amount of research has linked diets high in saturated fat with an increased risk for heart disease, diabetes, cancer and many other chronic health problems.
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What Foods Can I Eat on the Keto Diet?

Here's a list of healthy foods to eat on the keto diet:

Dietary Restrictions

Diet modifications are possible when following a keto diet:

  • Vegan. In a keto diet for vegans, you’ll need to rely on high-fat, plant-based foods, including coconut oil and nuts, for most of your calories. Choose coconut milk and cream, vegan cheese alternatives and ground flaxseed to replace dairy products and eggs. See all vegan diets.
  • Vegetarian. Vegetarians can select tempeh, tofu and seitan as protein sources while on the keto diet. Avocado, coconut and olive oils are healthy plant-based fats. See all vegetarian diets.
  • Gluten Free. When you eliminate carbs on the keto diet, you also rid your menu of most gluten-containing foods. See all gluten-free diets.
  • Halal. You’ll be able to find halal-compliant meat and poultry at a halal butcher or some national supermarket chains. See all halal diets.
  • Kosher. Because the keto diet is generally rich in butter, you’ll need to find suitable replacements, such as coconut oil, for dishes containing meat to avoid mixing meat and milk. See all kosher diets.

Shopping List

You’ll want to stock your pantry with these keto-friendly foods:
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What Foods Do I Avoid on the Keto Diet?

  • Alcohol
  • Corn
  • Sweets and sugar
  • Legumes, beans, peas and lentils. They contain too many carbs to conform to the keto diet's strict limit on carbohydrates.
  • Grains, including rice, pasta and oatmeal. There are too many carbs in grains to be keto.
  • Low-fat dairy products. The fat content of full-fat dairy makes it useful for keto dieters, but low-fat or skim products don't contain enough fat to balance out the milk sugars they contain.
  • Added sugars and sweeteners
  • Sugary drinks
  • Starchy vegetables, such as potatoes, corn and peas

Keto Diet Tips and Advice

Amy Levy, a Los Angeles resident, first went on the keto diet to lose weight for her daughter’s bat mitzvah in April 2020 and quickly lost 24 pounds.

“The pandemic kind of threw me for a loop, and my dedication to the diet faded,” Levy, 54, says.

She resumed the keto regimen after watching a documentary, “The Magic Pill,” featuring interviews with people who tried the keto diet and experienced improvements in symptoms from epilepsy, cancer and other ailments. Levy hoped the diet might help fight inflammation, which would alleviate symptoms of her ulcerative colitis and arthritis. She’d already been considering eliminating refined sugar and processed foods from her diet again when she saw the documentary. Levy read up on the keto diet and spoke to her doctor, who said many patients had experienced success with the low-carb diet.

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This article is based on reporting that features expert sources.

Sources

The U.S. News Health team delivers accurate information about health, nutrition and fitness, as well as in-depth medical condition guides. All of our stories rely on multiple, independent sources and experts in the field, such as medical doctors and licensed nutritionists. To learn more about how we keep our content accurate and trustworthy, read our editorial guidelines.

Lolita Carrico, CNS

Carrico is a certified nutritionist based in Los Angeles. She's CEO of Ketology, a website with keto-friendly meal ideas, information about cookbooks and keto hacks. Carrico has also written several keto cookbooks.

Lisa D. Ellis, MS, RDN, CDN, LCSW, CEDS-C

Ellis is a nutrition therapist and registered dietitian with Integrating Nutrition, Inc. She is also an author.

Lana Nasrallah, RD, LDN, MPH

Nasrallah is a clinical dietitian with UNC Health, a not-for-profit integrated health care system based in Chapel Hill, North Carolina.

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