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Ketogenic Diet: The Definitive Guide to Keto

Written by Emily Hirsch, MS, RD

Reviewed by Ana Reisdorf, MS, RD 

Last Updated on December 1, 2021

The keto diet is a wildly popular low-carb, high-fat diet that may be effective for short-term weight loss. In this guide, our dietitian discusses everything you need to know about the keto diet.

Ketogenic Diet: The Definitive Guide to Keto
Photo credit: iStock.com/grandriver

What Is the Ketogenic Diet?

The ketogenic diet, also known as the keto diet, is a high-fat, moderate-protein, low-carbohydrate eating pattern that has long been used to reduce seizure frequency, particularly in people with epilepsy.

More recently, the keto diet has increased in popularity as a way to lose weight.

There appear to be some other health benefits to this eating pattern, including improved blood sugar control, reduced risk factors for cardiovascular disease, and enhanced brain functioning.

Unlike other low-carbohydrate diets like the Atkins diet, which typically focuses on protein intake, the keto diet emphasizes fat intake.

By reducing your carbohydrate intake and replacing it with fat, your body will begin to burn fat for fuel, and this forces your body into a metabolic state called ketosis.

Summary

The ketogenic diet is a high-fat, moderate-protein, low-carbohydrate eating pattern to help people lose weight, and it may also have other health benefits.

What Is Ketosis?

Ketosis is a metabolic state that occurs when the body does not have enough carbohydrates to use for energy.

When your carbohydrate stores are depleted, your body will rely on ketones, a source of energy that your liver produces from stored fat.

These ketones will become the primary energy source for your brain and other organs.

Getting your liver to make ketones involves limiting your carbohydrate intake to roughly 20 to 50 grams per day. To put this into context, one apple has between 15–30 grams of carbohydrates, depending on the size.

It is also important to note that protein can be converted into fuel for your body. Therefore, overeating protein can prevent ketosis.

This is why the keto diet suggests a moderate protein intake, which would be 10% to 20% protein from your total daily calories.

So, what foods can you eat on the keto diet? You’ll want to fill up on higher fat foods like meat, fatty fish, nuts, seeds, cheeses, and healthy oils.

Summary

Ketosis is a metabolic state in which your body uses fat for fuel instead of carbohydrates.

Types of Ketogenic Diets

There are different types of ketogenic diets, some of which are more popular for athletes.

  • Standard Ketogenic Diet (SKD): A low-carbohydrate, moderate-protein, high-fat diet. It typically contains 70% to 80% fat, 10% to 20% protein, and only 5% to 10% carbohydrates.
  • High Protein Ketogenic Diet (HPKD): This diet is similar to a standard ketogenic diet but includes more protein. It typically contains 60% fat, 35% protein, and 5% carbohydrates.
  • Cyclical Ketogenic Diet (CKD): This eating pattern involves periods of higher carbohydrate intake, for example, five ketogenic days followed by two high-carbohydrate days, and is generally used for bodybuilders or athletes.
  • Targeted Ketogenic Diet (TKD): This diet is similar to a standard ketogenic diet but allows you to add carbohydrates around your workout schedule. TKD is also used for bodybuilders and athletes.

Summary

The standard ketogenic diet is most commonly used, but there are different types of keto diets, some of which are geared towards athletes.

Health Benefits

This high-fat, moderate-protein, low-carbohydrate eating pattern can help people lose weight, in addition to other health benefits.

Weight Loss

A ketogenic diet may help you lose more weight than some other traditional diets, like a low-fat diet.

Researchers theorize that this weight loss is because you burn more calories converting fat into energy versus converting carbohydrates into energy.

In a 2020 meta-analysis of 38 studies lasting 6–12 months and including 6,499 participants, researchers found that low-carbohydrate diets led to more weight loss than low-fat diets.

One 2014 study analyzed the effects of a low-carbohydrate diet versus a low-fat diet on weight loss and cardiovascular risk factors over one year.

The study found that the low-carbohydrate diet group lost an average of 7 pounds more than the low-fat group.

Additionally, the low-carbohydrate group had more significant improvements in their HDL (good) cholesterol levels, triglycerides (TG), and greater declines in other cardiovascular disease risk factors.

One 2020 study of 34 older adults with obesity found that those who followed a ketogenic diet lost almost five times as much total body fat as those who followed a low-fat diet.

It is important to note that the study lasted eight weeks; therefore, the long-term weight loss effects of the ketogenic diet are unknown.

Summary 

The ketogenic diet may help you lose more weight than low-fat diets and improve cardiovascular health.

May Help Manage Blood Sugar for People With Type 2 Diabetes

By drastically reducing carbohydrate intake and helping the body lose fat, the ketogenic diet may help improve blood sugar control, particularly for people with type 2 diabetes.

One recent meta-analysis of clinical trials suggested that following a ketogenic diet helped diabetic patients improve their blood sugar control, increase their HDL (good) cholesterol levels, and even lose weight.

One recent 2-year clinical trial found that people with type 2 diabetes who followed a keto diet lost an average of roughly 26 pounds and experienced improved blood sugar control.

Some study participants were even able to decrease their intake of diabetes medications throughout the trial.

Summary 

Following a ketogenic diet may help people with type 2 diabetes lose weight and improve their blood sugar control.

May Help Prevent Cardiovascular Disease

Following a keto diet may help decrease risk factors for cardiovascular disease.

According to one 2017 study, the ketogenic diet may be associated with some improvements in cardiovascular health by reducing “bad” cholesterol levels and increasing “good” cholesterol levels.

However, researchers noted that there need to be more long-term studies done to analyze this connection further.

Summary 

Following a ketogenic diet may improve your heart health; however, more research is needed to establish a clear link.

Can Help Minimize Seizure Disorders

The ketogenic diet was initially developed to treat epilepsy in children nearly 100 years ago. The ketogenic diet remains an effective treatment for some children and adults to help to control seizures.

Scientists are unsure how the keto diet may be an effective intervention in seizure disorders, but they theorize that the production of ketones, the increase in fatty acids, and the reduced blood sugar all play a role in minimizing seizures.

One 2018 study suggests that one-third to one-half of people with drug-resistant epilepsy can reduce seizure frequency by at least 50% with a ketogenic diet.

Summary

The ketogenic diet may be an effective treatment option for seizure disorders.

May Benefit Brain Health

Some studies suggest that following a ketogenic diet may protect the brain from Parkinson’s and Alzheimer’s diseases and help to reduce symptoms in patients with these diseases.

One 2019 review suggests that the diet improves cognitive performance in elderly adults with Alzheimer’s disease.

Another 2021 review found that following a ketogenic diet for people with Parkinson’s disease showed improved executive and processing speed, pain, tremors, and rigidity.

Summary

Emerging research suggests that the ketogenic diet may reduce common symptoms of both Parkinson’s and Alzheimer’s diseases.

Drawbacks

The keto diet has been shown to benefit some aspects of health; however, it is important to note some drawbacks to this highly restrictive eating pattern.

Nutrient Deficiencies

The keto diet restricts your intake of most fruits, some vegetables, and most grains.

This restriction can place you at an increased risk of nutritional deficiencies, including magnesium, potassium, phosphorus, selenium, and vitamins C, B, D, and E.

It is best to speak with your healthcare provider to see if taking a multivitamin while following the keto diet may be safe and of benefit for you.

Summary

Due to its highly restrictive nature, the keto diet may lead to nutritional deficiencies.

Keto Flu

The keto flu is a cluster of symptoms that can appear anywhere from 2 to 7 days after beginning the keto diet.

The symptoms result from your body adjusting to ketosis and generally pass within a week or so.

Common keto flu symptoms include:

  • Headache
  • Fatigue
  • Dizziness
  • Irritability
  • Gastrointestinal distress, including nausea, vomiting, and diarrhea
  • Poor concentration
  • Decreased energy
  • Feeling faint
  • Difficulty sleeping

Summary

During the first week of the keto diet, you may experience flu-like symptoms while your body is adjusting to being in a state of ketosis.

May Increase Cholesterol Levels

The high fat intake of the keto diet may drive up your cholesterol levels.

One 2018 study of young adults found that after 12 weeks on a ketogenic diet, participants experienced a 35% increase in their LDL (bad) cholesterol levels.

Summary

Due to its high fat intake, following the keto diet may increase cholesterol levels.

Can Lead to Constipation

A keto diet is low in fibrous foods like fruits, whole grains, and legumes. Reducing your intake of high-fiber foods can increase your risk for constipation.

Summary

The keto diet is low in fiber, which may lead to constipation.

Difficult to Sustain

Due to its restrictive nature, following the keto diet is very difficult to sustain long term.

Many people begin the keto diet, lose weight, and then once they stop the diet, generally gain all of the weight back plus some extra.

Summary

Due to its restrictive nature, the keto diet is difficult to sustain long term.

May Be Harmful to Certain People

According to the Academy of Nutrition and Dietetics, the keto diet may be harmful to specific groups with specific health conditions.

For example, the eating pattern is not recommended for people with:

  • Pancreatic disease
  • Liver disease
  • Insulin-dependent diabetes
  • Thyroid conditions
  • Eating disorders or a history of eating disorders
  • Gallbladder disease or those who have had their gallbladders removed
  • Kidney disease

The keto diet is also not recommended for pregnant or breastfeeding women due to the potential for causing nutrient deficiencies during this vital time.

Summary

The keto diet may be dangerous for certain populations with specific health conditions.

What to Eat

Keto-friendly foods are generally low-carb and high in fat, and restricted foods are highly processed foods, unhealthy fats, all starchy foods, and most fruits.

Foods to Eat

The following are foods you can enjoy when following a keto diet:

  • Meats: Steak, ham, sausage, bacon, pork chops, chicken, turkey, lamb, and organ meats
  • Plant-based proteins: Tempeh, firm tofu
  • Fatty fish and seafood: Salmon, trout, tuna, mackerel, shrimp, crab, lobster
  • Dairy: Eggs, cheese, butter, cream, plain Greek yogurt, whole-milk cottage cheese
  • Nuts and seeds: Almonds, walnuts, flaxseeds, pecans, macadamia nuts, pumpkin seeds, chia seeds
  • Healthy oils and fats: Extra virgin olive oil, coconut oil, avocado oil, butter, ghee
  • Low-carb vegetables: Lettuce, tomatoes, onions, peppers, broccoli, cauliflower, green beans, zucchini, Brussel sprouts, asparagus, eggplant, mushrooms, spinach, and avocado
  • Lower-carb fruits: Berries, including blackberries, raspberries, strawberries
  • Beverages: Water, plain coffee, tea, bone broth, and plant-based milk, including almond milk, coconut milk, and flaxseed milk

Foods to Avoid

The following are foods that need to be limited or eliminated when following a ketogenic diet:

  • Foods high in sugar: Soda, sports drinks, candy, fruit juice, smoothies, cake, ice cream, sweetened yogurts, pastries
  • Grains and starches: Bread, tortillas, rice, pasta, cereal, chips, bagels, oatmeal, crackers, French fries, pretzels
  • All fruit: Except small portions of berries like strawberries, blackberries, and raspberries
  • Beans and legumes: All beans, including kidney beans, chickpeas, baked beans, pinto beans, lima beans, peas, and lentils
  • High-carbohydrate vegetables: Potatoes, sweet potatoes, carrots, parsnips, corn, and pumpkin
  • Some condiments or sauces: Barbecue sauce, honey mustard, teriyaki sauce, ketchup, low-fat salad dressings, low-fat mayonnaise
  • Most calorie-containing beverages: Alcohol, including beer, wine, and liquor, mixed drinks, juice, and milk

Supplements for the Keto Diet

Due to its restrictive nature, following the keto diet may lead to nutritional deficiencies and unpleasant side effects.

Taking supplements can ease some of these side effects, fill in nutritional gaps, and may increase the diet’s effectiveness.

The following are supplements to consider if you are on a keto diet:

MCT Oil (Medium Chain Triglyceride Oil)

MCT oil can be rapidly metabolized by your liver and enter your bloodstream to serve as a source of fuel for your muscles and brain.

Keto dieters may benefit from taking MCT oil as it can further promote weight loss by helping you feel fuller for longer.

MCT oil can easily be added to various foods and drinks or can be taken alone. A standard dose of MCT oil is one teaspoon.

Most people should start with this dosage as more may cause stomach upset and diarrhea. 

Summary

MCT oil can benefit those following a keto diet as it can provide fuel for your muscles and brain and help you feel fuller for longer. 

Fiber

The keto diet tends to be low in fiber, and a lack of fiber in your diet may lead to constipation.

If you’re following a keto diet and falling short of the recommended 25–31 grams of fiber per day, you may benefit from a fiber supplement.

Look for fiber supplements with no sugar, and make sure to drink plenty of water to help promote healthy digestion. 

Summary

Because keto diets tend to be low in fiber, taking a fiber supplement can help prevent constipation.

Magnesium

Magnesium-rich foods tend to be higher in carbohydrates. Therefore, if you’re following the keto diet, you may be lacking in this vital mineral.

Because magnesium supplements can cause diarrhea, it’s best to initially take the lowest dose on the package.

Starting with 100 mg to 200 mg per day and then gradually increasing your dosage to 400 mg per day will help to prevent gastrointestinal upset.

If you’re looking to steer clear from magnesium supplementation, there are some keto-friendly foods that are magnesium-rich and also low in carbohydrates.

These foods include spinach, pumpkin seeds, almonds, cashews, avocado, swiss chard, and mackerel.

Summary

Magnesium-rich foods are generally high in carbohydrates; therefore, people following a keto diet may lack this nutrient. Taking a magnesium supplement or focusing on keto-friendly magnesium-rich foods can help prevent a magnesium deficiency when following a keto diet. 

Omega-3 Fatty Acids

Due to the high-fat nature of the keto diet, people following this type of eating plan may have an imbalance of omega-3 and omega-6 fatty acids in their diet. This imbalance may lead to inflammation and chronic diseases.

Taking an omega-3 fatty acid supplement can help maintain an ideal balance of omega-3 and omega-6 fatty acids in the body, which has been shown to reduce inflammation and decrease cardiovascular risk factors.

Summary

People following a keto diet may not have an ideal balance of fatty acids. Taking an omega-3 fatty acid supplement can help maintain an ideal balance of omega-3 and omega-6 fatty acids in the body, help reduce inflammation, and decrease cardiovascular risk factors.

Sample Meal Plan

Below is a 1-week sample ketogenic diet meal plan.

Monday

  • Breakfast: Omelet with diced tomato and cheddar cheese
  • Lunch: Bacon lettuce wraps with tomato and avocado
  • Dinner: Steak with sautéed spinach in olive oil

Tuesday

  • Breakfast: Whole milk, plain Greek yogurt with chia seeds and strawberries
  • Lunch: Cobb salad with egg and bacon
  • Dinner: Stuffed peppers with a side salad

Wednesday

  • Breakfast: Egg casserole with spinach, feta, and tomato
  • Lunch: Turkey cheddar roll-ups with an avocado salad
  • Dinner: Stuffed chicken breasts with a side of asparagus sautéed in butter

Thursday

  • Breakfast: Crustless quiche with veggies and mozzarella cheese
  • Lunch: Keto-friendly chili topped with shredded cheese and sour cream
  • Dinner: Salmon with a fresh spinach salad

Friday

  • Breakfast: Breakfast sausage with onions and peppers
  • Lunch: Cauliflower mac and cheese
  • Dinner: Zucchini pizza bites with a side salad

Saturday

  • Breakfast: Omelet with chorizo and spinach
  • Lunch: Taco shrimp lettuce wraps
  • Dinner: Creamy chicken with cauliflower mash

Sunday

  • Breakfast: Keto pancakes (made with almond flour and coconut flour) topped with butter
  • Lunch: Salmon salad with spinach and avocado
  • Dinner: Zucchini lasagna

Keto Snack Ideas

Looking for something to munch on in between meals? The following are some keto-friendly snacks to help curb your appetite:

  • Veggie sticks with guacamole
  • A handful of nuts or seeds
  • Olives
  • Full-fat Greek yogurt or coconut yogurt
  • Cheese
  • Hard-boiled eggs
  • Cottage cheese
  • Beef jerky
  • Seaweed snacks

Tips on Starting the Keto Diet

If you’ve decided to begin the keto diet, one of the best tips for initial success is to keep things simple.

For example, plan your meals by selecting a protein, a low carbohydrate veggie, and a fat.

Your protein choices may include beef, salmon, chicken, pork, or eggs.

Your low-carb vegetable choice could be a greens salad, cauliflower, broccoli, asparagus, zucchini, brussels sprouts, cucumbers, or bell peppers.

For fat, you may choose butter, oil, cheese, ghee, or avocados.

When starting the keto diet, you’ll want to have your refrigerator fully stocked with keto-friendly foods like:

  • Low carbohydrate vegetables: lettuce, zucchini, asparagus
  • Healthy fats: butter, coconut oil, avocado oil
  • Proteins: beef, pork, chicken, turkey, eggs, fish, and shellfish
  • Full-fat dairy: cheese and heavy cream

Additionally, you’ll want to stock your pantry with the following keto-friendly foods:

  • Plenty of herbs and spices
  • Low carb condiments: hot sauce and mustard
  • Nuts and seeds: almonds, cashews, pumpkin seeds, and sunflower seeds
  • Low carbohydrate flours: almond flour, coconut flour, and flaxseed meal

When beginning a keto diet, it is best to start slowly. Rather than eliminate all carbohydrates right away, cut back on foods gradually.

For example, eliminate all sugary foods first, like cookies and candy, then complex carbs like bread and pasta, and then starchy veggies and fruit last.

Tips on Dining Out

If you’re following the keto diet but still want to eat out, the following are some tips to help you stay on track at restaurants:

  • Focus your meals on meat or fish and replace higher-carbohydrate foods with extra vegetables. 

  • If you’re in the mood for a sandwich or a burger, ask the waitstaff to substitute lettuce wraps for the bun.

  • When ordering a salad, be sure to include a protein like salmon, and opt for oil and vinegar rather than sugar-laden salad dressings.

  • Steer clear from sugary sauces and condiments like ketchup, cocktail sauce, BBQ sauce, and honey mustard. Alternative condiments like mustard, salsa, or guacamole are keto-friendly and can add plenty of flavor to your favorite dishes. 

  • For beverage selections, water, sparkling water, tea, or coffee are all keto-friendly. If you want an alcoholic beverage, some low carbohydrate choices may include dry wine, champagne, or light beer. 

Frequently Asked Questions About the Keto Diet

  • Is the keto diet healthy?

    While it may help with short-term weight loss and improve blood sugar control, the keto diet is highly restrictive and may lead to unpleasant short-term side effects like the keto flu.

    Additionally, since the diet eliminates most fruit and dairy, whole grains, many vegetables, and legumes, you may be more susceptible to nutrient deficiencies and constipation if you remain on the diet long term.

  • What are the rules of the keto diet?

    A healthy ketogenic diet should consist of about 75% fat, 10–30% protein, and no more than 5% or 20 to 50 grams of carbs per day.

    When following the keto diet, you’ll want to focus your intake on high-fat, low-carb foods like eggs, meats, dairy, and low-carb vegetables.

    Be sure to restrict highly processed foods, unhealthy fats, all starchy foods, and most fruits.

  • What foods can I eat on the keto diet?

    In following the keto diet, you’ll essentially be replacing high carbohydrate foods with foods higher in fat and protein.

    Your focus should be on meats, fatty fish, cheese, nuts, seeds, eggs, full-fat dairy, low-carbohydrate vegetables, and healthy fats.

  • Is the keto diet easy to follow?

    The keto diet can be challenging to follow because it is highly restrictive. Many people will begin the keto diet, lose some initial water weight, and then go back to eating carbohydrates. People that do not stick with the diet tend to gain their weight right back.

    Additionally, the keto diet is very high in fat and protein and lacks fruits and vegetables, which may pose some health issues for certain groups of people.  

  • Is the keto diet safe?

    The keto diet is generally safe for short-term use; however, there is minimal research on whether the diet is safe for long-term use.

    It is important to note that the keto diet is not safe for the following groups:

    • People with pancreatic disease, liver, gallbladder, or kidney disease

    • People with insulin-dependent diabetes

    • Women who are pregnant or breastfeeding

    • People with thyroid conditions

    • People with eating disorders or a history of eating disorders

  • How do I know when my body is in ketosis?

    Signs and symptoms of ketosis may include increased thirst and urination, dry mouth, “keto breath” characterized by a bad or fruity scent, digestive issues including constipation or diarrhea, and decreased appetite.

    You can also use a urine test strip to test for ketones. They are easy to use and can be purchased at your local pharmacy or online.

  • How much weight can I lose on the keto diet?

    During the first week on the keto diet, you will likely lose somewhere between 2 and 4 pounds. However, it’s important to note that much of that initial weight loss is water.

    After 2 to 3 weeks, you may begin to see a steady weight loss of about 1 pound per week. This weight loss will vary depending on your food intake and activity levels.

  • How long can you stay on the keto diet safely?

    Due to its restrictive nature, you should not follow the keto diet for longer than six months. After following this diet, it is best to introduce carbohydrates back into your diet slowly.

    For example, you may want to add 15–30 grams of carbohydrates per day as you begin to wean yourself off of the keto diet. It's also important to continue exercising and drinking plenty of water. 

The Bottom Line

The keto diet is a high-fat, moderate-protein, low-carbohydrate eating pattern that has been used to promote weight loss in recent years.

The research surrounding the keto diet for reducing seizures in people with epilepsy is compelling.

Additionally, the ketogenic diet may help you lose more weight than some other traditional diets, like a low-fat diet.

Other health benefits to this eating pattern may include improved blood sugar control, reduced risk factors for cardiovascular disease, and enhanced brain functioning.

However, the keto diet has some significant drawbacks due to its restrictive nature. For example, it may lead to nutritional deficiencies, constipation, and the “keto flu.”

Moreover, the research surrounding the long-term use of the keto diet for weight management is lacking.

Whether this restrictive diet over an extended period is more beneficial than a healthy, well-rounded, balanced diet remains unclear.

If you’re tempted to jump on the keto bandwagon, it’s best to speak with your healthcare provider to ensure that it’s a safe eating pattern for you.

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