The Keto Diet: Everything You Need To Know Before you Begin

Ketogenic Diet

It’s difficult to cruise the internet, pick up a magazine, or watch TV without seeing or hearing something about the . It’s all the rage, and that enthusiasm ranges from many high-fives to serious warnings about the complications and side effects associated with following this eating plan.

If you have been thinking about trying the keto way of eating, it’s best to explore the pros and cons of this approach before you begin. Define what you want to achieve, what dietary changes you are willing to make and for how long, how the diet may or may not fit into your lifestyle, and what healthy alternatives to the keto diet will fulfill your needs.

What is the keto diet

The keto diet is a low-carb, high-fat, restrictive way of eating that focuses on . In fact, it is primarily touted as a fast way to drop pounds, but many experts and even proponents of the diet note that it’s not a sustainable way of eating because of its strict guidelines.

Several variations of the keto diet exist, but the two most commonly used approaches are the standard and the high-protein . In the standard approach, the breakdown of food intake is 75 percent fat, 20 percent protein, and 5 percent carbohydrates. For those who may want or need a higher protein intake, the high-protein approach is 60 percent fat, 25 percent protein, and 5 percent carbs.

The word “keto” refers to the fact that this way of eating prompts the body to produce ketones. These are substances that the liver makes when you eat very few carbs and moderate amounts of protein. The result is the insulin levels in the body become very low. When the body doesn’t have enough insulin to convert glucose (sugar) into energy, it must find another source. That source is fat, which makes up the majority of the keto diet.

The liver transforms the fat into ketones and ships them off to the bloodstream. The body then burns ketones/fat rather than glucose for energy. The most obvious benefit is that you begin to lose weight, but there are some other benefits as well, as you shall learn.

Read about is the ketogenic diet for you?

How does it work: ketosis

Ketosis is a normal function in your body. It is a metabolic condition in which the brain switches from using glucose as its energy source and instead must use ketones. When you don’t consume enough carbohydrates from food so your cells can burn them for energy, it needs to turn to fat instead as its energy source. That’s when your body creates ketones.

If you are eating a balanced diet that roughly consists of 15 to 20 percent protein, 50 to 60 percent carbohydrates, and 25 to 30 percent fat, and you are eating enough calories, the body has a handle on how much fat it burns and typically doesn’t use or produce ketones. However, if you fast—which is the quickest way to enter into a state of ketosis—or if you severely restrict your carbohydrate intake, ketosis is the result.

Two other ways your body can enter ketosis is to exercise for a prolonged period or uncontrolled diabetes, which can become dangerous, even deadly. In fact, ketosis is a mild form of ketoacidosis, which most often affects people who have type 1 diabetes. Ketoacidosis is the main cause of death among diabetics younger than 24 years old.

The brain’s natural source of energy is sugar. According to basic biochemistry, “Glucose is virtually the sole fuel for the human brain, except during prolonged starvation.” Because the brain does not have an ability to store fuel, it “requires a continuous supply of glucose.” The keto diet does not provide that glucose.

According to the Center for Nutrition Studies, “ketosis is an adaptive state that allowed our ancestors to survive temporary food shortages.” When they faced inadequate food supplies, their bodies began to break down fat stores so they could survive. Because our ancestors did not consume a low-carb, high-fat diet normally, they did not have to deal with diet-induced ketosis.

It’s important to emphasize that ketosis is a temporary state. As the Center for Nutrition Studies notes, “ketogenic diet proponents advocate that we should aim to keep ourselves in a permanent state of ketosis, something that is completely foreign to human experience.”

However, as a short-term measure, ketosis may be helpful for losing weight. Ketones also can help suppress the appetite, enhance mental clarity, and lower the risk of several chronic diseases, including diabetes. Whether ketosis and these benefits are sustainable in the long-term is still a source of debate and controversy.

How to figure carb intake

Since restricting carbohydrates is a central theme of the keto diet, many people worry they will spend much of their time calculating these macronutrients. Fortunately, it’s a simple matter of subtraction.

Basically, on the keto diet you are limited to just 20 to 30 net grams of carbs per day. The term “net carbs” refers to the amount of carbohydrates that remain in a food once the dietary fiber has been subtracted. That’s because fiber is not digested by the body once you consume it, so the fiber grams don’t count toward your daily intake of carbs.

For example, a medium apple contains 25 grams of carbohydrates. When you subtract the 4.4 grams of fiber, you are left with about 19 grams of carbs. If you eat an apple, you are already near your limit of carbs for the day.

One cup of avocado, on the other hand, contains 12 grams of carbs. When you subtract the 10 grams of dietary fiber, you are left with a mere 2 grams of carbs. This is why avocados are considered a prime keto diet food, as well as the fact that it is packed with healthy fats, vitamins, and minerals.

Fortunately, if you use recipes from any of the countless numbers of cookbooks, websites, and articles on the keto diet, many of them provide the carb counts so you don’t have to worry. Nutrition labels on foods also are required to state the number of carbohydrates and fiber so you can always quickly calculate your intake from them.

Keto diet and weight loss

Weight loss is by far the most popular reason why people want to try the keto diet. Yet even though this is why so many individuals are jumping on this band wagon and many people swear they are losing pounds, experts and critics don’t agree on the success or safety of the weight loss claims.

Cimperman and other experts say that most of the lost pounds are due to lost water weight. This, however, is common with many weight loss diets. According to Cimperman, once the body is in a state of ketosis, you not only lose weight but muscle mass and tone. You also will suffer with extreme fatigue and eventually it will become more difficult to lose weight.

Keto diet and diabetes

The keto diet is often touted as a good choice for people who are living with type 2 diabetes. That’s because the diet not only can help people drop excess pounds, but it also improves insulin sensitivity, which helps keep blood glucose levels better regulated.

But according to some experts, including Academy of Nutrition and Dietetics spokesperson Lisa Cimperman, RDN, who also is a clinical dietitian at University Hospitals Case Medical Center in Cleveland, Ohio, the keto diet is the not the best eating plan for this group of individuals. She points out that while anyone with type 2 diabetes can benefit from the improved insulin sensitivity and weight loss associated with a low-carb diet, “there are many other ways to do it besides a fad diet that won’t keep weight off long-term.”

Read about the worst and best foods for a keto diet

Foods you can eat

It will come as no surprise that many of the foods you are allowed to eat on a keto diet are high in fat and are therefore animal-based. However, there are some low-carb fruits and vegetables allowed that can help you diversify your menu. Here are the foods you can eat on a keto diet:

  • Meats: Beef, chicken, turkey, pork, ham, bacon, lamb, organ meats. These should be grass-fed, pasture-raised, pesticide-free and hormone-free
  • Fatty fish: Salmon, tuna, mackerel, trout, shrimp, herring, cod, catfish, halibut, haddock. These should be wild-caught
  • Eggs: Focus on organic or omega-3 whole eggs
  • Butter and cream: Look for butter and cream from grass-fed cows when possible and whole fat
  • Plant-based beverages: So-called plant milks such as those made from almonds, hemp, rice, coconut, soy, cashew, and flax are all super low in carbs
  • Cheese: choose unprocessed cheeses, such as goat, blue, cheddar, or mozzarella
  • Fruits: avocados (yes, they are a fruit), olives, strawberries and other berries, grapefruit and other citrus (limited amounts)
  • Healthy oils: Mainly extra virgin olive oil, avocado oil, coconut oil
  • Low-carb vegetables: Enjoy all of the green leafy veggies such as kale, collards, mustard greens, chard, arugula, lettuces, spinach, chicory, turnip greens, and endive, as well as tomatoes, onions, bell peppers, broccoli, Brussels sprouts, cauliflower, eggplant, cucumbers, asparagus, green beans, mushrooms, zucchini, cabbage, and celery
  • Seeds and nuts: Almonds, flax seeds, chia seeds, pumpkin seeds, walnuts, Brazil nuts, pecans, chestnuts, sunflower seeds
  • Condiments: Stay with salt, pepper, herbs, and spices, unsweetened mustards and hot sauces, apple cider vinegar, soy sauce, pickles

Foods you need to avoid

Because carbohydrate intake must be kept to a bare minimum, the foods you need to avoid are those that have moderate to high levels of carbohydrates. They include the following:

  • Any sugary food: Fruit juices, cakes, cookies, candy, ice cream, chocolate, soft drinks, pastries, and similar foods
  • Starches and grains: Foods made from wheat or other grains/cereals, such as amaranth, barley, buckwheat, couscous, farro, millet, oats, quinoa, rice, rye, sorghum, and wheat, among others. Those foods include pasta, breads, rolls, bagels, and other baked goods, as well as crackers, chips, pancakes, waffles, cereals
  • Beans and legumes: beans (adzuki, fava, black, white, pinto, red, kidney, soy, navy), peas, lentils
  • Fruit: All fruits except small amounts of berries and citrus
  • Root and tuber vegetables: Carrots, beets, parsnips, turnips, potatoes, sweet potatoes
  • Diet and low-fat foods: These are highly processed and typically high in carbohydrates
  • Condiments and sauces: Most contain unhealthy fats and sugar unless you make your own. Read the labels
  • Sugar-free diet foods: They are highly processed and typically contain sugar alcohols, which can affect ketone levels.
  • Unhealthy fats: These include processed vegetable oils, which contain linoleic acid, an omega-6 fatty acid that has been associated with obesity and inflammation. These vegetable oils include corn, canola, soybean, peanut, sunflower, safflower, cottonseed. Also avoid unhealthy fats found in mayonnaise and similar salad dressings
  • Alcohol: Most but not all alcoholic beverages have a high carb content. An occasional low-carb beer may be allowed

Keto vs Atkins diet

The keto diet and Atkins diet share some characteristics, but there are also some major differences. Let’s start with a similarity. Both severely limit the intake of carbs, but the keto diet sustains that restriction while the Atkins diet keeps you in ketosis only until you are within about 15 pounds of your target weight.

After that, on the Atkins diet you can increase your carb intake up to 50 grams daily until you’re about 10 pounds away from your goal weight. That’s when you enter the next phase, when you can increase carb intake to about 50 to 80 grams daily. You are looking for the carb intake level that allows you to maintain your weight.

Once you have identified that level and maintain it for 30 days, you enter the last phase of the Atkins diet: maintenance. You can eat up to 100 grams daily as long as you don’t gain weight. You may need to make adjustments to your carb intake to achieve your maintenance goal.

Keto diet vs paleo diet

Both of these diets are popular, so let’s compare them. The paleo diet (aka, caveman diet) is based on the idea that we should be eating foods as close as possible to what the earliest humans ate because the current food production and processing methods are harmful to our health.

To that end, those who follow the paleo diet are told to avoid eating any processed sugar, most dairy foods, all grains and legumes, and of course, any processed foods at all. That leaves the following foods:

  • Meat, fish, eggs, seeds, nuts, fruits, and vegetables (not corn, however, which is a grain).
  • Certain oils and fats are allowed, including coconut, avocado, and olive oils, tallow, ghee/butter, and lard.
  • Sweeteners that are minimally processed, including raw honey, coconut sugar, raw stevia, and maple syrup
  • In addition, the paleo diet emphasizes that you should adopt healthy lifestyle practices such as exercise and stress management as well as always consider the environmental impact of your food choices

The keto diet, on the other hand, focuses on shifting your body’s dependence from carbohydrates to fat for energy; that is, a state of ketosis. Your food choices are limited and it’s necessary to strictly follow the diet in order to stay in ketosis.

The keto diet has the potential to help you lose weight in the short-term and improve blood glucose control. The paleo diet is less restrictive and thus easier to follow, yet it does not guarantee you will lose weight.

Keto diet vs low-carb

The concept of a diet is keeping your carbohydrate intake low (around 75 to 150 grams daily), which is high enough to avoid full-blown ketosis and will keep you feeling adequately energized. It is possible you can slip into a mild ketosis state between meals or if you exercise more than usual or during a fast. The keto diet, however, restricts carb intake to less than 50 grams daily.

Many people feel better physically and mentally if they eat more than 50 carbs daily yet still regulate their intake. If so, then a low-carb diet may be for you versus a keto approach. It’s a personal choice.

Supplements for keto diet

Some experts recommend taking supplements if you are on the keto diet because the restrictions of the diet are associated with a few significant drawbacks. Loss of muscle mass, for example, can be worrisome to some who try the diet, as well as diarrhea, keto flu, nutritional deficiencies, and a higher risk of serious health problems (see “Side effects of the keto diet”).

To help alleviate these and other side effects, you can take supplements. Here are some of the supplements you should consider taking. You also may want to talk to your healthcare provider about taking a blood test to determine your levels of these nutrients.

  • Magnesium: Because this critical mineral is found in foods such as whole grains, beans, and bananas, you may find yourself magnesium deficient, unless you are a fan of green leafy veggies such as spinach and kale as well as sunflower and pumpkin seeds. To at least meet the recommended daily intake (310 to 320 mg) of this mineral, a magnesium supplement may be in order.
  • Calcium: Dairy foods are a primary source of calcium for many people, yet many dairy products are banned from the keto diet. Other sources of calcium include green leafy vegetables and sardines with bones, which are acceptable in the keto diet. However, if these foods are not among your regulars, you may need a calcium supplement.
  • Iron: Iron may be a problem if you do not eat much beef, oysters, and fish. In addition, vegans and vegetarians who try the keto diet may need to supplement with iron. Monitor your iron intake and talk to your healthcare provider if you think you may need supplementation.
  • Vitamin D: Many people are low or deficient in vitamin D, even if they are not on the keto diet. If you get about 15 minutes of sunlight exposure daily and eat keto-approved foods containing vitamin D, such as egg yolks and fatty fish (e.g., sardines, tuna), you may get enough. However, check with your doctor to be sure you are not vitamin D deficient, since this is a critical vitamin for bone health, the heart, mood, and other needs.
  • Fiber: Since so many high-fiber foods are banned from the keto diet, there’s a good chance you will need a fiber supplement to support good digestion and intestinal health. Limited fiber intake also increases your risk of heart disease, colon cancer, obesity, and high cholesterol. Evaluate your fiber intake and consider a fiber supplement.
  • Digestive enzymes: The high fat content of the keto diet can be a shock to the digestive system. This shock can result in bloating, gas, nausea, and diarrhea. For some people, the amount of protein is higher than what they are used to, which also can cause distress. To help relieve these symptoms, you can consider taking a digestive enzyme supplement that contains lipases (breaks down fat) and proteases (breaks down proteins). A supplement that contains both types of enzymes would be most helpful.

Side effects of the keto diet

The keto diet is associated with both short-term and long-term side effects. Here are the most common ones, and you may be especially unhappy about the first three.

  • Regained weight. Regaining lost weight is nothing new to people who have tried diets before, and the keto diet is no exception. In fact, because the diet is so limited, the chances of regaining lost weight is especially great. In fact, regaining weight is “an issue with any fat diet, but it seems to be extra common with ketosis,” according to Kristen Kizer, RD, a nutritionist at Houston Methodist Medical Center. Kizer believes the keto diet is appealing to people who struggle with binge eating and portion control, and that this diet is not the answer to their problems. “In many cases, what they really need is a lifestyle coach or a professional counselor to help them get to the bottom of those issues.”
  • Reduced metabolism and loss of muscle mass. These two factors are related, and here’s why. Muscle burns calories more than fat, so the more muscle mass you have, the higher your metabolism rate. However, if you lose weight with the keto diet, you may be losing muscle mass and your metabolism rate will suffer. To make the situation even more distressing, when you go off the keto diet and regain weight, you are likely to regain fat and not muscle. This affects your resting metabolism rate and your ability to burn calories.
  • Higher risk of heart disease and diabetes. This side effect is particularly troubling. If people do the keto diet right—which many experts such as Josh Axe and Stephanie Estima, MD, say is mostly plant-based with small amounts of lean animal protein and fair amounts of healthy fats—then these risks can be avoided. However, for those who use the keto diet as an excuse to chow down on steaks, bacon, butter, and cream, the diet can result in elevated cholesterol and a higher risk of diabetes.

At the European Society of Cardiology Congress in Germany, the authors of a 25,000-person study reported that people who were on the lowest-carb diets had the greatest risk of dying from cardiovascular disease, cancer, and all other causes. The experts concluded that “this study adds to the growing body of evidence showing the harmful long-term effects of a low-carbohydrate diet.”

In another study, researchers found that people who were on low-carb diets that were high in animal proteins had a greater risk of early death when compared with those who ate carbs in moderation. However, the opposite was true among people on low-carb diets who chose plant-based proteins over meat and dairy foods.

  • Keto flu. Within a few days of starting the keto diet, some people what is commonly called the keto flu, which can involve vomiting, gastrointestinal distress, lethargy, and extreme fatigue. According to natural medicine physician and clinical nutritionist Josh Axe, about 25 percent of people who try the diet experience these symptoms. He notes that the symptoms occur when the body doesn’t have any sugar to burn for energy and begins to burn fat. This switch can cause fatigue and other symptoms that last for a few days.

Symptoms of keto flu can be reduced by getting lots of sleep and drinking plenty of water. Some people turn to natural supplements for help, including adaptogenic herbs such as ashwagandha or ginseng, or drinking matcha green tea.

  • Switching to a keto diet can cause diarrhea for several reasons. One is a lack of fiber in the diet. If you don’t eat enough vegetables, which are rich in fiber, and focus instead on animal foods, then diarrhea is a possibility. Another reason may be the gallbladder is working overtime to process the high fat in your diet. Yet another possibility may be an intolerance to dairy foods.
  • Anyone who has either type 1 or type 2 diabetes should not adopt the keto diet unless they discuss it with their doctor and remain under close supervision. Individuals with diabetes who enter ketosis can easily slip into ketoacidosis, which can result in liver, brain, and kidney damage, and even death.

Ketoacidosis can also occur in people who don’t have diabetes, although this complication is rare. Symptoms of ketoacidosis include frequent urination, nausea, bad breath, breathing problems, and dry mouth. If you experience these symptoms while on the keto diet, call your doctor immediately.

Due to the popularity of the keto diet, there is a wealth of recipe ideas available. You might begin by checking out Dr. Mercola's keto recipes or some vegetarian and vegan keto diet recipes.

Bottom line: is keto right for you?

No one diet is right for everyone, and that includes the keto diet. Ask yourself: What do I want to accomplish with this diet? Does it fit into my lifestyle? Is it sustainable? Is it a healthy choice for me in the long run? Do I understand the possible side effects? Have I considered other diets that have been shown to help with weight loss and provide other health benefits as well?

Once you have answered these questions—and perhaps others you want to add—then you can decide which direction you want to go. Fortunately there are many articles on the topic of the keto diet, but be sure to look for those with scientific evidence. You may also want to discuss your questions and concerns with a knowledgeable healthcare professional.

For more information on the keto diet as well as recipes, be sure to subscribe to our newsletter:

Read This Next: The Best and Worst Foods for a Keto Diet: Know What You Need to Eat

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Baum K. 5 supplements you should take if you’re on the keto diet. Health 2018 Nov 15
Berg JM et al. Each organ has a unique metabolic profile. Section 30.2. Biochemistry, 5th ed. New York: WH Freeman, 2002.
The ketogenic diet: a detailed beginner’s guide to keto. Healthline
European Society of Cardiology. Caution against cutting down on carbohydrates. 2018 Aug 28
MacMillan M. 7 dangers of going keto. Health 2018 Oct 30
Seegert L. The keto diet is gaining popularity but is it safe? Healthline 2016 Jun 7
Seidelmann SB et al. Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. The Lancet Public Health 2018 Sep 1; 3(9): Pe419-28
Chuter R. Is the ketogenic diet natural for humans? Center for Nutrition Studies 2019 Jan 17
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Deborah is a freelance health writer who is passionate about animals and the environment. She has authored, co-authored, and written more than 50 books and thousands of articles on a wide range of topics. Currently, she lives in Tucson, Arizona.