What is the Keto Diet?


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Does the keto diet deliver, or is it just another fad diet creating a lot of hype?

Several different keto-friendly foods allowed

The keto diet, short for the ketogenic diet, is a very low carbohydrate, high-fat diet. It may seem relatively new, but it has been used in medicine for about 100 years to treat epilepsy. In the 1970s, it gained popularity as a weight-loss diet by Dr. Atkins. The Atkins diet starts with a strict ketogenic phase.

The ketogenic diet has gained even more popularity today for its many potential health benefits. In addition to epilepsy management and weight loss, research shows the keto diet may protect against diabetes, cardiovascular disease, mood disorders, and several neurological diseases.

How does the keto diet work?

The keto diet drastically reduces carbohydrates and replaces them with fat. When carbohydrate intake is low enough, the body starts to burn fat for fuel. The liver can convert stored body fat (adipose tissue) and dietary fats into molecules called ketones (ketone bodies). This is where the diet got its name. The body and brain use ketones for fuel instead of blood sugar (glucose) – carbohydrate. Beta-hydroxybutyrate (BHB) and acetoacetate (ACAC) are important ketones used by the body.

When carbohydrate intake is low enough, the body starts to burn fat for fuel.

Over time, usually a few consecutive weeks, the body will adapt to using ketones for fuel. The cells change the way they work biochemically, and the body becomes efficient at using fat and ketones. This state is often referred to as keto-adaptation or fat-adapted. Insulin levels, inflammation, and oxidative stress (cell damage from an imbalance in antioxidants to free radicals) decrease, leading to many health benefits seen with the keto diet.

What is ketosis?

The body is said to be in “ketosis” when blood ketones increase to levels between 0.5 and 2 mmol/L. You can measure ketone production at home using a medical device (e.g., Precision Xtra meter, Keto-Mojo meter). These meters are similar to a blood glucose monitor used by people with diabetes. Ketones can also be measured in the urine and breath. Still, blood is the most accurate and reliable method [1]. An increase in blood ketones occurs after a few days (to a couple of weeks) of eating 20-50 grams of carbohydrate per day and 1.2-2 grams of protein per kilogram per day.

Ketosis is a metabolic state in which there’s a high concentration of ketones in the blood. 

Protein intake is moderate in a ketogenic diet. This differentiates it from other low-carb diets that recommend high protein intake. The amino acids alanine and glutamine in protein can be converted to glucose. Therefore, high protein consumption can decrease ketone production and take you out of ketosis.

The 1.2-2 grams per kilogram per day range will help you stay in ketosis and maintain lean body mass (e.g., muscle mass). Keeping protein intake moderate and adding just enough carbohydrate to provide critical nutrients from plants (vegetables, berries, nuts, seeds) is an essential part of a well-designed ketogenic diet. The amount of carbohydrate and protein varies a bit.

Some people can consume a little more carbohydrate and/or protein and stay in ketosis. Measuring ketones can help you set an individualized range.

People sometimes confuse ketosis with ketoacidosis. Nutritional ketosis from a ketogenic diet should not be confused with ketoacidosis, a life-threatening complication in type 1 diabetics.

Variations of the keto diet

There are a few variations of the keto diet. We’ll briefly look at three – classic, modified, and MCT.

The classic ketogenic diet model developed at the Mayo Clinic to treat epilepsy uses a 4:1 ratio of fat to protein plus carbohydrate (90% fat, 6-8% protein, and 2-4% carbs). This version is the most restrictive [2, 3, 4].

Luckily, there are less restrictive variations of the classic model. A modified ketogenic diet (modified Atkins diet) created at Johns Hopkins Hospital allows higher protein intake. Compared to the classic ketogenic diet, the modified version typically has a 2:1 or a 1:1 ratio of fat-to-carbohydrate and protein (65% fat, 30% protein, 5% carbs). This more flexible design is easier to stick with and reduces the risk of nutritional deficiencies and digestive discomfort [1]. The initial carbohydrate consumption is approximately 10–15 g per day. After 1-3 months, carbs may increase to 20 g per day [3]. The goal, of course, is to stay in ketosis.

Supplementing with medium-chain triglycerides (MCT) can also increase flexibility in the diet. MCT is a type of fat that produces ketones more quickly than long-chain fats found in meat, milk, eggs, and many vegetable oils. Some people supplement their keto diet with coconut oil because it contains 62%-70% MCT [5]. There are MCT products (oil, powder) on the market too. They typically contain one or two types of medium-chain fats to support fast absorption. Because MCT increases ketones, supplementing with this fat allows you to eat a little more carbohydrate and protein (35% fat, 20% protein, 35% carbs) and stay in ketosis.

Unfortunately, there is a drawback. MCT can cause digestive discomfort (cramping, bloating, diarrhea) in some people [3]. Starting with small amounts of MCT, such as a teaspoon, and gradually increasing it can help reduce these symptoms. Results are best when MCT is evenly divided and consumed with each meal [6].

5 health benefits of the keto diet

#1) Brain health

Growing evidence suggests the keto diet can help manage several neurological disorders in children and adults. The keto diet has been used to treat epilepsy for a century. More recently, it has been used to manage other neurological disorders such as Alzheimer’s disease and migraine headaches. And the research looks promising.

Evidence shows the keto diet can reduce the number of seizures and protect the brain cells (neurons) from being damaged by a seizure [2, 8]. Several studies have shown enhanced short-term cognitive performance (attention, memory, language) in patients with Alzheimer’s disease following very restricted carbohydrate intake and those using MCT [2].

The keto diet has been shown to reduce migraine headache attack frequency and intensity, although improvements taper off. Chronic cluster headache may also benefit from a keto diet. Studies have found reduced frequency and, in some cases, full resolution of headaches [2].

Although neurological disorders differ significantly, they appear to have distinct underlying pathologies – disrupted energy metabolism, oxidative stress (imbalance of antioxidants and free radicals), and neuro-inflammation. The keto diet improves each of these. Although carbohydrate has been considered the brain’s primary fuel source, the keto diet appears to provide more high-energy molecules (e.g., ATP) than a high carb diet. This helps reduce free radical damage.

Ketones have been shown to protect neurons against injury. The keto diet also alters brain chemicals called neurotransmitters like gamma-aminobutyric acid (GABA), which helps reduce overly excited areas of the brain [8, 2].

Recent research is looking at the keto diet’s role on gut bacteria, brain-derived neurotrophic factor (BDNF), and autophagy. It may be that changes in the gut bacteria are protecting both the gut and brain. The ketone BHB has been shown to increase BDNF, which acts like Miracle-Gro for the brain. Autophagy may lead to neuroprotective benefits of the keto diet as well. Simply put, autophagy is the process of cellular cleansing. Unnecessary or dysfunctional components of the cell are removed [9, 8, 2].

#2) Mood

The keto diet may help treat mood disorders like depression. Although there isn’t much clinical research yet, case reports and preclinical studies show mood-stabilizing and antidepressant effects of the diet. Increased ketones (e.g., BHB), increased GABA levels, improved ATP production, reduced oxidative stress, improved insulin function, and reduced inflammation support a healthy mood state. 

Research shows depression is associated with low GABA levels, lower ATP levels, lower antioxidant levels, higher free radicals, increased oxidative stress, insulin resistance, and increased inflammation. Hence, the keto diet helps improve many factors associated with depression [10, 11, 8, 2, 12].

It is important to follow a well-designed keto diet. Nutrient deficiencies can worsen mood and increase the risk of depression. Reduce processed foods that can increase inflammation. Eat plants (nuts, seeds, leafy greens) and incorporate healthy fats (olive oil, fish/fish oil). These foods will provide nutrients that reduce oxidative stress and inflammation and support a healthy mood state.

#3) Weight management

A keto diet supports weight management. Numerous studies have shown improvements in obesity in those following a carb restrictive diet. In fact, a keto diet appears to accelerate weight loss compared to a low-fat diet. Several studies have seen greater weight loss and fat loss in keto diets than low-fat and Mediterranean diets [source 13, 14, 15].

The keto diet’s many metabolic changes support weight loss—the body shifts to using fat, including body fat, for fuel. Hunger and cravings are often reduced dramatically, leading to reduced food intake. Researchers believe this is due to increased ketones. Studies have also seen changes in appetite control hormones like ghrelin. Ghrelin is often called the hunger hormone. Ghrelin levels appear to decrease in people following a keto diet. As signals to eat are dampened, cravings often decrease [16].

#4) Diabetes support

Growing research suggests low carb eating patterns may help prevent and manage type 2 diabetes. Type 2 diabetes is characterized by elevated blood sugar and impaired insulin function. Studies are finding improvements in insulin sensitivity, reduced blood sugar, and weight loss in people following a ketogenic diet [17].

Greater insulin sensitivity means your cells are more responsive to insulin and can get glucose (blood sugar) out of the bloodstream and into the cells. This reduces damage to the body. Weight loss is an important benefit of the keto diet. There is a strong association between obesity and type 2 diabetes.

One study found greater improvements in hemoglobin A1c (average blood sugar over 2-3 months), weight loss, and HDL-cholesterol (protective cholesterol) in study participants on a ketogenic diet compared to a low glycemic index diet. Foods with a low glycemic index release glucose slowly and steadily. 95.2% of the keto diet group reduced or eliminated diabetes medication compared to 62% of people on the low glycemic index diet [18].

Another study compared a keto diet (20-50 g carbohydrate excluding fiber) with a moderate carbohydrate diet (45%-50% of total calories). Researchers followed the participants for 1-year. The keto group decreased A1c, lost more weight, and had greater reductions or elimination of diabetes medication than the moderate-carb group [19, 20].

#5) Cardiovascular health

The keto diet protects the cardiovascular system in quite a few ways. Several studies have shown reduced cardiovascular disease (CVD) risk factors in people following a keto diet, including weight loss, reduced body fat, increased HDL-cholesterol (good cholesterol), improved total cholesterol/HDL-cholesterol ratio, reduced triglycerides, improved triglyceride/HDL-cholesterol ratio, improved blood pressure, improved blood sugar, and reduced inflammation. And, heart medication dosage has been reduced in some individuals [21, 22, 19].

The American Health Association and American College of Cardiology developed the aggregate cardiovascular disease risk score (ASCVD) to estimate 10-year and lifetime risks for atherosclerotic (plaque in the arteries) cardiovascular disease. This score is based on the combination of cholesterol (total, HDL, LDL), systolic blood pressure, diabetes history, medication use, age, gender, and race.

A one-year clinical trial found keto diet participants reduced the risk of having a heart attack or stroke by about 12% [19]. A meta-analysis study (a statistical analysis that combines results from multiple studies) showed a better 10-year ASCVD risk score in low-carb dieters compared to low-fat dieters [23, 13, 24]. 

Ketogenic and low-carb diets appear to reduce inflammation [25]. Inflammation is a powerful cardiovascular disease risk factor. It plays a key role in many chronic diseases (diabetes, depression, anxiety, Alzheimer’s disease, cancer). High-sensitivity C-reactive protein (hsCRP) is often used to measure inflammation. One study found a 39.3% reduction in hsCRP in participants following a ketogenic diet for 1-year [19]. Another 2-year low-carb study found a 29% reduction in hsCRP [15]. These reductions are impressive! Some cholesterol-lowering medications known for their ability to reduce hsCRP don’t come close to this [26].

What kind of food can you eat?

A well-designed keto diet should provide a variety of high-quality foods to maximize nutrition, including healthy fats, protein, and carbohydrates. This will increase vitamins, minerals, antioxidants, and fiber.

  • Meat: beef, chicken, pork, bacon, lamb (grass-fed and free-range when possible)
  • Eggs: omega-3 enriched, pastured
  • Fish: salmon, tuna, sardines, mackerel, shrimp
  • Nuts and seeds: almonds, macadamia, walnuts, chia seeds, pumpkin seeds
  • Full-fat dairy: butter, cheese, cream, cream cheese, Greek yogurt (watch the carbs)
  • Healthy oils: extra virgin olive oil, coconut oil, avocado oil
  • Low-carb vegetables: leafy greens, broccoli, asparagus, cauliflower, tomatoes, onions
  • Low-carb fruit: avocados, raspberries, blackberries, strawberries, blueberries, olives 
  • Replenish fluids and sodium: bone broth or a couple of bouillon cubes

What should you limit/avoid?

  • Sugar and refined carbs: soft drinks, candy, ice cream
  • Grains: bread, cereal, rice, pasta
  • High carb vegetables/starches: potatoes, sweet potatoes, parsnips, turnips
  • High carb fruit: bananas, apples, grapes
  • Legumes: beans, lentils
  • Alcohol: wine, beer, mixed drinks
  • Inflammatory/unhealthy fats: soybean oil, corn oil, trans fats/hydrogenated fats (in processed foods)
  • Be careful when adding artificial sweeteners. Some popular sugar substitutes like sorbitol and other sugar alcohols (xylitol, maltitol, erythritol) can cause gastrointestinal distress, especially in people with IBS or IBD (e.g., colitis, Crohn’s disease). Additionally, artificial sweeteners can negatively impact the gut bacteria and increase sugar cravings.

Are there rules?

Many people like the keto diet because it’s pretty straight forward. You don’t need to combine certain foods or count calories. Although keeping calories in check if you want to lose weight is not a bad idea. There are three general rules:

  1. Drop your carbs to between 20-50 grams per day.
  2. Eat protein in moderation (1.2-2 grams/kilogram body weight).
  3. Eat a lot of fat.

Tracking your carbs will help you keep them in check. Some apps make this easy (e.g., MyFitnessPal).  

How you might divvy up your daily carbs

Carb Food Source Grams Per Day Foods
Protein-Based Food 5-10 grams Eggs, half and half, yogurt, processed meats, some cheese (shredded)
Vegetables 10-15 grams Asparagus, broccoli, celery, cucumber, cauliflower, eggplant, green beans, leafy greens (kale, spinach), mushrooms, onions, peppers, radish, snow peas zucchini
Nuts & Seeds 5-10 grams Nuts (almonds, Brazil, hazel, macadamia, pecans, pine, walnuts), nut butter, seeds (chia, flaxseeds, hemp, pumpkin, sunflower)
Fruits 5-10 grams Avocados, blueberries, raspberries, strawberries, olives, tomatoes, V8 juice
Miscellaneous sources 5-10 grams varies

Source: The Art and Science of Low Carbohydrate Performance

How long should you be on the diet?

It is difficult to recommend how long to stay on a keto diet. There are not many long-term studies. Most studies last from weeks to one or two years. Some of the longest studies have been conducted on people with epilepsy lasting up to 10 years and showing positive effects [27, 28]. More long-term studies are needed to confirm this.

Consider sticking with the diet for at least a few months. It takes time to become proficient with the diet and for your body to become keto-adapted. After settling into the diet, see how you feel emotionally and physically. Are you sleeping well? How is your energy level? Do you have good mental clarity and emotional wellbeing? The keto lifestyle may or may not be a fit for you.

What is the best way to get started on the keto diet?

  • Plan!  Don’t start your new lifestyle until you have food to support this way of eating. If all you have in your house is cereal, bread, and pasta, you’re going to struggle – a lot! Go shopping and stock your kitchen with healthy keto-friendly foods. Be prepared.
  • Track Carbs.  Read food labels and/or use an app to track your carbs. You can track protein and fat too if you like. Rather than tracking total carbs, many people count “net carbs,” also called impact carbs or digestible carbs. Net carbs are calculated by subtracting fiber from the total carbohydrate content. For example, a 1 ounce serving of almonds has 6 grams of total carbohydrate and 3 grams of fiber. This would give you three net carbs (6 – 3 = 3 NC). Fiber doesn’t negatively impact blood sugar levels, so it can be subtracted from your total carb intake [29].
  • Fasting. If you want to jump-start ketosis, consider fasting. Research shows fasting can help you get into ketosis more quickly. Even an overnight fast can put you into mild ketosis. The classic ketogenic diet used for epilepsy management sometimes requires a 24-48 hour fast before starting a diet [30]. 

Should you take supplements?

A well-designed keto diet with a variety of foods will provide a lot of nutrition. Still, there can be shortcomings, especially on a strict classical keto diet.

Supplementing with a carbohydrate-free multivitamin and mineral dietary supplement with trace minerals is important due to the limited amounts of fruits, vegetables, enriched grains, and calcium-containing foods. This is especially important for postmenopausal women. Currently, there is no strong evidence for any other dietary supplement [3, 31].

Dietary supplements can help you fill in dietary gaps, but they don’t give you everything whole food does. Including foods and beverages with antioxidant activity would be wise. Some vitamins, minerals, and phytonutrients act as antioxidants. The table below shows some low carb antioxidant-rich foods [32].

Antioxidant Keto-Friendly Food Sources
Vitamin C strawberries, tomatoes, broccoli, cauliflower
Vitamin E olive oil, nuts, peanut butter, seeds
Carotenoids carrots, tomatoes, spinach, Brussels sprouts, broccoli, winter squash
Selenium nuts, whole grains, seafood, meat

Phytonutrients are naturally occurring compounds found in plants that provide antioxidant protection and support health [33]. Adding herbs, spices, teas, and fats from plants is a great way to incorporate more phytonutrients and antioxidants into your keto diet.

  • Coffee
  • Coconut oil
  • Cinnamon
  • Cocoa powder (unsweetened)
  • Garlic
  • Green tea
  • Olive oil
  • Onion
  • Oregano
  • Peppermint (fresh)
  • Turmeric

Keto meal ideas

This one-day meal plan below provides approximately 50 Net Carbs (NC) and about 30 grams of fiber.

Breakfast (8.25 NC)

  • 2 fried eggs
  • 1 Tbsp butter (used to fry eggs and sauté vegetables)
  • 1 cup baby spinach
  • ¼ cup yellow bell pepper
  • 2 Tbsp chopped onion
  • 1 tsp balsamic vinegar

Snack (6.5 NC)

  • 1 cup sliced cucumbers
  • 2 Tbsp hummus

Lunch (11.5 NC)

  • Grilled chicken
  • 4 cups spinach salad
  • 2 slices cheddar cheese
  • ½ Haas avocado
  • 1 small tomato
  • 1 low carb pita
  • 2 Tbsp extra-virgin olive oil
  • 1 tsp balsamic vinegar

Snack (5.5 NC)

  • 1 oz walnuts
  • ¼ cup blueberries

Dinner (9 NC)

  • Baked salmon
  • 2 Tbsp Aioli or butter
  • ½ cup steam broccoli
  • 2 cups arugula
  • 5 cherry tomatoes
  • ½ cup sliced cucumbers
  • ¼ cup sliced almonds
  • 2 Tbsp Italian dressing

Dessert (10 NC)

  • 5 large strawberries
  • 4 Tbsp whipped cream (no sugar added)
  • Ghirardelli Intense Dark Square

Keto-Friendly recipes to try

Side effects and risks

Some people may experience a few adverse effects, which are usually mild and temporary. Typically, side effects improve as the body adapts or with minor adjustments (e.g., fiber, fluids, sodium) [31, 34].

  • Gastrointestinal Discomfort. Constipation and abdominal discomfort are the most common adverse effects. These negative side effects are often seen during the first few weeks of the diet and are mild in most people. Some people experience diarrhea. Again, this often occurs soon after making dietary changes and resolves in a few days to weeks. Diarrhea is often due to MCT supplementation. It may help to limit the amount of MCT oil or coconut oil used and increase it gradually. Eating a well-designed keto diet with fiber-rich nuts and vegetables can reduce many of these negative side effects. The Institute of Medicine recommends 25 grams of fiber per day for females and 35 grams for males 50 years of age and younger. A sugar-free fiber supplement may help you reach the recommended fiber intake [35, 31, 34].
  • Keto-flu.  Some people experience low energy, digestive discomfort, poor mental function, nausea, and even vomiting when they begin a keto diet. This has been labeled the “keto-flu” and often occurs when people don’t get adequate fluids and sodium. Because the kidneys don’t hold onto water the same way they do when eating high carbohydrate diets, we need more sodium (salt). Unless you have to restrict your sodium intake due to a health condition like high blood pressure, you will likely need a sodium boost. Adding two grams of sodium by drinking broth or bouillon will likely protect you from the keto-flu. Easing into the diet can also help reduce side effects [31, 34].
  • Keto Breath.  The ketone, acetone, gets excreted through the breath. It has a very distinct odor. Some say it smells like nail polish remover and has a metallic taste. Although it may be unpleasant, this too typically goes away once you are keto-adapted.
  • Increased LDL-Cholesterol (LDL). It is worth noting that LDL increases in some people following a ketogenic diet. This has been a concern because LDL is associated with an increase in cardiovascular disease risk. Today, however, there is growing research looking more deeply into LDL particle size. Some LDL particles are small and dense, while others are large and buoyant. The small dense LDL appears to increase atherosclerosis. In contrast, the larger particles appear to have a more neutral effect [36, 37]. A one-year study following type 2 diabetics on a well-designed ketogenic diet found a rise in LDL, but there was a positive shift in LDL particles away from the small dense LDL [19]. Additionally, the increase in LDL appears to be temporary [28].

Do certain people need to avoid the diet?

The keto diet is not for everyone. Some people simply don’t like eating a high-fat, low-carb diet, while others are at risk of life-threatening complications. A diet of mostly fat could lead to ketoacidosis (not nutritional ketosis) in a person that can’t metabolize fat properly.

The keto diet is contraindicated in people with pancreatitis, liver failure, fat metabolism disorders, primary carnitine deficiency, carnitine palmitoyltransferase deficiency, carnitine translocase deficiency, porphyrias, or pyruvate kinase deficiency.

People with diabetes taking insulin or hypoglycemic medications that put them at risk of hypoglycemia and those starting a keto diet with elevated LDL-cholesterol should be closely followed by a physician.

Take home message

Evidence shows the keto diet trend is not built solely on hype. The research is fascinating, compelling, and it’s growing. A well-designed keto diet can help manage several neurological disorders, improve mood, reduce cardiovascular disease risk, improve type 2 diabetes, and accelerate weight loss.

If you are intrigued by the keto diet, talk with your doctor, and keto-trained health professionals before getting started, especially if you have any health issues.

Jessica Gavin

I'm a culinary school graduate, cookbook author, and a mom who loves croissants! My passion is creating recipes and sharing the science behind cooking to help you gain confidence in the kitchen.

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13 Comments Leave a comment or review

  1. Marion says

    Jessica I follow you every day. I’ve been looking for information on the Keto diet. This was very helpful. Thank you.

  2. Cindy O. says

    Thank you! I respect you and have been going in the direction of a keto diet due to an apparent problem with my pancreatic function. (My opinion, not my doctor’s, who doesn’t believe me)! So all I have to work with is my diet and lifestyle. I’m grateful for all of the details you provided, especially that one can have 90% of their calories as healthy fat. I don’t eat nearly that much fat, but had been feeling uneasy about the larger than most people amount I do eat, until reading that in your column. No problems noted for me from eating lots of fat so far, fortunately. And don’t worry, I’m not going to consider yours medical advice. More like advice from a friend, which I can verify online if I ever want to. I’m doing what I hope will be a quick fix of my pancreas, not planning to draw it out for too long.
    Thanks for the timely-for-me article.
    Cindy O.

    • Jessica Gavin says

      Thank you for your feedback, Cindy! It’s always a good idea to follow up with your doctor about the diet, just to make sure the risk is low.


    Thank you for the information on the Keto diet. I have been on the diet for three weeks .Doing very well feel better & loosing weight.