Bellow is a very detailed and informative piece about the fundamentals of the ketogenic diet. As I have stated previously in my own articles, I do not recommend, promote or endorse any specific diets or products. In this case I found the information to be useful when discussing fasting and the different ways to achieve ketosis, as well as the difference between terms like “ketosis”, “ketogenic”, and “ketoacidosis”.
I always recommend people inform themselves before starting any new diet, exercise, or behavior change related to nutrition, and believe the best way to achieve ketosis is using a combination of intermittent fasting and consuming a healthy diet of mostly whole-food plant-based proteins and fats, with the right amount of complex carbohydrates.
The article was written by Nate Martins and Dr. Brianna Stubbs, and was published by HVMN on February 19, 2019. Please visit and support their website.
The keto diet has one goal: get the body producing ketones. From this, all the health benefits you’ve heard of—from weight loss to performance—trickle down. The question is…how do you get your body to begin producing ketones?
First, let’s talk basics. Ketones are a fundamentally different energy source than the carbohydrates and fats your cells typically use for energy. It can take several days (or weeks!) of ketogenic, low-carb, high-fat eating before the body starts to produce ketones. And the time it takes to get into ketosis varies between individuals.
“Keto” comes from the word “ketogenic.” This is a scientific term meaning that the body is producing ketones from fat.1 When blood ketone levels exceed 0.5mM, the body has achieved “ketosis.” Ketosis can be naturally achieved two ways: through diet or fasting (meaning the body is producing its own ketones), or also by consuming products that raise blood ketone levels. Ketosis and ketogenic are two different things; a body in ketosis doesn’t mean that body is ketogenic.
Ketogenic means the body is producing its own ketones, which must happen through diet or fasting. This body is in ketosis because blood ketone levels are over 0.5mM. Someone else may consume ketones through an external means. This body is also in ketosis because its blood levels are over 0.5mM, but it’s not ketogenic—because it’s not producing its own ketones. Simple enough, right?
Now that you know how to get your body into ketosis (through a low-carb diet / fasting), let’s explore the different ranges of ketosis and how to start a ketogenic diet.
Ways to Achieve Ketosis
As with all metabolic processes, the state of ketosis is a spectrum. Past a threshold (which varies from person to person), even a small increase in dietary carbohydrate intake can trigger enough insulin release to take the body out of ketosis.
General target blood ketones levels are as follows:
- No ketosis: under 0.5 mM BHB in blood
- Low ketosis: 0.5 – 1.5 mM BHB in blood
- Moderate ketosis: 1.5 – 3 mM BHB in blood
- High ketosis: over 3 mM BHB in blood
- Pathological ketosis: over 15 mM BHB in blood
Let’s explore how the body achieves ketosis.
The typical methods used to generate physiological levels of ketosis are fasting, the ketogenic diet, and consuming exogenous ketones.
After an overnight fast, a low amount of ketones (0.1mM – 0.2mM) can often be detected in the blood. As the time spent fasting increases, blood ketone levels slowly rise until a plateau at 8mM – 10mM of beta-hydroxybutyrate (or BHB, the predominant ketone body in the blood) has been reached after many days. Scientist Hans Krebs described this plateau as “physiological ketosis.”2
Fasting long-term is unsustainable, so following a strict ketogenic diet can be used to maintain a low level of continuous ketosis. Research suggests blood BHB levels between 0.4mM – 1mM can be achieved while following a ketogenic diet.3 Anecdotal evidence suggests it’s sometimes possible to reach higher levels.
The level of ketosis required for different physiological benefits is unknown. For endurance sports, a higher level of ketosis (>2mM) appears to be superior to lower levels.4,6 This is possible because ketones fuel athletes’ muscles during a workout. However, some other benefits of ketosis, such as reduced appetite may be seen at much lower levels (0.5mM).7
Sometimes, the body starts producing ketones as a result of a disease (pathology). This can lead to dangerous levels of ketones in the body, though these high levels are very uncommon in healthy people following the ketogenic diet.
Alcoholic ketoacidosis (AKA) is a result of chronic alcohol consumption usually accompanied by malnutrition. AKA is characterized by increased ketone production (levels > 15mM) via liver alcohol metabolism, in conjunction with a mild elevation in blood glucose levels. Symptoms include nausea and vomiting, fatigue, altered breathing, and abdominal pain.8
Diabetic ketoacidosis (DKA) occurs most frequently in patients with type 1 diabetes. DKA is the simultaneous occurrence of high blood ketones (> 20mM), high blood glucose, and acidification of the blood. It develops when insulin is absent, or insulin signaling is no longer functional. This means the physiological state of starvation is triggered, even in the presence of high blood glucose. As during starvation, lipolysis (fat release) increases. This causes the liver to produce a high amount of ketones and blood pH to fall (as ketones are an organic acid).
As glucose levels are very high, the excess is excreted in the urine. This draws water and electrolytes out of the body, causing dangerous dehydration. Symptoms of DKA include nausea, vomiting, altered breathing, abdominal pain, and unconsciousness. The rapid onset and alarming nature of DKA is a reason why ketosis has a bad stigma in the medical community.
Starting a Ketogenic Diet
The keto diet is a moderate-protein, low-carb, high-fat diet. Its goal is to get the body to produce ketones, which are then used an fuel source for both the brain and the body. But because it’s low-carb, high-fat, the keto diet often gets confused with other diets out there.
What Makes Keto Unique?
Just because a diet is low carb doesn’t mean it’s keto. The subtle differences in macronutrients on keto make it unique (more on these later). Keto isn’t Atkins. Keto isn’t paleo. Keto isn’t high protein.
Usually, keto is confused with Atkins. On Atkins, the initial aim is to restrict the carbohydrate intake to less than 20g per day. This degree of restriction is likely to lead to ketosis, although this is not an explicit aim. Then, the diet reintroduces carbohydrates to a level “the body can tolerate.”9 There’s also less restriction on protein compared to a true ketogenic diet: high fat, moderate protein, low carbohydrate.
Tips for Starting a Keto Diet
Don’t try to start the diet gradually. If carbohydrate intake is moderately-low, blood sugar levels may not be enough to fuel the brain, and the presence of carbohydrate in the diet might still be enough to stop the body from making ketones.
The main objective when starting the ketogenic diet is to restrict carbohydrates to 20 digestible grams per day or less (this is what’s considered a strict ketogenic diet) and consume fat until you’re satiated. Remember to consume plenty of fiber as well. And regarding protein: stay at or below 0.45 grams of protein per day, per lb of body weight (1g/kg). If your goal is to lose weight, aim for 1 gram of protein per kg of your target weight.
Here are a few tips for when you’re starting keto:
- Make a keto meal plan. It’s a good idea to establish an eating plan before starting the diet. Make a shopping trip to stock up on a range of foods that are low in carbohydrates and high in fat
- Use an app to track macronutrient intake. Apps such as MyFitnessPal are great to get an idea of the macronutrients in common foods. There is also a range of special online keto diet calculators
- Search for a few keto recipes to adapt cooking methods. Due to the high-fat consumption required to get into ketosis, it may be beneficial to change daily staples or cooking methods. You could increase your intake of tasty foods such as coconut oil, heavy cream, and cheese
- Make an approved list of keto diet foods and eliminate carbohydrate-rich foods. It will be easier to follow the diet by throwing out any foods to avoid. It’s recommended to check the labels for hidden added sugars
- Consider starting a ketogenic diet with a short period (16-36 hours) of fasting (consuming zero calories). Fasting depletes carbohydrate stores and can accelerate ketone production
- Gentle cardio exercise (~30 minutes) or some short high-intensity intervals (10-second sprints) can deplete carbohydrate stores and speed up ketone production
Keto Diet for Weight Loss
The ketogenic diet can be used to help with weight loss.
Recently, the number of positive keto diet reviews, and small-scale science studies has increased. The rising popularity of the diet has led to a demand for further randomized control trials to study its long-term efficacy. A key reason why the ketogenic diet helps weight loss is that it decreases hunger. This makes it easier to maintain a calorie deficit. It is important to stress that the overconsumption of calories will generally prevent weight loss, regardless of the macronutrient composition.
Cyclical Ketogenic Diet and Cheating on Keto
At the moment, there is not a clear answer as to whether the benefits of the ketogenic diet can be achieved by cycling on and off the diet. It’s best to stick to the diet for one or two months minimum to see benefits. It can take several days to get into ketosis1 and 3-6 weeks to become “fat adapted.”3
Some research indicates ~40 days on the ketogenic diet interspersed with periods of healthy eating with more carbohydrates (Mediterranean diet) could maintain weight loss.10
“Cheating,” and consuming high-carbohydrate food, quickly stops ketone production by the liver. It can then take a considerable amount of time for the body to get back into ketosis. Time taken to get back into ketosis will depend on many factors including, the amount of carbohydrates consumed, how adapted the body is to produce ketones, activity level, etc.
However, cyclical ketogenic diets are a promising area of scientific investigation. Recently, scientists studied the effect of long-term cycling of the ketogenic diet (one week on, one week off the diet) compared to a normal diet in mice. Cyclical keto dieting reduced mid-life mortality and increased health-span.11
Measuring Ketone Levels
An essential, objective way to see if you’re in ketosis is to measure. There are three main ways to test for ketones—in the blood, in the breath and in the urine—each with its own benefits and considerations. The most accurate? Measure levels of BHB in the blood.
Macronutrient Composition for Keto Diet Success
A balanced macronutrient intake is essential for success on the keto diet. Macronutrients are food groups humans consume in large quantities. They provide the bulk of the energy to the body.
The primary macronutrients are carbohydrates, fats, and proteins.
The macronutrient composition of a diet can be described using the mass of each macronutrient, the ratio of macronutrients in the diet, or the percentage of each macronutrient in the diet. The variety of descriptions can make things a little confusing.
- A ketogenic diet contains about 5% of energy as carbohydrates.
- A ketogenic diet has a ratio of 2g – 4g of fat to every 1g of carbohydrates plus proteins.
- A classical ketogenic diet contains 20g – 30g of carbohydrate per day
Here are some examples macronutrients based on foods you might eat every day. Carbohydrates: bread, pasta, potatoes, cereals, sugary food (sweets). Fat: oils (olive oil, coconut oil), butter, fatty cuts of meat, brazil nuts, macadamia nuts, avocado. Protein: beef, chicken, pork, fish, milk, cheese, yogurt, eggs.
The main function of dietary carbohydrates is to be a source of energy. Some say that dietary carbohydrates are not essential, as they can be made from dietary protein and fat.12
Carbohydrates are biological molecules that contain carbon, hydrogen, and oxygen, usually with a 2:1 ratio of hydrogen:oxygen. Carbohydrates occur as a collection of single units (monosaccharides, e.g. glucose), two molecules joined (disaccharides, e.g. sucrose), and chains of molecules (oligosaccharides and polysaccharides).
When following a ketogenic diet, carb intake should be very low.
This contrasts with the modern western diet (how many Americans eat), which is high-carb: most dietary calories come from carbohydrates (and often, processed foods). Consuming carbohydrates causes insulin release (leading to higher insulin levels), which inhibits ketone production in the liver and thus ketosis. Therefore, monitoring and modulating your carbohydrate intake is an important part of following the ketogenic diet.
Dietary carbohydrates replenish the stores in muscle and liver (glycogen). They also maintain blood glucose concentrations to provide fuel for the whole body—but most importantly for the brain. Blood glucose is easy to measure using a handheld blood glucose monitor. Normal blood glucose levels fluctuate throughout the day and vary between individuals.
Ranges of Blood Glucose levels for clinical diagnosis are as follows:13
- Fasting: healthy = 4mM – 6 mM / 70mgDl – 110 mgDl
- Fasting: diabetic = ~ 7 mM / 125 mgDl
- 90 minutes post-meal: healthy = < 8 mM / 140 mgDl
- 90 minutes post-meal: diabetics = > 11 mM/ 200 mgDl
When you’re following the ketogenic diet, key concepts are the total amount of carbohydrates, the net amount of carbohydrates (accounting for the accompanying fiber), and the speed with which carbohydrates raise blood glucose (glycemic index). With a standard ketogenic diet, it’s recommended to keep the total amount of carbohydrates limited to less than 5% of energy intake.14
Dietary fiber is carbohydrate-based material from plants that is not entirely broken down by the small intestine. Instead, it passes to the large intestine, and either undergoes fermentation (which supports the growth of beneficial bacteria),15 or excretion. Fiber is a significant part of a well-formulated ketogenic diet. It helps to maintain gut health, and also increases food bulk and helps with the feeling of fullness. Green and cruciferous vegetables are rich in fiber and are helpful to include in a ketogenic diet.
Depending on how complex the source of fiber is, it has different assumed caloric values. One approach is to treat fiber as having the same amount of calories per gram as carbohydrates: 4 kCal/gram. However, as a proportion of fiber is not digested, other approaches use a lower value of 2 kCal/g. Digestion-resistant fiber does not contribute to calorie intake, as it is not broken down.
Net carbs refer to the mass of total carbohydrates, minus the total fiber, which could be a better metric to judge carbohydrate intake because:
- Fiber is mostly digestion-resistant and so should not increase blood glucose.15
- Studies have shown an increase in fiber does not affect blood ketone levels.16
The ‘glycemic index’ is a scale that ranges between 1 and 100, and it indicates how quickly food raises blood glucose after consumption. Pure glucose is the reference and is set at 100 (meaning, raises blood glucose quickly). Other foods have a comparatively lower value as they raise blood glucose more slowly. Example values for the glycemic index of food are white potato (~80), white bread (~75), apple (~35) and peanuts (~15).
Glycemic load accounts for both the speed of carbohydrate release and the total amount of carbohydrates in food. Food can have a relatively high glycemic index (i.e. carrot = 47) but because the total carbohydrate amount is low (carrot = 5g per serving), the glycemic load of one serving is very low.
Proteins are large molecules composed of chains of amino acids. The functions of dietary protein are:
- Building structural and functional components of cells
- Conversion to glucose via gluconeogenesis
- Top up intermediates in other metabolic pathways, such as the Krebs Cycle
While it’s possible for a protein to be used as a fuel, this isn’t its primary function.
When following a ketogenic diet, there must be a balance of sufficient protein to maintain muscle mass. If dietary protein exceeds 20% – 25% of calories, gluconeogenesis from protein can stop ketone production. Initially, target a protein intake of 0.8g – 1.2g per kilogram of body weight. This target balances the need for protein against the chance of excess gluconeogenesis.3
Some individuals (such as strength or endurance athletes) may have higher protein requirements. They might require a modified ketogenic macronutrient ratio of 2:1 fat: non-fat (where 65% of energy is fat, 30% is protein, and 5% carbohydrate) and can still be effective for therapeutic ketosis.
Fat gets a bad rap. In nutrition, fat is the dietary macronutrient made up of triglyceride molecules. The main functions of fats in the diet are to provide increased energy levels and makeup key functional and structural parts of the human system.
But we often misuse the word “fat.” There’s a difference between fat in cells and different types of fat molecules:
- Adipose tissue: the tissue that stores energy as fats/lipid droplets inside adipocytes (fat cells). This is body fat.
- Adipocytes: individual cells that store fats/lipids
- Lipids: the most general term forinsoluble and polar biological fat molecules. The lipid class of molecules includes mono-, di- and triglycerols, cholesterols, and phospholipids
- Triglycerides: a lipid molecule made up of glycerol (that acts as a backbone) joined to three fatty acid molecules
- Fatty acids: a molecule composed of a chain of carbon atoms bonded to one another with a carboxylic acid at one end
To be specific, our diet includes many sources of lipids.
Lipids are digested and travel in the blood as triglycerides and fatty acids before being used as a fuel, or stored by adipocytes in adipose tissue. Dietary lipids undergo many tightly regulated metabolic steps before storage in adipose tissue. Dietary fat does not equal stored body fat.
Triglycerides are the most important source of energy in a ketogenic diet. They account for > 70% of dietary calories. For those following a ketogenic diet, it’s helpful to understand how the lipid source in the diet is processed in the body.
Fatty acids can be saturated (no double bonds between carbons), or unsaturated (one or more double bonds between carbons).
Saturated fats are relatively stable and tend to be solid at room temperature (i.e. lard, butter, coconut oil). Historical guidelines recommended limited the intake of dietary saturated fats because fat consumption was thought to be associated with heart disease and high blood pressure. However, emerging research has shown saturated fat can have beneficial effects on blood biomarkers (i.e. increase healthy HDL cholesterol levels).17
Unsaturated fatty acids can be further divided into monounsaturated fats (only one double bond between carbons) and polyunsaturated fats (multiple double bonds between carbons). The number of double bonds is important as it determines how the fatty acid behaves both inside and outside of the body.
They tend to be liquid at room temperature (i.e. vegetable-based fats such as olive oil). Unsaturated fats are thought of as healthier than saturated fats (also known as “healthy fats”). Increased consumption of mono- and polyunsaturated fats have been linked to improved blood biomarkers (i.e. lower blood triglycerides).18 Eating enough unsaturated fats is important when following a ketogenic diet.
Increased fat consumption is not associated with cardiovascular disease.19
Eating a moderate amount of saturated fat is unlikely to be as harmful as previously believed, and saturated fat consumption as part of a ketogenic diet is unlikely to increase the risk of cardiovascular disease.
Trans-fats are produced artificially when hydrogen is added to unsaturated fatty acids in order to solidify it and make it last longer. Because of associations with poor health outcomes, these artificial fats had their generally regarded as safe (GRAS) status removed in 2015 by the FDA. 20 Avoid high levels of trans-fat consumption by eating a diet based around whole foods.
Essential fatty acids are important to include in the diet because the body cannot naturally produce them. This group includes poly-unsaturated omega 3, omega 6, and omega 9 fatty acids.
It’s believed the anti-inflammatory effects of essential fatty acids may have broad benefits for health and performance. Oily fish, such as sardines and mackerel, and seeds (i.e. flax) are good dietary sources of essential fatty acids.
The number of carbons in the fatty acid chain also has an important effect on its metabolism. The carbon chain of fatty acids can be up to 28 carbons atoms long. If there are > 13 carbons in the fatty acid, it is called a long-chain fatty acid, between 8-12 is a medium-chain fatty acid, and under 5 carbons is a short-chain fatty acid.
The body metabolizes fats differently according to chain length. Long-chain fatty acids are absorbed and go from the gut into the lymphatic drainage system and from there are released directly into the blood.
By comparison, medium- and short-chain fatty acids do not go into the lymphatic system. They travel in the blood from the gut directly to the liver.21 If a large amount of these short- and medium-chain fats are delivered to the liver at once, this can trigger the liver to convert them into ketones, even without dietary carbohydrate restriction.
Medium-chain fatty acids are highly ketogenic. They can be found in natural sources such as coconut oil or in an artificially purified form. However, for many people, consuming a high amount of medium-chain fatty acids can cause an upset stomach. This limits their use to raise ketones artificially.
When integrating these concepts into a ketogenic diet: target the majority of dietary calories as fat. Aim to include a variety of fats from different sources (grass-fed red meat in moderation, olive oil, coconut oil, nuts, and avocados).
Micronutrients on a Keto Diet
Conversely to macronutrients, micronutrients must be obtained in the diet in small quantities, but are essential to health. Vitamins and minerals are examples of micronutrients.
When following a ketogenic diet, it is important to be mindful of micronutrient intake because:
- Reducing carbohydrate intake can lower consumption of micronutrient-rich foods (i.e. fruits and vegetables)
- In the initial 28 days of following a ketogenic diet, the balance of some micronutrients (such as sodium, potassium, magnesium, and calcium) can become disturbed due to an increase in their excretion.22 The body resolves this issue naturally after adapting to the diet
Sodium is the principal cation in extracellular fluid. Its functions are related to blood volume maintenance, water balance, and cell membrane potential. Sodium is also essential for acid-base balance and nerve conduction.
The level of sodium can fall at the start of a ketogenic diet.
Adding extra sodium to meals (like adding salt or consuming bouillon/ bone broth) can reduce the chances of feeling the common side effects associated with low sodium (like cramps).
Potassium is the principal cation in the intracellular fluid. Its primary functions are related to maintaining cell membrane potential and electrical activity in cells such as neurons and cardiomyocytes. As with sodium, levels of potassium fall at the initiation of a ketogenic diet due to increased excretion. When starting a ketogenic diet, include sources of potassium like nuts, dark green vegetables, and avocados.
Magnesium is an essential element in biological systems, especially for nerve, muscle, and immune function. Levels of magnesium also fall at the initiation of a ketogenic diet due to increased excretion. When starting a ketogenic diet, include sources of magnesium like oily fish, dark green vegetables, and seeds.
Calcium has a role in muscle contraction and is important for cardiovascular and bone health. Calcium deficiency is less common during a ketogenic diet, as staples of the diet such as fish, cheese, and leafy greens are rich sources of the mineral.
Considerations When Starting a Keto Diet
As with any new diet or way of life, it’s important to look at the lifestyle change from all angles.
Who Should Avoid a Keto Diet?
Based on certain risk factors, following a ketogenic diet may not be suggested for people with the following medical considerations:
- Kidney failure
- Impaired liver function
- Impaired fat digestion (gallbladder disease, gastric bypass, pancreatitis)
- Genetic defects in metabolism (CPTI/II deficiency, beta-oxidation defects, fatty acyl dehydrogenase deficiency).
Potential Side Effects
When starting a ketogenic diet there can be a period of 2 – 3 days where blood glucose levels are low, but ketone production has not reached a sufficient rate to provide enough fuel for the brain.
- Muscle cramps
It can be initially tricky to adjust food intake to ensure adequate nutrition when following a ketogenic diet. Also, some people find the diet isn’t sustainable due to individual differences in metabolic state or lifestyle. If the diet does not provide the correct balance of macro and micronutrients, some individuals develop other symptoms beyond the keto flu after the adaptation period. These include:
- Bad breath
- Difficulty in maintaining physical performance
- Hair loss
- Elevated blood triglycerides or cholesterol
To treat these symptoms, ensure the diet provides enough calories and micronutrients. Many people reduce fruit and vegetable consumption on a ketogenic diet (due to carbohydrate content). This means it is easy to become deficient in vitamins and to under-consume fiber.
The ketogenic diet can alter the way that the kidneys excrete electrolytes (such as sodium), so electrolyte supplementation can reduce the side effects of an electrolyte imbalance. A silver lining here is the loss of excess water weight (and thus weight loss) with the decrease in stored water.
Possible Clinical Applications for Ketosis
Some of the earliest reports of the ketogenic diet describe its use in a clinical setting.
In the early 20th century, ketogenic diets helped treat drug-resistant epilepsy. Doctors also prescribed ketogenic diets to treat type 1 diabetes (different than type 2 diabetes, in which people have insulin resistance or don’t respond to insulin) before the invention of insulin.
As analytical techniques progressed, scientists learned that ketones themselves might be a crucial part of the success of the ketogenic diet to treat disease. From this finding stemmed a field of research to examine the potential benefits of ketosis in a range of disease states:
- Weight loss
- Diabetes and metabolic syndrome
- Neurological disease: epilepsy, Alzheimer’s disease, Parkinson’s disease, migraine, concussive disease, and traumatic brain injury
- Inflammatory diseases
While the ketogenic diet is not yet a first-line treatment recommended by doctors for any of these diseases, it’s a relatively easy and tolerable step that patients with these conditions can take to improve their health. Emerging research suggests there may be beneficial effects of ketosis for some people, and further studies are required to confirm how best to use the diet in these clinical settings.
Should You Start a Keto Diet?
We’ve provided an in-depth look at the keto diet, hopefully giving you all the tools you need to make the best decision for your health. Think about your goals, your lifestyle and how feasible keto is for you (and consult a healthcare professional). While many people have found success on keto for weight loss or performance—everyone is different.
(PLEASE SEE ORIGINAL ARTICLE FOR ALL 23 SCIENTIFIC CITATIONS, AS WELL AS IMAGES, GRAPHS, DIAGRAMS, ETC.)