This post covers the basics about ketogenic diets in detail for beginners and other curious people. I follow a ketogenic diet myself and use it in my clinical practice every day, so I've included information that comes from my own personal experience as well as from researchers and other seasoned clinicians. You'll also find a collection of print and on-line resources at the bottom of the page.
What is the ketogenic diet?
The ketogenic diet is a low-carbohydrate, adequate-protein, higher-fat diet that forces most of your cells to switch from burning mainly sugar (glucose) to burning mainly fat (fatty acids and ketones). This is why many keto advocates say that this way of eating "turns your body into a fat-burning machine." Ketogenic diets can be different from standard low-carbohydrate diets (such as Atkins and LCHF) because they typically limit protein to only the amount your body needs, whereas other low-carb diets typically allow you to eat as much protein as you want. It is called "ketogenic" because it allows your body to generate ketones that can be measured in the blood. By keeping carbohydrate intake extremely low and putting a cap on protein, you give your body no choice: it simply has to burn more fat for energy. This diet reliably lowers blood sugar and insulin levels, and controls appetite beautifully in most people.
Where does blood sugar come from on a ketogenic diet?
On a standard diet that includes plenty of sugar and starch, the body makes blood glucose primarily out of the carbohydrates you eat, but on a ketogenic diet, there isn't enough carbohydrate in the diet to allow that to happen. Luckily, the body can turn the fat and protein you eat into glucose using a natural process called "gluconeogenesis", which means "making glucose from scratch." On a ketogenic diet, you generate blood glucose from fat and protein, and this process reliably maintains healthy blood sugar levels. Most of your cells will choose to burn fatty acids or ketones instead of glucose if they can, so your body's total demand for glucose will be much lower than usual.
Doesn't the brain need glucose?
YES. Most cells in the body can safely switch from burning glucose to burning fatty acids or ketones, but there are important exceptions. The brain can use ketones to a large extent, but still must have access to some glucose at all times to meet its full energy demands. Even under optimal ketogenic diet conditions, about one-third of the brain's energy must still come from glucose for your brain to function properly.
Health benefits of the ketogenic diet
There are many good reasons to seriously consider trying a ketogenic diet. Burning fat is cleaner, safer, and more efficient for most cells than burning sugar (glucose). I believe Dr. Ron Rosedale puts it best:
The more fat that one burns as fuel, the healthier the person will be, and the more likely they will live a long time. The more sugar a person burns, the more disease ridden and the shorter a lifespan a person is likely to have.
Scientific research shows that ketogenic diets can be useful in managing a wide variety of difficult-to-treat medical conditions, including all of the below:
- Type 2 diabetes
- Epilepsy (seizure disorders)
- Heart disease
- Alzheimer's disease
- Bipolar disorder
- Headaches and migraines
- Polycystic ovarian syndrome (PCOS)
- Parkinson's disease
- Traumatic brain injury
- Multiple sclerosis
- Sleep disorders
- Amyotrophic lateral scoliosis (ALS or Lou Gehrig's disease)
That's a pretty impressive line-up.
Are ketogenic diets safe?
I wish more people would ask this question about the standard American diet. . . . Yes, ketogenic diets are safe for most people—much safer and healthier than the standard American diet, in fact, but there are important exceptions. Please read my short post "Is the Ketogenic Diet Safe for Everyone?" before you consider trying a ketogenic diet to see if you are in a higher-risk category. Please always consult with your health care provider before starting a ketogenic diet to be sure that it is appropriate for you. If you take medications, your prescriber will need to monitor your progress and be willing to make any necessary adjustments to your medications along the way, particularly during the early weeks of the diet. If you take psychiatric medications, please read my Psychology Today article Ketogenic Diets and Psychiatric Medications before embarking on a ketogenic diet.
What are ketones?
When your carbohydrate intake is very low and your protein intake is just right, your blood sugar and insulin will gradually fall to lower, healthier levels and become much more stable. Under these conditions, your body will start to break down fat and transform it into "ketones" that many cells can burn for energy instead of glucose (sugar). These ketones are released into the bloodstream and can be measured at home using a blood ketone meter. There are three types of ketones, but the one that our cells prefer to use is called beta-hydroxybutyrate:
- acetone can't be burned by cells for energy and comes out in your breath. This is the ketone measured by breath analyzers. Once fully adapted to a ketogenic diet (which can take at least 3 weeks) muscle cells can turn acetone into beta-hydroxybutyrate.
- acetoacetate is the ketone measured by urine ketone strips. Its metabolism is complicated. Urine acetoacetate levels may fall as you adapt to a ketogenic diet, so urine strips sometimes aren't as reliable over the long term. Acetoacetate can break down into either acetone or beta-hydroxybutyrate.
- beta-hydroxybutyrate is the most efficient fuel source for cells, and the primary ketone found in the blood when in ketosis. This is the ketone measured by blood ketone strips, the most reliable measurement method available in my experience.
Ideal blood ketone recommendations vary widely among experts, but generally speaking, if your blood ketone level falls between 0.5 mM and 5.0 mM, you are "in ketosis." Some clinicians recommend aiming for the higher end of this range if you are trying to treat a serious medical condition such as cancer, epilepsy, or schizophrenia, whereas people who are trying to lose excess body fat, normalize diabetic blood glucose levels, or treat other simpler conditions often find it sufficient to generate ketones between approximately 1.0 and 2.5 mM.
Macronutrient recommendations to achieve ketosis
The exact amount of carbohydrate, protein, and fat you should eat on a ketogenic diet in order to bring your ketones into ketosis range depends on many factors, including:
- Body composition (muscle and fat mass, lean body weight, height)
- Presence of illness or injury
- Activity level
- Metabolic health (how insulin resistant you are)
- Health goals
This is why I completely agree with the advice in the excellent book Keto Clarity, by Jimmy Moore and Dr. Eric Westman, that each person needs to experiment to find his/her personal carbohydrate and protein limits. However, general guidelines are provided below to give you ballpark estimates.
How much carbohydrate can you have on a ketogenic diet?
Carbohydrate tolerance varies from person to person. While it is perfectly safe to eat no carbohydrate at all, most people eating a ketogenic diet do eat small amounts of carbohydrate in the form of non-starchy vegetables and low-sugar fruits such as berries. In their indispensable book The Art and Science of Low-Carbohydrate Living, Drs. Phinney and Volek write that some people (typically athletes) can get away with up to 100 grams per day. However, most people need to go below 50 grams per day, and those with diabetes or significant insulin resistance typically need to stay below 25 grams per day.
I would add that it is best to spread carbohydrate intake out over the day rather than eat it all in one sitting. It is also best to avoid refined carbohydrates (sugar, syrups, flour, fruit juice, etc) to minimize risk of blood sugar spikes. I recommend you start with a maximum of 10 grams of carbohydrate three times per day and adjust up or down from there. Cancer nutrition expert Patricia Daly recommends that cancer patients keep carbohydrate to no more than 12 grams per day.
"Net" carbs = total carbohydrate grams minus fiber grams. Some clinicians recommend counting net carbs while other recommend counting total carbs. Again, this question is best answered using personal experimentation. To learn which types of carbohydrate and how many grams of carbohydrate you can personally tolerate, I highly recommend investing in a blood glucose meter and checking your blood glucose one hour after eating a meal that contains the carbohydrate you are interested in. If your blood glucose rises too much after eating (especially if it reaches 140 mg/dL or more), triggers cravings, or makes you feel foggy, depressed, tired or anxious, then it is likely you'll need to reduce the quantity or type of carbohydrate you're eating to maintain your blood glucose in a healthy range. Please read my post "The Number One Tool for Improving Your Health" to learn why I recommend testing blood glucose one hour after meals when you're first getting started. For those who can afford it, a continuous glucose monitor provides frequent glucose measurements (without fingersticks) that help you understand your personal responses to meals, snacks, and beverages.
Some people eat a so-called "carnivore" diet, which is a plant-free diet. This diet contains the least amount of carbohydrate possible and is sometimes also called a "zero-carb" or "ZC" diet. If you're curious to learn more about this option, please see my post The Carnivore Diet for Mental Health?
How much protein can you have on a ketogenic diet?
Recommendations vary widely, so use the suggested ranges below as a starting point and then adjust up or down until you find the amount that works best for your metabolism. In their book The New Atkins for a New You, Drs. Westman, Phinney and Volek provide a reference chart listing protein gram recommendations based on height and gender. According to their guidelines, as a 5' 5" woman, I should eat between 75 and 156 grams per day of protein. In his book The Rosedale Diet, Dr. Rosedale recommends I eat 77 grams of protein per day based on my body measurements, but 47 grams of protein per day based on my body fat percentage. When I plug my personal information into this wonderful free ketocalculator I am advised to start with 78 grams of protein per day.
So, as you can see, the recommendations for my situation are all over the map, varying from as low as 47 grams to as high as 156 grams of protein per day. What turned out to be true for me? I am a 5' 5" woman, age 55, who exercises regularly and has insulin resistance. In my case, when I follow a standard ketogenic diet that includes a few plant foods, I need to keep my daily protein intake between 60 and 80 grams per day in order to stay in ketosis. However, I was fascinated to discover that when I experimented with a carnivore diet, I was able to eat nearly twice as much protein and still remain in ketosis. This protein page applies to those following a standard keto diet, not to those following a carnivore diet.
I recommend you calculate your ideal body weight in pounds or kilograms using this free calculator, and then use the simple formulas below to calculate your starting protein grams.
- If you measure your weight in POUNDS: Ideal body weight in pounds X 0.45 = # protein grams per day. For example, if your ideal body weight is 135 pounds, multiply 135 by 0.45 to get 60.75 (or 61) grams of protein per day.
- If you measure your weight in KILOGRAMS: Ideal body weight in kilograms = # protein grams per day [you don't have to multiply by anything; # kilograms = # protein grams]. For example, if your ideal body weight is 70 kilograms, your starting number of protein grams will be 70 grams per day.
These are just ballpark estimates to get you started. You may need to eat less protein if you are very sedentary, or you may need to eat more protein if you are very active, for example. It would be unusual to need to raise these starting protein estimates by more than 50%. For example, if the above estimates suggest you should start with 70 grams per day, even if you are very active, it would be unlikely that you'd need to go higher than 70 X 1.5 = 105 grams per day.
NOTE: If you are pregnant, breastfeeding, or under 18 years of age, please consult a specialist for recommendations about your protein requirements.
Protein is a complicated and controversial topic with no clear consensus among experts. I recommend reading this excellent guide by registered dietitian Franziska Spritzler written for DietDoctor.com: Protein on a Low-Carb or Keto Diet.
[Keep in mind that grams of meat does not equal grams of protein, and that protein requirements vary significantly based on individual circumstances. For more information, please see my protein page.]
How many fat calories can you have on a ketogenic diet?
This is a controversial question. It is extremely important on ketogenic diets to eat fat, because both other macronutrients—carbohydrate and protein—are limited. If you don't eat enough fat, you could enter starvation mode (not good). But can you really eat as much fat as you want? Many people seem to be able to eat unlimited quantities of fat and still reach their health goals. In fact, some NEED to eat very high quantities of fat in order to achieve the high ketone levels needed to reach their goals. However, some people who are trying to use the ketogenic diet specifically for weight loss find that they need to be mindful not to overdo fat calories.
It makes sense when you think about it: yes, the ketogenic diet turns you into a fat-burning machine, but if you're trying to lose weight, you want your body to be burning some of your own body fat, not just the fat in the foods you're eating. Regardless, do not attempt a low-fat ketogenic diet. It is vitally important to eat healthy fats with every meal to ensure proper digestion, vitamin absorption, and enough calories to prevent your body from entering starvation mode, which will trigger stress hormones that fight against weight loss and endanger your health. I recommend using this easy, free ketocalculator to estimate your fat intake.
Do macronutrient ratios matter?
I like to focus less on percentages of fat, protein and carbohydrate and more on grams. This is because percentages can be misleading. Let's say your body responds well and remains happily in ketosis at 70 grams of protein and 25 grams of carbohydrate per day. If you follow percentage rules, the more calories you eat per day, the more protein and carbohydrate grams you can eat per day. I find it much easier and more logical to establish your daily protein and carbohydrate limits in grams, then eat the rest of your daily calories as fat. I don't generally count fat grams or calories myself; if I'm hungry I eat more fat and I don't worry about the totals. My calories and fat grams vary a lot from day to day, but my protein and carbohydrate stay about the same.
Preparing to start a ketogenic diet
- Again, please consult with your health care provider before taking the plunge. If you are hoping to use a ketogenic diet to treat a serious medical condition such as epilepsy or cancer, it is critical that you work with a specialist who can monitor your progress. If your practitioner won't support you in your efforts because he/she isn't familiar with ketogenic diets or believes ketogenic diets are unhealthy, you may want to consult with someone new. DietDoctor hosts an international list of low-carb doctors, LowCarbUSA maintains a list of low-carbohydrate providers on their website, and Marika Srobos has created a Low-carb Map of the World, that lists doctors, nutritionists, and other professional resources.
- If you are interested in using a low-carbohydrate diet of any kind to try to treat a mental health condition, please first read the comprehensive, fully referenced online guide I wrote for the DietDoctor website. It is published in four installments and is free to everyone (no membership required). I recommend this guide to your health care team as well, as it includes important information about the science and implementation of low-carbohydrate diets, as well as critical medication management advice.
- "Low Carb and Mental Health: The Food-Mood Connection"
- "How Sugar May Damage the Brain"
- "Low Carb and Mental Health: Getting Started and Managing Medications"
- "FAQ about Low-Carb Diets and Mental Health"
Important: if you take diuretic medication such as Lasix or Hydrochlorothiazide, or any blood pressure medications, your doctor will need to monitor your dosage closely during the first few weeks of starting a ketogenic diet.
If you take any psychiatric medication, please read my article "Ketogenic Diets and Psychiatric Medications" for safety information about drug interactions with a ketogenic diet. Please do NOT begin a ketogenic diet without working closely with your prescriber to make any necessary dosage adjustments along the way. I don't make this recommendation lightly—significant and even potentially dangerous medication side effects can occur.
Tips for ketogenic success
It is beyond the scope of this website to provide specific instruction about how to embark on a ketogenic diet, because we are each so unique in how we respond and in which adjustments we may need to make along the way. Instead, I'll provide general information that may be useful as you go forward.
Measuring blood glucose
When you're first starting out, it's a good idea to measure your blood glucose from time to time until you achieve good stability. Measuring before you've had anything to eat or drink in the morning (except water) gives you your fasting blood glucose, which should ideally fall somewhere between about 70 and about 85 mg/dL. Once you've adapted to a ketogenic diet, you may find your morning fasting glucose is a bit higher--sometimes even as high as 110 mg/dL. To understand why this occurs, please read this helpful article on DietDoctor about adaptive glucose sparing. If you are not achieving ketosis, continuing to experience cravings, or not making progress towards your health goals, it can also be very helpful to check blood glucose one hour after meals, as described above and in this post.
Important: If you take a diabetes medication or insulin to lower your blood sugar, your doctor will need to monitor and adjust your dosage during the first few weeks of starting a ketogenic diet.
Measuring blood ketones
I measure mine before my first meal of the day, but some experts prefer measuring later in the day, and some recommend measuring more than once a day. What's most important, if you ask me, is that you decide on a time of day you want to measure ketones and stick roughly to that same pattern every day when possible, so you can be comparing apples to apples when you're looking for trends.
Ideal ketone levels vary depending on your health goals and whom you ask. When your ketones rise to 0.5 mM, you are officially in mild ketosis. I personally aim for moderate ketosis and feel best when my ketones are between 1.0 mM and 2.5 mM. whereas some conditions, most notably seizure disorders and cancer, may require deeper ketosis with ketones of at least 3.0 mM.
Carbohydrate withdrawal happens
The first few days of any low-carbohydrate diet can be uncomfortable because your body goes through carbohydrate withdrawal: headaches, irritability, lightheadedness, cravings, difficulty concentrating, anxiety, insomnia, and even full-blown panic attacks can occur, but keep in mind that none of these are life-threatening and they often improve significantly within a few days in most cases. Some people prefer to begin with a standard low-carbohydrate high-fat diet for a week or two and then shift to a ketogenic diet by lowering protein into the desired range.
Practice, not perfection!
It can take time to figure out your personal carbohydrate and protein limits. If you aren't in ketosis by Day 5, you probably need to lower your carbohydrate or protein intake. If you do something human like overeat carbohydrate or protein when out with friends or on a special occasion or just because you were tempted, don't worry about it. Just get back on the horse the next day.
How long does it take to adapt to a ketogenic diet?
Keto-adaptation takes time and varies from person to person. Generating ketones can take as little as 2-3 days, but just because your ketone meter shows that you have plenty of ketones in your bloodstream doesn't mean your cells are good at burning them for energy right away. Some people have no trouble switching from a regular diet to a ketogenic diet, while others experience "keto-flu" symptoms such as lightheadedness, fatigue, headaches, constipation, depression, and difficulty concentrating in the beginning. On average, it takes 3 to 6 weeks for your cells to ramp up their internal systems to be able to make good use of the ketones you are producing.
Keto-adaptation, fluid balance, and electrolytes
During the first few days especially, as your insulin levels come down, your body will let go of excess fluid through urination. This natural diuretic effect is a very good thing, but can cause temporary electrolyte imbalances that can contribute to "keto flu" symptoms. This diuretic effect also tends to lower blood pressure, and can have a significant effect on the level of certain medications in the bloodstream.
You can minimize the potential for discomfort by staying hydrated and getting enough salt (sodium, potassium and magnesium). Some people take electrolyte supplements in the beginning to support their adaptation to ketosis. There are many good sugar-free electrolyte drink recipes available on the internet (Robb Wolf's LMNT is a good option), but the basic ingredients you'll need are potassium chloride (salt substitute—sold in grocery stores), sodium chloride (salt), and water. Recommendations vary, but aim for about 5 grams (5000 mg) of sodium and about 1000 mg of potassium, divided into two or three drinks per day. It is best not to add magnesium salts to your drink because they can cause diarrhea. Slow-Mag supplements are a better choice. Aim for about 300 mg of magnesium per day, preferably in the form of magnesium malate. Magnesium can also be absorbed through the skin, so bathing in epsom salts or using a magnesium skin spray or cream may help improve your magnesium levels without risking digestive side effects.
Potential side effects of the ketogenic diet
If you still don't feel well even after plenty of adjustment time (3 to 6 weeks) and using electrolyte supplementation if necessary, you will need to do some troubleshooting. A few of the more common issues ketogenic newcomers may have to sort out are listed below.
When switching to a ketogenic diet, most people make dramatic changes to the types of foods they eat. Coconut, nuts, dairy, fermented gourmet foods, avocado, seeds, non-starchy vegetables, and eggs are all very popular ketogenic foods because they are high in fat and/or low in carbohydrate, delicious, and filling. The problem is that many of these foods are common triggers for food sensitivities, so if you don't feel well on your new ketogenic diet, you may have an unrecognized issue with one or more of these keto-friendly foods.
Food sensitivities are not true allergies, so there are no laboratory tests to guide you. Before you give up and decide that a ketogenic diet is wrong for you, be sure to experiment with food elimination to make sure your symptoms aren't due to a food reaction. Food sensitivity can cause a staggering number of annoying and distressing symptoms, including headaches, constipation, bloating, fatigue, insomnia, dark circles under the eyes, stomach pain, skin changes, and body aches, just to name a few!
Contrary to popular belief, constipation is not caused by fiber deficiency. Please see my short post "Constipation and Ketogenic Diets" for simple suggestions about how to troubleshoot this common side effect.
If you have trouble sleeping beyond the early transition phase of the diet, this may be a sign that you are not eating enough calories, especially if you wake up hungry in the middle of the night. If your ketones are very high (above 4.0 mM), you may wish to increase your protein intake to see if that helps. If your ketones are moderate, try increasing your fat intake first. Another possibility is that you are eating more fermented foods than usual, which can cause symptoms of histamine intolerance, including insomnia for some people.
These are usually in the calves or feet and are often due to dehydration or electrolyte imbalances, so make sure to drink some water before bedtime and supplement with electrolytes as described above. The other possibility is unrecognized food sensitivities to something you are eating more of on your new diet. For more information please see my post "7 Tips for Restless Legs Syndrome."
Ladies, if your cycle is usually regular and your ketogenic diet causes delayed or missed periods, it is very likely you are not eating enough protein or fat. Missed or delayed periods are a sign that your body doesn't have enough calories to function properly, so increase your intake and see if that's the problem.
Not losing weight on your ketogenic diet?
The most common issues that can interfere with weight loss on ketogenic diets are:
- Eating too much carbohydrate, protein, or fat for your metabolism [in that order]. Please see the sections above on this topic for more details.
- Not eating enough calories. This will put your body into starvation mode, which triggers your stress hormones to fight against weight loss.
- Low-calorie or no-calorie sweeteners. Whether they are natural or artiificial, substances that taste sweet can raise your insulin levels and prevent your body from burning fat.
- Dairy products naturally contain hormones and other ingredients that stimulate human insulin and growth hormone systems, which can put your body into growth and storage mode rather than fat-burning mode. I know things like heavy cream and aged cheeses are favorites among the low-carb crowd, but they can stop weight loss dead in its tracks for some.
- Caffeine raises stress hormone levels, which can raise blood sugar and contribute to mild blood sugar and appetite instability.
- Eating too frequently. Try intermittent fasting by simply not snacking after dinner and waiting 14 to 18 hours before eating your first meal of the next day.
Difference between ketogenic diets and starvation
People eating a ketogenic diet are NOT in starvation mode because they are eating food. A ketogenic diet contains adequate protein and plenty of fat calories. You should not feel hungry or deprived once you've adapted to a ketogenic diet. If you do, you are either eating too much carbohydrate, which can trigger cravings and stimulate appetite, or you are not eating enough fat or protein to meet your body's needs, and should adjust your intake accordingly.
Difference between ketosis and ketoacidosis
Ketosis is NOT ketoacidosis. Ketoacidosis is a medical emergency caused by severe insulin deficiency. Without insulin, blood glucose and ketone acids rise to extremely high levels causing blood pH to fall into the dangerously acidic range. This occurs primarily in people with type I diabetes who have lost the ability to produce insulin. While it is true that insulin levels are much lower on a ketogenic diet than on a regular diet, it is virtually impossible for them to fall to the extremely low to zero levels seen in people with type I diabetes.
|Blood Levels||Normal Diet||Ketogenic Diet||Diabetic Ketoacidosis|
Is ketosis natural?
Ketosis naturally occurs in all humans when we haven't eaten for a while; this means ketosis can occur to a mild degree overnight while sleeping, depending on the length of time between dinner and breakfast. Babies are born in ketosis. Ketosis also naturally occurs during prolonged fasting and starvation to preserve precious glucose for parts of the body that can't switch completely to burning fat. Some people believe that our hunter-gatherer ancestors ate a ketogenic diet, but I doubt that most pre-agricultural peoples spent all of their time in ketosis, since they would have eaten whatever was available to their satisfaction as often as they were hungry. Depending on season and location, some of them may have been eating high amounts of carbohydrates from fruits and root vegetables. None of them were counting protein or carbohydrate grams, that's for sure. I view carefully formulated ketogenic diets as therapeutic diets that take advantage of a natural biochemical mechanism to treat the many metabolic diseases our modern lifestyle has inflicted upon us.
In addition to the books I referenced above, I highly recommend The Art and Science of Low-Carbohydrate Performance by Jeff Volek Phd RD and Stephen Phinney, MD PhD. This is THE book about ketogenic diets for athletes.
Nutritionist Maria Emmerich has written numerous fantastic ketogenic diet cookbooks. I strongly agree with her approach toward keto diets which minimizes sweeteners and processed foods (even the low-carb ones!) and emphasizes whole foods. I also appreciate that she clearly marks recipes containing common food sensitivity culprits (nuts, dairy, eggs, etc.) and offers substitutions when possible.
Recommended online resources
- "Ketosis Done Right: Meet Anne" Read the testimonial of a middle-aged woman who easily and successfully lost weight on a ketogenic diet.
- Patricia Daly is an Ireland-based nutritionist who writes expertly about ketogenic diets for the treatment of cancer.
- Ellen Davis is a nutrition writer who hosts a comprehensive website about all aspects of ketogenic diets.
- Dr. Ron Rosedale writes about ketogenic diets, health, metabolism and longevity on his website.
- Dr. Peter Attia writes about the biochemistry of nutritional ketosis.
- Amber O'Hearn writes about the science behind ketogenic diets for health.
- Matthew's Friends is a parent-run site about the use of ketogenic diets in children with epilepsy.
- The Charlie Foundation promotes the use of ketogenic diets in the treatment of children with epilepsy.
- Reddit hosts a ketogenic community.
Ketogenic diet for mental health resources
For a list of videos, podcasts, articles, and more, check out my post "Ketogenic Diets for Mental Health: A Guide to Resources."