What Is Ketosis?
Ketosis is a natural state for the body, when it is almost completely fueled by fat. This is normal during fasting, or when on a strict low-carb diet, also called a keto diet.
Ketosis has many potential benefits, but there are also side effects. In type 1 diabetes and certain other rare situations excessive ketosis can even become dangerous.
On this page you can learn all about how to harness the benefits of ketosis, while avoiding any problems. It all starts with understanding what ketosis is.
Choose a section, or keep reading below for all of them.
The “keto” in the word ketosis comes from the fact that it makes the body produce small fuel molecules called “ketones”.1 This is an alternative fuel for the body, used when blood sugar (glucose) is in short supply.
Ketones are produced if you eat very few carbs (that are broken down into blood sugar) and only moderate amounts of protein (excess protein can be converted to blood sugar).
Ketones are produced in the liver, from fat. They are then consumed as fuel in the body, including by the brain. This is important as the brain is a hungry organ that consumes lots of energy every day,2 and it can’t run on fat directly. It can only run on glucose… or ketones.
Maximizing fat burning
On a ketogenic diet your entire body switches its fuel supply to run almost entirely on fat. Insulin levels become very low and fat burning increases dramatically. It becomes easy to access your fat stores to burn them off. This is obviously great if you’re trying to lose weight, and studies show that ketogenic diets lead to more weight loss.3 But there are also other less obvious benefits.
When the body produces ketones it’s said to be in ketosis. The fastest way to get there is by fasting – not eating anything – but obviously it’s not possible to fast forever.
A low-carb or “keto” diet, on the other hand, can be eaten indefinitely and also results in ketosis. It has many of the benefits of fasting – including weight loss – without having to fast.
Learn more about a ketogenic diet
Ketones are brain fuel
It’s a common misconception that the brain needs carbs. The truth is that the brain happily burns carbs when you eat them. But if you don’t eat too many carbs, the brain is happy to burn ketones instead.
Fortunately our bodies has evolved to be smarter than that. Normally we have fat stores that lasts so that we can survive for many weeks (if not months) without food. Ketosis is how the body makes sure that the brain can run on those fat stores too.
Bottom line: We do not need to eat any carbs at all. The brain can happily run on fat.
Many people even feel more energized and focused when the brain gets to run on ketones, made from fat. And it certainly speeds up fat loss, if you’re trying to lose weight.
The Benefits of Ketosis
There are many benefits of ketosis. By giving your body and brain an almost unlimited supply of energy, you can increase your mental and physical endurance. It also reduces hunger, facilitating effortless weight loss.
Furthermore, as getting into ketosis requires eating very few carbs, it can effectively reverse type 2 diabetes. Finally, ketosis has been used for a long time to control epilepsy – often even without drugs.
How to Get Into Ketosis
To get into ketosis you need low levels of the fat-storing hormone insulin. The most important way to do that is to eat a strict low-carb diet, also called a ketogenic diet.
On top of the necessary ketogenic diet there are many ways to increase ketosis further. The most powerful is adding intermittent fasting.
Symtoms & How to Know You’re In Ketosis
How do you know you’re in ketosis? It’s possible to measure it by testing urine, blood or breath samples. But there are also other telltale signs, that requires no testing:
- Dry mouth and increased thirst. Unless you drink enough and get enough electrolytes, like salt, you may feel a dry mouth. Try a cup of bouillon or two daily, plus as much water as you need.
- Increased urination – another ketone body, acetoacetate, can end up in the urine. This makes it possible to test for ketosis using urine strips. It also – at least when starting out – can result in having to go to the bathroom more often. This is the main cause of the increased thirst (above).
- Keto breath – this is due to a ketone body called acetone escaping via our breath.4 It can make a person’s breath smell “fruity”, or similar to nail polish remover. This smell can sometimes also be felt from sweat, when working out. It’s often temporary. Learn more
Other, less specific but more positive signs include:
- Reduced hunger – many people experience a marked reduction in hunger.5 This may possibly be caused by an increased ability of the body to be fueled by its fat stores. Many people feel great while eating just once or twice a day, automatically ending up doing a form of intermittent fasting. This saves both time and money, while also speeding up weight loss.
- Increased energy – perhaps after a few days of feeling tired (the “keto flu“) many people experience a clear increase in energy levels. This can also be experienced as clear thinking, a lack of “brain fog” or even as a sense of euphoria.
How Do You Measure Ketosis?
There are three ways to measure for ketones, which all come with pros and cons:
Side Effects, Fears & Potential Dangers
When starting a low-carb ketogenic diet and reaching ketosis it’s common to get some side effects during the first week. Possibilities include headache, lethargy, irritability, leg cramps, constipation and heart palpitations.
These side effects are usually relatively minor and transient, and most of them can be avoided by getting enough fluid and salt.
Ketosis vs. ketoacidosis
There are many misconceptions about ketosis. The most common is mixing it up with ketoacidosis – a rare and dangerous medical condition that mostly happen to people with type 1 diabetes if they don’t take insulin.6 Even some health care professionals tend to mix up these two situations somewhat, perhaps due to the similar names and a lack of knowledge about the distinct differences.
Ketosis and ketoacidosis are not the same thing.
Ketosis is a 100% natural state, under full control by the body. It can be caused by a low-carb diet or by a brief period of fasting.
Ketoacidosis is a severe malfunction of the body, with excessive and unregulated production of ketones. This leads to symptoms like nausea, vomiting and stomach pain followed by confusion and finally coma. It requires urgent medical treatment, as it can potentially be fatal.7
This graph shows the vast difference in amount of ketones in the blood between ketosis and ketoacidosis:
It’s like the difference between drinking a glass of water vs. drowning in an ocean. Both situations are about water – but they are not the same thing. Drinking a glass of water will not make you drown. Nor does ketosis result in ketoacidosis.
If you have a functioning pancreas that can produce insulin – i.e. you don’t have type 1 diabetes – it would be extremely hard or, most likely, impossible to get ketoacidosis even if you tried. That’s because high ketone levels result in release of insulin, that shuts down further ketone production. In other words, the body has a safety net that normally makes it impossible for healthy people to get ketoacidosis.8
How to Reach Optimal Ketosis
Getting into ketosis is not a black or white thing. It’s not like you’re either in ketosis, or out of ketosis. Instead, you can be in different degrees of ketosis, as this chart demonstrates.9 The numbers below refer to values when testing blood ketone levels.
- Below 0.5 mmol/L is not considered “ketosis”. Although a value of, say, 0.2 demonstrates that you’re getting close. At this level you’re still far away from maximum fat-burning.
- Between 0.5 – 1.5 mmol/L is light nutritional ketosis. You’ll be getting a good effect on your weight, but perhaps not optimal.
- Around 1.5 – 3 mmol/L is called optimal ketosis and is recommended for maximum mental and physical performance gains. It also maximizes fat burning, which can increase weight loss.
- Values of over 3 mmol/L aren’t necessary. That is, they will achieve neither better nor worse results than being at the 1.5 – 3 level. Higher values can also sometimes mean that you’re not getting enough food (“starvation ketosis”). For type 1 diabetics, it can be caused by a severe lack of insulin that requires urgent attention.10
- Values of over 8 – 10 mmol/L are usually impossible to get to just by eating a ketogenic diet. It means that something is wrong. The most common cause by far is type 1 diabetes with severe lack of insulin.11 Symptoms include feeling very sick with nausea, vomiting, abdominal pain and confusion. The end result can be a state called ketoacidosis, that may be fatal. Needless to say abnormally high ketones requires immediate medical care.
How to achieve ketosis
There are many things that increase your level of ketosis. Here they are, from most to least important:
- Restrict carbohydrates to 20 digestible grams per day or less – a strict low-carb diet. Fiber does not have to be restricted, it might even be beneficial.12
- Restrict protein to moderate levels. If possible stay at or below 1 gram of protein per day, per kg of body weight. So about 70 grams of protein per day if you weigh 70 kilos (154 pounds). It might be beneficial to lower protein intake even more, especially when overweight, and then aim for 1 gram of protein per kg of desired weight. The most common mistake that stops people from reaching optimal ketosis is too much protein.
- Eat enough fat to feel satisfied. This is the big difference between a ketogenic diet and starvation, that also results in ketosis. A ketogenic diet is sustainable, starvation is not.
- Avoid snacking when not hungry. Unnecessary snacking slows weight loss and reduces ketosis.
- If necessary add intermittent fasting, like 16:8. This is very effective at boosting ketone levels, as well as accelerating weight loss and type 2 diabetes reversal.
- Usually not necessary: Supplement MCT oil and/or Bulletproof coffee.
- Usually not necessary: Supplement exogenous ketones.13
Two stories about achieving long-term ketosis
- Experiment: Optimal ketosis for weight loss and increased performance
- Four weeks of strict LCHF and ketone monitoring
- Final report: Two months of strict LCHF and ketone monitoring
Here’s a great ten-minute presentation about self-tracking one year in nutritional ketosis:
Do I have to reach optimal ketosis to experience the benefits?
In short, no. Many of the benefits, such as weight loss, are experienced at lower levels of ketosis (at least above 0.5). There are indications that you might need to reach higher levels of ketosis for high-level physical performance.
A master class in ketosis
Here’s a great presentation by Professor Jeff Volek, about the benefits of adapting your body to run on fat and ketones for fuel:
Do you want to understand what it takes to successfully and enjoyably reach and maintain long-term ketosis? Then there’s no better teacher than Professor Stephen Phinney. Get inspired here:
You can also learn a lot about ketosis from one of the world’s foremost researchers on the topic, Dr. Dominic D’Agostino:
Feel free to leave a comment below.
There are three different ketones, or “ketone bodies” used as fuel by the body. They are:
Learn far more than you’ll ever need about ketones here:
The brain consumes about 20% of the body’s required energy every day, despite only representing 2% of the body’s mass.
A good bonus for weight loss, if you can get your hungry brain to burn fat for you, 24-7. ↩
This can sometimes be measured as early as during the first day on a ketogenic diet:
This has been clearly demonstrated in several scientific studies:
Learn more about how to safely and effectively do a low-carb diet if you have type 1 diabetes:
In the most common case – type 1 diabetes – the treatment mainly includes insulin infusion and fluids.
Ketoacidosis is potentially fatal, but provided adequate and timely medical treatment it fortunately has a more than 99% survival rate. ↩
There are a few situations besides type 1 diabetes that can – in rare and extreme cases – result in ketoacidosis. These include doing a strict keto diet or fasting while breastfeeding or on a new class of diabetes medications called SGLT-2 inhibitors (e.g. Farxiga, Jardiance, Invokana). ↩
The chart is from the excellent book The Art and Science of Low-Carbohydrate Performance by Professor Stephen Phinney and Jeff Volek. Highly recommended.
Take insulin, eat carbs (if your blood glucose isn’t already high), and contact medical services immediately. ↩
Fiber is digested by bacteria in the colon, and some of it is transformed into a fat called medium-chain triglycerides. This fat can be absorbed by the body and is very effective at turning into ketones. Thus eating more fiber (but still very low carb) could result in higher ketone levels in the blood. ↩
The company Prüvit sells drinkable ketones, called KETO//OS. This drink raises blood levels of ketones and may possibly improve physical and mental performance under certain circumstances.
However, it does not lower insulin or blood sugar, and it does not increase fat burning. Thus it hardly helps with weight loss or type 2 diabetes reversal.
Also note that they are selling through a multi-level marketing scheme, meaning their affiliates are paid on commission. So take all endorsements with a grain of salt.