Published on Apr 11, 2019. 14 minute read.

The modern human diet consists primarily of carbohydrate based foods (carbs) such as; potatoes, rice, fruits, grains, vegetables and dairy. In other words, over 60% of the calories we consume daily are in the form of simple sugars (glucose and fructose), starch and fibre (soluble and insoluble). The overconsumption of sugar has lead to a global obesity epidemic, which in turn has lead to a dramatic increase in serious chronic diseases like coronary heart disease, type 2 diabetes and bone and joint disease. According to the British National Health Service (NHS), obesity also contributes to life threatening diseases, such as cancer and strokes.

The Ketogenic diet, known simply as ‘keto’, is the process of re-training your body to use fat for energy, instead of carbs. As carbs are not an essential macronutrient, unlike protein and fat, we do not need to eat them as a species to survive or thrive.

Our bodies have a built in fallback process, called ketogenesis, which can produce all the energy we need to live from fat, whether that be ingested fat or fat stored within the body.

When you eat carbs, your body converts the sugars into glucose, which enters the bloodstream and eventually reaches the mitochondria (and ultimately provides energy to your cells). When there are few carbs available (less than 20g net carbs per day) the body will have no choice but to produce energy using alternative means, meaning from fat, using either fat eaten or fat already stored on your body.

After an initial induction phase of between 1 to 6 weeks, your body will adapt to using fat for energy. More precisely, a chemical process will take place in the liver and ketones will be produced. The act of triggering ketosis through diet is known as nutritional ketosis.

You can eat lots of healthy vegetables on the ketogenic diet

For most people, nutritional ketosis is achieved by consuming food with an overall macronutrient split of at least 75% fat, 20% protein and 5% carbs. If too many carbs are consumed in a day, the body will switch back to using them for energy and you have to start over. This is because carbs have a simple structure at the molecular level, and are easier to break down and utilize than fat. Your body prefers to store fat for use later, when times are hard and food is scarce. In the modern world, food is abundant all year round, so our bodies never have the need to access energy in reserve, so the supply only continues to grow over time.

Using carbs for energy is arguably the bodies preferred means of producing energy, but throughout human evolution has been a secondary process to fat burning. Earlier humans would have only had limited access to fruit and high starch vegetables (typically in the autumn) and would have spent the majority of the year hunting and eating animals, which are naturally almost carb free.

Keto is not the bacon and eggs diet. Keto is not the Atkins diet. You could eat all the processed meat and eggs you desire, but keto is more than that. Keto has a strong emphasis on eating healthier, more natural sources of fat (from avocado, nuts, etc) and promotes the consumption of leafy green salads and vegetables too.

We think of keto as the Atkins diet version 2.0.

What is ketogenesis

Without diving too deeply into the science (for now), ketogenesis is the general term used to refer to the process that occurs in the liver of breaking down fatty acids and amino acids to produce ketone bodies.

Ketone bodies are 3 water soluble molecules; acetoacetate, beta-hydroxybutyrate and acetone.

Ketone bodies are combined chemically and oxidized (combined with oxygen) and used by cells for energy. Ketones are fuel for cells, working similarly to how glucose works when eating a high carb diet.

Ketones are a healthy, natural, alternative power source your body can use for energy.

Who should try Keto?

Most people wanting to try keto do so for at least 1 of the following 3 reasons;

Person 1: Type 2 diabetes

This person is overweight or obese and has either developed type 2 diabetes or has been warned by their doctor or healthcare professional that they are on the path to doing so.

People in this category have been advised to eat a low carb diet, or have friends, family or a significant other who has made the recommendation, perhaps because they have tried the diet for themselves and seen positive results.

Type 2 diabetes suffers can control or reverse the condition altogether

Overweight or obese people, especially those with, or at risk of, type 2 diabetes, often see the best results. They lose weight faster (after all they have plenty of energy in reserve just waiting to be unlocked) and often see improvements in their overall health. Often they reduce or eliminiate the need altogether for insulin injections and/or other prescribed medication.

Keto is ideal for this person.

Person 2: Average weight person wanting a cleaner more natural diet

This person is not necessarily overweight, they might be lean, slim, or maybe skinny-fat. Typically this person do not have any particular health impedance or strong health concerns, but they want to break free of the standard western diet, significantly reduce their sugar intake, be free of constant hunger, and generally be well.

This person has probably heard that eating a diet higher in healthy fats and lower in sugar can help in all areas of their life, including (but not limited to); better cardiovascular health, reduced chance of developing neurological disorders like Alzheimer’s and Parkinson’s disease, and reduced chance of developing potentially fatal diseases like cancer and strokes. They also want healthier teeth and gums, improved mental clarity, better ability to concentrate, and, most importantly, they want to teach a healthier way of living to their children.

Keto is ideal for this person.

Person 3: Athletes looking to raise their game

This person wants to; develop and enhance muscular strength, and improve the aesthetics of their body by getting leaner and removing stubborn fat (especially around the midsection). They have tried traditional bodybuilding diets that consist of large amounts of carbs and protein, whilst steering clear from fats. They have had a mixed success with this type of diet and are looking for an alternative approach.

Keto is ideal for this person.

Who should not try Keto

There are not many types of people who would not see some benefits from trying keto. However, here are a few things to check/consider before starting;


Ketosis and diabetic ketoacidosis (DKA) are often misunderstood in the medical world, as medical professionals often confuse ketosis and ketoacidosis and believe that having high levels of ketones in the blood leads to ketoacidosis.

Diabetic ketoacidosis (DKA) is a very serious medical condition where there is a high concentration of ketones AND high blood sugar levels. The body runs out of insulin, which removes the sugar from the blood, and can ultimately result in death.

A person who is inducing ketosis through nutrition (nutritional ketosis) consumes significantly less sugar than typical (usually 20g a day or less) and will usually find a drastic reduction and stabilization in blood sugar levels as a result.

Having high levels of BOTH ketones AND high levels of blood sugar is certainly very dangerous and would require immediate medical attention. People on a ketogenic diet typically never encounter this, no matter how high the levels of blood ketones rise because of the stability of blood sugar levels.

If unsure, seek medical advice before trying keto.

Those with no willpower

If you have no willpower, this might not be for you.

When you actively start trying to avoid carbs, you will startlingly quickly come to realise that carbs are everywhere, and we mean everywhere. They are in your Starbucks coffee, your Subway sandwich, your morning doughnut, and even your cough syrup.

Yoghurt contains carbs, french fries contains carbs, ketchup contains carbs, and even your healthy sugar free cookies contain carbs. We hate to break it to you, but you will be hard pressed to find any normal food that people consume regularly that does not contain carbs.

What is worse is that when you stop eating carbs, your friends, family, acquaintances, and even your barista will try to convince you that you need carbs to survive and that you are the wrong side of crazy for wanting to avoid them.

If you are thinking to yourself that you “just will not tell anybody about the changes you are making to your diet”, think again. People will notice you skipping your morning slice of toast, your croissant at lunch, your pizza on a Tuesday night (Domino’s we are looking at you!), and that beer you usually go for on a Friday evening after work with colleagues. If, somehow, you dodge all that, people will notice your weight loss and start to ask questions about how you are doing it, eventually people will find out.

You need willpower, and a lot of it. If you have no willpower, then you probably will not be able to survive this way of eating. Just think of your long term health, and trust us, eating this way gets a lot easier over time.

Sugar may be more addictive than cocaine, and your a life long user. You need willpower to break the addiction. (Study).

Keto flu

It is quite possible that you have not experienced even mild levels of ketosis since you were a baby, assuming that you were breastfed by your mother. Newborn babies consume breast milk almost exclusively, and breast milk is high in fat, moderate in carbs and fairly low in protein. Breast milk can cause the child to enter a mild form of ketosis. Most babies enter a state of ketosis within a day or two of being born and will remain in this state until food is introduced or they are moved to a milk-substitute.

Formula milk is higher in carbs, which may result in the child not entering ketosis.

Either way, it is unlikely that you have experienced ketosis since you were a baby, or at least since a very young age. In fact, foods recommended for babies less than 1 year old include; cereal, sweet potato, meat, yogurt and Cheerios (seriously!). None of these foods are renowned for being low carb.

What does this mean to me? What we are trying to say is that it has been a very long time since your body has been geared up for fat burning, and there are some vital processes in the body that need to be active to make this happen. Further information on the science of the keto flu can be found here.


The keto flu is not the flu in the traditional sense (the keto flu is not a respiratory illness caused by the influenza virus). The keto flu varies from person to person but typical symptoms include (not limited to);

  • Tiredness, especially when exercising, even if you exercised regularly before
  • Headaches (take paracetamol if required)
  • Dizziness (more common)
  • Nausea (less common)
  • Inability to concentrate for periods of time
  • The desire to eat sugar (this is more mental than physiological)
  • Broken sleep and irritability
  • Bad breath, (not for the first couple of weeks until your body starts producing ketones, chew sugar free gum to reduce this)
  • Muscle cramps (caused by electrolyte deficiency)

See Ketovangelist and Ketosummit for more information on how to fix the above common problems.

For the first few weeks you may lose a significant amount of retained water. Carbs signal to the body to store water, so when you stop eating carbs this excess water drops off. In fact the first couple of weeks you are on keto, you will probably experience rapid weight loss; 3-6 lbs at least. Don’t be fooled you have not started losing weight yet, just water.

After about 1-2 weeks (everybody is different) your body will start producing an enzyme which kick starts ketogenesis and your body will gradually start returning to normal.

During the first couple of weeks it is important to stay well hydrated, take multivitamins and other supplements including; potassium, sodium (salt) and magnesium.

How to determine if you are in ketosis, or not

There are several options available to you should you want to test your ketone levels, with varying degrees of accuracy and financial cost.

Should you even bother testing ketone levels at all

The short answer is, probably, yes, especially when starting out. There are some obvious signs as to whether you are in ketosis or not. If you are experiencing increased energy levels, reduced brain fog, better concentration, less tiredness, bad breath, and reduced/non-existent hunger, then you are almost certainly in ketosis and you should probably not bother testing at all.

If you are not experiencing these benefits, and instead suffering from keto-flu like symptoms, then you are probably not in ketosis and may need to adjust your macronutrients (the solution to this is almost always to eat more fat!).

Blood testing

We recommend using a blood testing meter, like this one from GlucoRx (this is what we use), to most accurately test your ketone levels.

  • Light nutritional ketosis is considered to be between 0.5-1.5 mmol/L (millimolar per litre) of ketones.
  • Optimal fat burning ketosis is considered to be between 1.5-3.0 mmol/L of ketones.
  • More than 3 mmol/L is considered high, but only dangerous when combined with high blood sugar levels (which, on keto, you almost certainly do not have).

The highest level we have ever seen for ourselves is 5.6 mmol/L, and this was after prolonged fasting combined with intensive exercise. We confirmed we were not in danger of ketoacidosis (discussed in more detail in a subsequent post) by also performing a blood glucose test.

Conducting regular ketone level tests is an effective way to determine your carb sensitivity, which is different for everybody (and depends on the amount of metabolic damage you have incurred).

Carb sensitivity is also known as your carb threshold, the amount of carbs you can consume in a day and stay in ketosis. When performing regular tests, you can eat more or less of particular foods and observe the results.

Blood testing, however, can be expensive.

Urine test strips

Urine ketone test strips, like Ketostix are easy to get hold of and are relatively inexpensive compared to blood testing. They are never accurate and they stop working altogether after a few weeks. Ketones are only present in the urine in the early stages of becoming keto-adapted because your body is not efficiently using ketones produced through ketogenesis.

Urine test are helpful when you are starting out to tell you if you are in ketosis or not, but never reliably tell you the actual level of ketosis achieved.

Use with caution and throw away once you become keto adapted.

Breath tests

We have never tried keto breath tests, like this one from Ketonix, but our understanding is that they can be just as reliable as blood testing, without the need to draw blood.

Breath tests are where you breath in to a tube and the levels of acotate are measured.

Breath tests are not as readily available as blood tests.

Ketogenic kids

We are often asked if children can eat Keto. The simple answer is yes.

All the above statements are true for children and adults. In fact, since we introduced our child to keto his behaviour, concentration, and general attitude to his work has substantially improved. We have not got a lot of scientific studies to back up our claims, only anecdotal evidence from our own experiences.

Remember, children will experience the same keto flu-like withdrawal symptoms as adults, so be extra vigilant and adjust their calorie and macronutrient intake as required, the same way you would for yourself. Children are usually very active, compared to adults, and may require more water and salt than before.

Clever Kids
Clever Kids
The ketogenic diet can help children concentrate better at school

We have found that the pressure on children to eat sugar is just as great if not greater than for adults. Children are subjected to corporate advertising, peer pressure and expectations from family and other persons significantly involved in their daily lives (teachers, caregivers etc) to behave in a normal way. Refusing sugary sweets and snacks, whilst undoubtedly beneficial for their health regardless of whether they are “doing keto” or not, will raise eyebrows and will result in questions being asked.

We have found that educating our child about the benefits of a ketogenic diet has helped him make informed choices and answer questions as needed without fear of repercussions.

The ketogenic commitment, part time keto does not work

Keto cannot realistically be done on a part time basis. Once you get into ketosis, eating too many carbs will knock you back out again. We have found that it takes anywhere from 48-96 hours to get back into ketosis even at a mild level.

Regularly cycling in and out of ketosis is possible, as long as there is a long enough gap in between. Possible but not recommended.

We have experimented with carb cycling in the past, with little success. Keto is a longer term way of life and we try to stay keto adapted as much as possible. However, do not beat yourself up. If you have a cheat day and switch to a sugar burner, do not fret, make the most of it and get back to it as soon as possible.

We will discuss cheat days in a follow up post at a later date.


The ketogenic diet, keto, is a natural and healthy means of converting fat to fuel, and is induced through diet and nutrition. After an initial adaptation period, called keto-flu, you can start to utilize fat stored within your body to lose weight, get healthier, and achieve your fitness goals. Keto can reduce or eliminate the effects of type 2 diabetes, reverse obesity, and help control or prevent life threatening diseases. Keto is suitable for the whole family and can help children improve their behaviour and concentration at school. Keto is a lifestyle change, rather than a diet, and requires investment of time and energy to work correctly.


Jon Preece

About the author

Jon Preece is a professional front-end development specialist.

For over a decade, Jon has worked for some of the biggest and best UK based companies, on a wide range of products. Get in touch via Twitter.