April 19

An Evidence Based Look at The Ketogenic Diet


The ketogenic diet is an advanced nutrition protocol due to its complex nature and highly debated methodology.

Despite it looking ‘simple’ on the outside, as essentially it is a diet based solely around the manipulation of carbohydrates, when we understand how it works on a cellular level and investigate the finer details it can become quite advanced.

This has also left the ketogenic diet open to much controversy, and there is much debate about how such a restrictive diet can fit successfully into one’s lifestyle, and whether it is more effective in the process. 

This article will show you how it works, the benefits and negatives of this diet and how you can go about creating such a diet for clients.

This article is not exhaustive in relation to the level of information available on this diet but is a summary of the most important information surrounding it. It is recommended that you research further the references and further reading list at the end of this article before applying the information.

The information shared here is a shortened and condensed version of that reading list. 

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Potatoes are forbidden on the ketogenic diet

What is The Ketogenic Diet

As already mentioned, a ketogenic diet is based around the manipulation of carbohydrates in someone’s diet. 

The difference between this diet and others that restrict carbohydrates is the fact that it is trying to induce a series of adaptations within the body. 

In particular a traditional ketogenic diet is one that heavily restricts daily carbohydrate intake (typically 100g or less per day) which causes ketone bodies to be produced by the liver. The result is a shift in the body’s metabolism, as fat utilization becomes a priority over glucose.

Therefore, the goal of a ketogenic diet is to restrict the energy intake from carbohydrates in order for the body to run on fat for energy.

Ketogenic diets are not new, and some of the early research conducted on them stems back to the early 1900’s. The discovery of ketogenic diets and their benefits appeared to result from initial research based on fasting. 

Fasting (going without any food) was initially used by doctors trying to control patients with epilepsy. It was considered a successful way to control seizures, however refraining from food long term is not doable.

This led to further research as it was later discovered that a very low carbohydrate diet brought similar benefits as seen in those with epilepsy who fasted. This research then led to the release of the first ketogenic diet for the treatment of epilepsy in 1921 by Dr. Wilder.

Since then we have seen various waves of popularity for this dieting approach, but it is firstly considered to be a practical approach to controlling epilepsy seizures without the use of drugs throughout the medical world.

More recently we have seen the increasing use of ketogenic diets by those seeking changes in body composition. This stemmed from those who were experimenting with low carbohydrate diets for fat loss, however it was not known if this was purely due to a restriction in overall calories or not.

This was soon tested by Dr. Atkins who released his ketogenic diet known as the ‘Atkins diet’ which prescribed unlimited amounts of protein and fats, while still promising weight loss.

The effectiveness of this diet is now clear and since then we have continued to see multiple protocols based on a ketogenic or cyclical ketogenic diet matched to various populations and goals.

Ketogenic and cyclical ketogenic diets have also become popular with athletes and bodybuilders as they too constantly try to push the limits of body composition and health. 

How Does The Ketogenic Diet Work

The basic philosophy of the ketogenic diet is to create a metabolic response in the body, and the process by which this occurs can become quite detailed. 

The body uses the 4 following sources of fuel primarily: 

• Glucose (carbohydrates)
• Amino acids (protein)
• Free fatty acids (fats)
• Ketones

The first three are obtained by our diet, and in times of a calorie deficit the body can also seek out additional resources of these from various places within the body for energy.

Under these normal conditions ketones do not play a huge role in the energy demand, but during a ketogenic diet this all changes.

This basis of a ketogenic diet is to use ketones as the primary source of energy for the body, thus creating a metabolic shift from glucose. This why carbohydrates must be restricted (or limited) in order to make this happen.

This metabolic shift occurs when the body becomes depleted of glucose in its muscle and liver cells. The body can only store limited amounts of glucose, so it can only act as a short-term energy source. Once this occurs, the long- term energy source, fat, is called into play.

In summary, a tissue in the body will use the fuel source that has the greatest concentration in the blood stream.

When we reduce carbohydrates, glucose levels are reduced in the blood stream and fats will become the dominant fuel source due to higher concentration in the blood stream.

It should also be noted that this is not a permanent situation, so if carbohydrates levels are increased and become the primary factor in the blood stream, glucose is instantly used as the fuel source.

We also highlighted at the start that amino acids could be used for energy. When glucose is depleted as in a ketogenic diet, the body will turn to amino acids for energy more than normal. Amino acids are stored in muscle tissue, which means there is potential for muscle breakdown on this diet.

However this is only an issue during the initial phases of the diet, until the body becomes fat adapted. It is therefore recommended to consume a high protein diet during this time to supply sufficient amounts of amino acids for energy.

Once glucose is depleted and adequate amino acids are being consumed, most of the body’s tissues will use free fatty acids as their primary fuel source. The only exception to this is the brain, and this is when ketones come into action to meet the energy demand from this important organ.

During times of restricted carbohydrates the body adapts by producing ketones to ensure a fat derived fuel is available for the brain.

Other organs and tissues can use these too, but further adaptation by the body occurs so that free fatty acids become an exclusive energy source and so ketones are reserved by the brain.

Hormone Levels

What we first looked at is how the body will adapt based on the nutrients and substances that we give it via our diet.

This is what I consider the first level of understanding these processes, and the effect this has on us from a hormonal perspective is the second level.

Having a good knowledge of this and the part they all play help us to further understand the processes involved during a ketogenic diet.

The reason why the ketogenic diet works, its structure and the metabolic changes that occur as a result are based on the hormonal responses it creates.

As the ketogenic diet is based around the reduction of carbohydrates, it’s safe to say we are going to see a large down turn in the production of insulin. When we ingest carbohydrates, we typically see the largest increase in insulin levels.

Insulin is a peptide that is released from the pancreas to shuttle the increased levels of blood glucose to muscle, liver and fat cells in response to an intake of carbohydrates.

The key role of insulin is to manage blood sugar levels to ensure they remain in a safe and narrow margin (80-120mg/dl) in the body. Carbohydrates are the primary stimulant of insulin due to their high glucose content.

Protein and fats can also spike insulin levels, but normally not as much as carbohydrates. When insulin levels are kept low, such as within a ketogenic diet, another hormone called glucagon is released to manage low levels of blood glucose in the body.

Consider it the opposite of insulin.

Glucagon is also a peptide hormone released from the pancreas during times of low blood glucose levels.

The important point to note is when insulin levels reduce and glucagon levels rise, the body will break down stored fuels for energy. Triglycerides stored in body fat are broken down to free fatty acids, and protein may be broken down into amino acids.

Also, glycogen stored in the liver may be broken down into glucose. Therefore glucagon’s main role is to release the same energy stores that insulin transports for storage. Insulin is therefore considered anabolic and glucagon catabolic.

Of course, there are a number of other hormonal reactions that we see from consuming food or from not eating at all. For the basis of this article, and to avoid a short chemistry lesson, insulin and glucagon are the major players in the ketogenic diet.

The body’s ability to store and break down nutrients, it is not only based on whether glucose is being consumed in the diet, but a large consideration is also the level of glycogen stored in the liver.

When glycogen levels in the liver are topped up the body is more likely to store the incoming nutrients from the diet. This is still considered an anabolic state, as seen with high insulin levels.

When glycogen levels in the liver are depleted the liver will then start breaking stored nutrients into energy. This is considered a catabolic state, as seen with high glucagon levels.

When we combine low insulin levels (thus high glucagon) and depleted glycogen levels in the liver, we see a response from the body known as ketogenesis. This is the creation of ketone bodies.

Ketone and Ketodenesis

There are three ketones known as ketone bodies.

These are: 

  1. Acetoacetate (AcAc)
  2. Beta-hydroxybutyrate (BHB)
  3. ​Acetone

AcAc and BHB are produced from the consideration of acetyl – CoA, a product of incomplete breakdown of free fatty acids in the liver. Roughly one-third of AcAc is converted to acetone, which is excreted in the breath and urine.

In regard to someone following a ketogenic diet, the key role that these 3 ketone bodies play is to replace glucose as the primary energy source for the brain.

This process requires a shift in metabolism and is also known as fat adaptation. This is the body’s response to the lack of glucose in the body, so it can survive.

What is also seen in the first few weeks of such a diet is all body tissues using these ketones for energy too, as it serves as such a quick energy source. With further fat adaptation from these tissues, they slowly shift to free fatty acids. This usually occurs after 3 weeks on the diet.

As previously mentioned ketogenesis is the creations of these 3 ketone bodies when certain conditions are met and a hormonal response occurs as a result. This process is known to have a ‘lipolytic effect’ in the body, meaning it has a fat mobilizing effect, which is also known as ‘lipolysis’.

Lipolysis occurs in the liver and fat cells. The liver’s role is to regulate blood glucose levels in the body, so when carbohydrates are cut from the diet, its response is to break down glycogen reserves to replace this. Once these reserves are broken down ketogenesis is up regulated.

The rate at which the ketones bodies are produced appears to be related to the availability of free fatty acids in the body, and the liver becomes most efficient at this around 3 days into the diet. It typically then produces 115-180 grams of ketones per day.

Ketogenesis also occurs in the fat cells, and thus occurs when triglycerides (TG) are broken down into free fatty acids. These can be used as a direct energy source, and any reserves are passed onto the liver for ketone production.

You should now see how this whole process is linked and essentially serves as a survival mechanism for the body during times of depleted glycogen.

The following information can be summarised in the below diagram; 

The Adaptation Process

The following information summarises the body’s responses and adaptations during the initial stages of a ketogenic diet.

The process can be quite detailed and advanced, so those seeking more information should check the further reading section. 

The first 24 hours:

  • The body is still using energy from previous meals;
  • Roughly 50% of the body’s energy is from FFA after 10 hours without carbohydrates;
  • Insulin and glucose are decreasing, but glucagon and GH are increasing.

24-48 hours:  

  • The body starts to rely on FFA and the breakdown of liver glycogen for its energy requirements;
  • Liver glycogen is typically gone within 12-18 hours;
  • Increased use of amino acids, indicating increased protein breakdown;
  • The body’s use of glucose and protein is slowing down.

2-7 days+: 

  • Measurements of fuel use show that approximately 90% of the body’s total fuel requirements are being met by FFA and ketones by the third day;
  • The body is also increasing its own production of glucose to combat this during the initial week. This is known as gluconeogenesis (the making of new glucose);
  • Around the third or fourth day the body is in a state of ketosis;
  • By the second week the body down regulates gluconeogenesis as it adapts to ketogenesis;
  • The liver produces ketones at its maximum rate by day three;
  • Most tissues except the brain stop using ketones for fuel after the third week – instead they use free fatty acids;
  • It can take the brain a number of days in ketosis before it uses ketones for fuel;
  • Decreased amino acid breakdown due to decreased glucose requirements, nitrogen excretion and a more anabolic environment within the body;
  • After three weeks, the body may derive 93% of its fuel from FFA.

The Benefits and Drawbacks of The Ketogenic Diet

Protein Breakdown

A diet with carbohydrates has always been considered to be ‘anabolic’, mainly due to its effect on insulin, which essentially helps things grow.

Therefore a diet without carbohydrates is considered ‘catabolic’, meaning things won’t grow easily. This style of dieting is hence not ideal for those seeking significant changes in muscle growth or recovery.

There is also concern that particularly during the initial phases of the diet (the adaptation phase) that high level of protein breakdown can occur. This could therefore lead to a loss of muscle mass.

However, it has been shown that a protein intake of 1.5-1.75 grams protein per kilogram of lean body mass would spare most of the nitrogen loss.

Protein breakdown occurs as the body’s demand for glucose for energy goes up, but with time this demand decreases and protein breakdown is not as much of a concern.

It is suggested that regardless of bodyweight, during the first 3 weeks of a ketogenic diet, protein intake should be 150 grams daily. This can then be reduced to as little as 50 grams per day if required.

The opposite to this can also occur, as a ketogenic diet can become protein sparing once fully adapted. This is based on the reduced demand for glucose by the body.

It is therefore suggested that for those who lose lean body mass during calorie restricted periods, a ketogenic diet may be a good option.

Fat Loss

As we have done for every single protocol or diet we have covered so far, the question must be asked, does a ketogenic diet reduce body fat and improve body composition over traditional dieting models?

Many people believe that a ketogenic diet is superior for fat loss rather than a non-ketogenic diet. This isn’t strictly true and there is very little research to even show this is the case. 

What we do know is that ketogenic diets can be more effective at quick weight loss – there is a difference. Ketones are diuretic and many people can see initial weight loss of 5 pounds or more from water losses.

Also, glycogen is stored along with water in a ratio of three grams of water for every gram of stored carbohydrates. With a reduction in stored glycogen in the body, water is lost and further weight reduction occurs.

Essentially, as with any diet or protocol, true fat loss is dictated by the amount of calories consumed and there is no metabolic advantage to a ketogenic diet to bypass this.

If a ketogenic diet improves a person’s dietary compliance to help with their fat loss goals, then it is a suitable diet for them.


Some ketogenic diets report low blood sugar levels during carbohydrate refeeds or when they resort back to a more balanced method of eating.

The research has shown this to be the result of high levels of free fatty acids affecting glucose transport and utilization, thus resulting in increased insulin resistance.

Appetite Control

A diet low in carbohydrates yet moderate in protein and fat tends to create higher levels of satiety in people, mainly due to the slow digestion rate.

This tends to then lead to eating fewer calories in general, thus seeing improved fat loss. There is no research to suggest ketogenic diets suppress appetite in any other way.


The main driver behind high cholesterol levels and the associated cardio vascular diseases is mainly due to the consumption of refined carbohydrates and fats. Reducing these, like on a ketogenic diet, people tend to see a reduction in blood triglycerides.

With the focus on a moderate intake of healthy fats, an increase in HDL (the good stuff) cholesterol levels and decrease in LDL (the bad stuff) levels are reported.

Performance Levels

Due to the lack of glucose in the body high activity or exercise may not be sustainable on a ketogenic diet. Those who are active or exercising frequently should not follow a typical ketogenic diet as performance may decrease due to lack of energy.

The same applies for those who require a lot of mental energy or concentration daily; this diet may not be suitable.


As the ketogenic diet essentially eliminates carbohydrates from the diet, there is always room for potential deficiencies to creep in. Some ketogenic diets place focus on reducing vegetables, thus creating a reduction of micronutrients functions in the diet.

It is therefore beneficial to follow a ketogenic diet in the short term and implement a multivitamin and mineral supplement during this time.

As carbohydrates, particularly of the starch family are high in fibre, so ketogenic dieters can suffer from constipation. It may be beneficial to supplement with a high fibre foods during this diet.

Due to the reduced water storage within the body from a low carbohydrate diet, there is also potential for electrolyte imbalances; mainly sodium, magnesium and potassium.

For those suffering fatigue on a ketogenic diet, electrolyte supplementation may be beneficial. 

Setting Up A Ketogenic Diet Plan

When setting up a ketogenic diet for yourself or a client, it’s important to understand how various macronutrients and foods can affect or influence the ketogenic state.

Your goal is to always create and be in a pro-ketogenic state and thus minimizing nutrients that will be anti-ketogenic.

Hopefully the previous chapters of this article have highlighted the fundamental nutrient requirements to make this so, but below is a summary of the key nutrients and the considerations you must think about.


Protein is known to be pro and anti ketogenic. Protein can actually raise insulin levels, however this is not to the same effect as carbohydrates.

Nonetheless, this will inhibit ketogenesis, so total amounts of protein must be considered – too much and it will stop ketosis.

We have already established that protein will be required in the diet to stop amino acids being used from muscle tissue, and it has also been shown to stimulate glucagon release.


Fat is considered to be highly ketogenic with only around 10% of intake appearing in the bloodstream as glucose. 

Fat is therefore an ideal macronutrient in a ketogenic diet, however it must be noted that the amount of fat ingested will relate to the amount of fat lost.


All carbohydrates appear in the bloodstream as glucose, thus making it 100% anti-ketogenic.

A daily intake of more than 100g of carbohydrates is not ketogenic. This is because the brain requires up to 100g of glucose per day, so any more from carbohydrates means ketones are not required for energy.

Therefore, a ketogenic diet is one that has less than 100g of carbohydrates per day.

Once fat adapted (usually after 3 weeks), the brain’s requirement for glucose is approx. 40g per day, so daily carbohydrates must be reduced to stay in ketosis.


Alcohol is considered to have no effect on ketosis, but it has been shown to limit free fatty acids production in the liver and it does contain calories (7 kcal/g) thus reducing fat loss.

There is also evidence to suggest that high alcohol intake while being in a ketogenic state can lead to ‘alcohol ketoacidosis’.

This is when dangerous levels of ketones enter the bloodstream, but can be counteracted by the ingestion of carbohydrates.


Overall, water intake had no direct effect on ketosis, and a high water intake is recommended to counteract the natural dehydrating effects of ketosis.


Caffeine should have no direct effect on ketosis, but some have reported it could raise insulin levels indirectly. This may be of more importance for someone who is in the initial phases of ketosis.


Humans do not have the ability to fully digest fibre, meaning we do not get any calories from it, but it is a carbohydrate.

Therefore you should subtract fibre content from the total daily carbohydrate intake. However, a high fibre diet still may negatively affect ketosis, so it should be monitored. 


Despite the ketogenic diet being an advanced protocol, the actual application to apply it is simple.

It is possible to follow a ketogenic diet without tracking calories and macronutrients. Many ketogenic diets simply suggest reducing carbohydrates intake and eating as much protein and fats as required. This appears to work well.

To date it has been highlighted that carbohydrates must be below 100g for ketosis to occur, but many find this is still too many. In general, 30g or less is the ideal daily ceiling.

It is possible to take this diet a step further and track every single nutrient. This is advised for those who want faster results and to ensure they are reaching the calorie requirements necessary for their goals.

This would follow the same procedure as normal macronutrient plan creation, but limitation would be put on carbohydrates. Therefore higher percentage of protein and fats would make up the calorie intake. 


This article has provided you with a brief overview of the ketogenic diet, including how it works and how to apply it successfully. The following references and further reading are encouraged for those who wish to explore more into this advanced nutrition protocol.

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References & Further Reading


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