What is Keto? – Introduction To The Ketogenic Diet

Ape in Contemplation of Keto?

By Josh O’Leary

You may have recently started to hear the term “keto” pop up in media or your life more generally. Keto is fast becoming the next big thing in the weight loss world with everyone from Susan at the office to celebrities like Halle Berry “going keto” and spreading the word on this “miracle weight loss regime”.

But what is keto? Is it a considered, healthy approach to eating or just the next fad that will be forgotten this time next year? What are the potential benefits and risks? Is it even effective for weight loss? These are the questions that I’ll attempt to tackle in this Intro to Keto post.

Before we dig in to the science, I want to start with a little information about my relationship with the ketogenic diet. I was first introduced to the ketogenic diet five years ago, around the same time as I was completing my qualification in personal training. I discovered it while researching the potential benefits of fasting and found the information was quite compelling. However, what I was being taught on my course did not match what I was reading online.  The nutrition component of the course was admittedly brief, but the section on ketosis was no longer than the following sentence:

“Ketosis is what happens to your body when you consume to much protein. It makes your breath smell and if it goes too far can lead to diabetic ketoacidosis.”


Completely wrong!

I knew immediately how wrong this lesson was and I was therefore able to promptly ignore it. Since then, I’ve continued my research in to the ketogenic diet, experimented with entering a ketogenic state personally for different lengths of time and felt the potential pros and cons of this way of eating.

Luckily, public awareness of the ketogenic has also improved, with more and more people introducing it in to their lives and feeling the positive effects, but of course this has come with an inevitable backlash from the health establishment and conventional media, who continue their insistence on the importance of a “balanced diet” and “everything in moderation”.

Who is right? I want you to decide for yourself but in order to make a well-informed decision, you need to be well informed.

Let’s get in to some science!

Energy in the body

Your capacity to produce energy is absolutely astonishing. Every cell in your body is reliant on a single molecule called adenosine tri-phosphate (ATP), the breakdown of which is the source of all the energy we need to be alive. Every single day, the cells in your body break down and recycle roughly your body weight in ATP and any interruption in this process causes death in seconds (this is how cyanide kills you).

Because this process is so vital, we have evolved multiple methods of ATP production making us able to endure short-term disruptions in particular chains of reactions without sacrificing the production of ATP. This is why you can continue to produce energy for a short amount of time without oxygen, like when you are sprinting the 100m or swimming lengths under water.

The processes are far too complicated for me to tackle in a blog post, but it is helpful to understand to a certain degree how your body produces ATP for energy, especially in the context of a ketogenic diet, so I will simplify and distil this topic down to what you need to know.

Carbohydrates, Fat and Ketones

Most of the time, your cells are either “burning” carbohydrates or fat to produce ATP. In certain extreme situations, they might resort to metabolising protein to make energy but this is rare and only really occurs in starvation scenarios. Whether your cells are using carbohydrates or fat as their energy substrate depends greatly on what you teach them to use, but there definitely seems to be preferable states of metabolism. In a lean, healthy person with a well functioning metabolism, almost every cell in the body will predominately be using fat to make energy. There are a number of reasons for this but the most obvious one is that our bodies can store far greater amounts of fat than carbohydrates so it makes sense for us to be predominately reliant on the macronutrient that is available in greater amounts.

However, there are certain parts of the body that cannot use fat to make energy, the most important of which is the brain. There is a semi-permeable membrane between your bloodstream and your brain (the blood-brain barrier) which functions to stop nasty things from getting in to your brain. A side effect of this barrier is that fat cannot get through it and therefore can’t supply your brain with energy. For most people, this means that their brains are reliant on carbohydrates to act as the substrate from which they can produce ATP.

Here we run in to a problem.

The human body has a very limited capacity to store carbohydrates. In fact, the store of carbohydrates that is supposed to feed your brain only contains enough potential energy to keep your brain functioning for a couple of days. Three at a push.

So what happens if we work our way through this energy without replenishing it?

24/7, 365 access to food is a modern phenomenon. For much of our evolution, access to food was intermittent and dependent on external factors such as our ability to hunt and gather, weather and climate conditions and the migration patterns of animals. There would have been countless times in our shared past in which our ancestors needed to survive without food for longer than 3 days. In fact, they not only needed to be able to survive this period, they needed to thrive in this period. There is never a more important time for you to be functioning at full capacity than when you are a hunter who has gone days without food. You need your perceptions to be heightened and your focus sharp so that you can spot that half covered antelope print in the sand…missing it could mean death for your family.

For us modern folk, this sort of state can be hard to imagine. Many of us feel cranky after a few hours without food. Make us skip a meal and we feel dizzy and weak because of low blood sugar. This is because we have lost our ability to enter the metabolic state that kept our ancestors alive over millions of years.


If you were to stop eating right now and not eat anything for three days, you would not die.

You might feel like killing someone else, but you yourself would not die.

The reason for this is that you would enter what is called a ketogenic state. Your brain would eat its way through your liver carbohydrate stores and once they were fully depleted, you would start to send fat molecules (fatty acids) to your liver to be converted in to ketones. These ketones can travel through your blood stream and, critically, cross the blood-brain barrier in to your brain where they can be used by your brain cells for energy.

One of the really cool aspects of this process is that, depending on how much fat you have on your body, you can be in this state for a very long time.

Let’s do some maths to make this a little clearer:

  • Let’s take an 80kg man with 10% body fat (this is very lean)
  • 80kg x 0.1 = 8kg = 8000g (this is the amount of stored fat on his body)
  • 1g of fat produces 9kCals of energy when burned
  • 8000g x 9kCals of energy = 72,000 kCal

So just to put that in perspective, a man this size will on average burn around 2000 kCal a day, meaning he has enough potential energy in the form of fat – and therefore ketones – to keep him ticking along for over a month! But without that crucial ability to convert fat to ketones to provide energy to his brain, he would not be able to survive without food for more than a few days.

Is keto just another fad diet? I’d argue pretty strongly that without keto, none of us would be here.

The Ketogenic Diet

So far, I have described what is known as Starvation Ketosis, the process by which your body will produce ketones to keep your brain functioning when you have no access to food. This is one way for modern people to get themselves in to ketosis, and while fasting is becoming a popular weight loss and therapeutic strategy, it is not the only way to feel the benefits of having ketones in your brain.

You can eat a diet with a very particular set of macronutrient ratios that will induce ketogenesis (the production of ketones in the liver) after a few days; this is called The Ketogenic Diet. The diet itself is simple, but not easy. You must restrict your intake of carbohydrates to less than 30g a day (or 10% of your caloric intake), keep your protein intake “moderate” (usually this means up to 30% of your calories) and make up the difference in fat (60-80%!). If you stick to these ratios, you will deplete your liver carbohydrate stores, keep your insulin levels low and start making ketones.

Pros and Cons of Keto


The ketogenic diet has been known to have therapeutic neurological effects for nearly 50 years. The diet has been used effectively since the 1970s to treat children with drug resistant epilepsy. More recently, the diet has been shown to have positive effects on sufferers of Alzheimer’s, Parkinson’s and Traumatic Brain Injury. The exact mechanism by which the ketogenic diet has such a positive effect on these neurological disorders is still being studied but one thing is clear, brains work better on ketones.

This makes sense when we cast our minds back to those ancestors of ours who have been tracking a wounded antelope for three days with no food. It is of critical importance that these hunters have optimally functioning cognitive performance so that they can be successful in this hunt and this is what ketones provide…an optimally functioning brain. People who get themselves in to ketosis report intense concentration, incredibly consistent energy levels and laser like focus.

More recently, the ketogenic diet has been shown to reverse insulin resistance and is therefore thought to be a promising therapy in the treatment of disorders like Type-II diabetes and obesity (I will cover insulin resistance and fat loss in a future post).

It’s even been shown to be effect in the treatment of some cancers!


There’s no denying that the ketogenic diet can be hard to stick to. Even a small amount of carbohydrates can kick you out of ketosis and unfortunately we live surrounded by an abundance of tasty, carbohydrate-laden foods. Temptation is ever present and cravings can be hard to resist. This is especially true during the period of what is called keto-adaptation. This is the length of time that it takes your body to transition from being a carb-burner to a fat-burner and can last up to three weeks. During this time, people report being tired and cranky with strong carb cravings.

It also may not be the most effective diet to choose if fast weight loss is your top priority. Whenever you are consuming fat, you aren’t burning it, so some people find that the high fat recommendation in the ketogenic diet can produce slower results.

Should You Go Keto?

It seems clear to me that the ketogenic diet is not just a fad, although it is not surprising that it is labelled as such. It is an ancient metabolic process that allowed our species to survive paleolithic times and build modern civilisation.

Whether you choose to incorporate it in to your life is entirely dependent on context and your personal goals. Do you want to increase productivity at work through better focus and concentration? Do you have a family history of neurological issues? Do you want slow but sustainable weight loss? If you answered yes to any of the above, I’d highly recommend trying it out.

Is fast weight loss your biggest goal? Do you participate in a highly glycolytic sport like rugby or Crossfit? Do you like to indulge your sweet tooth regularly? If so, then I’d look elsewhere. You can gain make a lot of progress towards becoming healthy simply by eating low-carb-high-fat (LCHF) without going full blown keto.

If I have piqued your interest, here’s three steps you can take to learn more;

  1. Read The Art and Science of Low Carbohydrate Performance, a book considered the bible on all things keto.
  2. Check out peterattia.com – this guy knows his stuff
  3. Sign up to our online course. There you will learn how to transition your body away from burning carbohydrates and towards becoming a fat-burner. The course also contains a module on cognitive performance in which I describe the exact steps you could take right now to get in to ketosis as quickly as possible.

Want to know more? Sign up here to receive a free module from our online course! Learn how to use a keto diet to improve your Cognitive Performance

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