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Ketogenic diets – an introduction to very low calorie diets for fat loss

One topic that has received a lot of airtime with the fervor of the low carbohydrate debate is ketosis and ketogenic diets. A ketogenic diet is simply one that induces a state of ketosis. While the details of this physiological function are intricate and numerous the point of this article is, as always, to break it down, simplify and to present a concise package for our readers.

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What is Ketosis?

  • a state of elevated ketones in the body
  • the liver produces ketone bodies from fat and protein stores when glycogen (carbohydrate) stores are low
  • ketone bodies are used as an energy source and a preferred option for the brain
  • this process is a normal physiological (survival) response to starvation
  • nutritional ketosis can also be achieved through a low calorie, low carbohydrate ketogenic diet
  • ketogenic diets have been used to treat epilepsy and show some potential for treatment of obesity

peanut galleryThat is ketosis in a nutshell but I will expand on these points a little more. Hopefully that will allow for a decent conversation around the dinner table for all meal revolutionists and Bantings. I will save the metabolic and athletic implications for another day though.

Ketosis is a natural process that allows humans to survive at times of starvation when our preferred source of energy (glucose) is not available. We would only last 2-3 days without food if we relied solely on carbohydrate stores. Instead we are able to use both fat and protein. In order to use protein however we need to break down muscle. Our muscle stores are also limited and to prevent debilitating wasting our body is able to preferentially use fat for energy. Essentially the greater the amount of fat stores the longer one would be able to survive during starvation.

In my research for this article I cam across this case study from 1973 where a young man underwent a medically supervised fast that lasted 382 days. He consumed only non-caloric fluids and was supplemented with vitamins and minerals. He lost 125 kg with no apparent serious concern or side effects. He was also able to roughly maintain his weight for a 5 year period after this marathon starvation although I would love to know what happened further down the line with his weight as well as other health markers.

During the first few days of starvation stored carbohydrate is utilised for energy through the breakdown of muscle and liver glycogen (stored glucose). Once these levels are low and no external carbohydrate is being eaten the body begins to use fat to produce energy. Our muscles and most organs are perfectly able to use fat as an energy source however our brain is not one of them. As the brain is responsible for about 20% of our energy requirements a reliable source of energy is needed. Ketones and ketone bodies provide this. They are converted from fat and used for energy production.

Two ketone bodies of interest here are acetoacetic acid and beta-hydroxybutyric acid which can be used to produce this energy to keep us alive. A third, acetone, is converted from acetoacetic acid and is responsible for the bad breathe and measurable urine ketones in a ketotic individual.

This use of fat stores for energy production that is characterised by ketosis is at the core of ketogenic diets for weight loss goals. If fat can be used as the primary source of fuel we should see fat loss. That is simple enough.

Such extreme starvation diets are not the only way to induce ketosis however and a few more tolerable methods have been developed. The term nutritional ketosis has been coined and used as a treatment for obesity. Naturally these are very low in calories (<800 kcal/day), low in carbohydrate (< 50 g/day), moderate in fat and moderate in high quality protein. Weight loss is usually rapid although some side effects and adherence to a successful protocol are concerns with such programmes. In addition a common loss of muscle mass reduces basal energy expenditure and increases the likelihood of weight regain once a regular diet is resumed.


A recent 12-month supervised trial however showed very impressive and sustained weight loss results using a ketogenic diet. Usually these diets have poor long term outcomes because they are not followed up correctly or progression back to a balanced diet receives little attention. This particular model induced mild ketosis through a 30-45 day restriction. Achieving 80% of the target weight loss initiated a gradual progression back to a low calorie, balanced diet. The benefit of regular contact sessions, counselling and exercise undoubtedly played a significant role too. As did the provision of foods suited to meet the dietary goals. The authors also noted a successful maintenance of lean muscle, a sign that muscle wasting was limited. They postulated that this was due to sufficient provision of high quality protein as well as the inclusion of an exercise regimen.

Variations on this very low calorie ketogenic approach are the backbone and theory to a number of weight loss diets. I would like to point out a few crucial elements however that may distinguish this from other trendy diets.

  1. There was a specific target group i.e. obese individuals
  2. The diet was seen as a form of treatment
  3. The programme was multi-factorial and included medical, nutritional, psychological, educational and exercise components
  4. A team of health providers was used
  5. A clear plan and strategy for progression existed
  6. Regular contact sessions reinforced the plan
  7. There was a long term outlook
  8. There was a goal to achieve both a significant weight loss AND a return to a balanced diet

Ultimately it was a successful trial for these reasons. As we will continue to see there are a number of ways to lose weight and the more encompassing the approach the better likelihood a positive outcome is. For extreme cases very low calorie ketogenic diets appear safe and effective over the long term when used as a multi-factorial model.

To end off it is important for me to discern the difference between ketosis and diabetic keto-acidosis (DKA). These are two very different states but commonly confused as the same thing. DKA is the result of low glucose levels inside the cells of the body due to the absence of insulin. It is insulin’s job to move glucose from the blood into our cells. Without glucose being absorbed into the cells the body assumes there is not enough glucose present, regardless of blood levels. As such glucose is continually produced from available liver and muscle glycogen with rising blood glucose levels manifesting. Fat is also mobilised to provide energy as explained earlier which results in an associated production of ketones as well as a state of acidosis. The process is a vicious cycle but impossible to overcome without insulin. This inadequate insulin production is only seen in type I diabetic patients and in some insulin dependent type II diabetics. The result of all this and the accompanying metabolic disturbances are dangerous, even fatal.