Is Ketosis a myth?

Not it is not a myth.

In terms of cellular respiration, the body will preferentially use first glucose, then fat, and lastly protein for fuel. Protein is broken down into sugar for fuel. Ketones are water-soluble fuels used by tissues created during the metabolism of fat (triglycerides). "Ketosis" occurs when the levels of ketones in the blood become elevated.

Since the body will preferentially use glucose before fat, you can enter ketosis in three main ways: 1. fasting, 2. a carbohydrate restricted diet, or 3. prolonged exercise. In all three situations, the body depletes its available glycogen stores (within the liver and muscles), insulin levels drop, fat metabolism increases, and ketone bodies rise.

Most normal healthy people will enter ketosis after 12-14 hrs of fasting (usually during the break between dinner and breakfast). People who are insulin resistant, have elevated blood glucose and insulin, and snack constantly (before sleeping and upon rising), may never enter ketosis. There is no evidence of adverse effects associated with fasting or nutritional ketosis, and lots of increasing evidence for diverse benefits.

The benefits of ketosis go beyond simply burning fat. Fat metabolism is a cleaner fuel in terms of cellular respiration--less reactive oxygen species, less inflammation. It seems to have therapeutic effects on brain tissue (decreasing excitatory neurotranmitters and decreasing cell death: http://www.ncbi.nlm.nih.gov/pubmed/11569918), which probably explains why it has been an effective treatment for epilepsy for over a century.

Ketosis is not necessary for weight loss, but a lot of people choose it for the added benefit of appetite suppression. You can be in a ketogenic state as long as you are primarily burning fat for fuel; however, that fat can come from your stored adipose tissue or dietary fat. If your goal is weight loss, and you find yourself stalled on the ketogenic diet, you are mostly likely eating too much fat, which is more common with "keto" processed foods like sweetened fat bombs or shakes. It is much easier to control for the correct macros when eating fatty whole foods, coupled with protein and fiber (from low carb vegetables).

EDIT: I should also add that if you have trouble maintaining ketosis on a ketogenic diet (while restricting carbohydrates), you also may be eating too much protein and not enough fat--as protein is broken down into glucose. The ketogenic diet is low carb, high fat, moderate protein diet.

You'll find many people freak out over keto diets lol. I tried it but didn't really give it a good chance, I love fruit especially in the summer, and found it too restrictive. BUT I did love how I felt on it and will probably try it again. Google "OKL Chart", it tells you the optimal macros based on your height. I've also read as long as you keep carbs under 50g you'll stay in ketosis, the 20g limit is good to GET you started. There are many success stories out there so it does work!

SideSteel wrote: »

It's not a myth at all, however it's often misrepresented.

Fat loss is still going to depend on energy balance. A ketogenic diet is one way for people to get there, and some people do quite well on it.

As far as fat oxidation goes, you burn more fat on a ketogenic diet but you also eat more fat on a ketogenic diet. Differences in actual loss of BODY FAT aren't going to be significant when comparing a low carb diet to a higher carb diet if protein and total energy content of the diets are matched in comparison.

In real life though, we don't get to eat a lab controlled diet and so obviously you should go with whatever diet allows you the best adherence/dietary control.

To add onto this, one should follow a dietary strategy that addresses their goals and one they respond well to. Not everyone peforms well on low carb and not everyone is filled up by fats. This also works the other way. Not everyone does well on high carb.