Ketosis Basics, part 1

What is ketosis?

Ketosis is the state in which your body shifts from primarily utilizing glucose for energy to utilizing ketones (ketone bodies) for energy.  Ketone bodies are produced from the breakdown of fat (fatty acids) and thus are present when one’s glucose supply is diminished, such as after prolonged exercise or a period of fasting.  The vast majority of the time, our bodies are utilizing glucose from carbohydrates as an energy source, producing ATP, the energy source for all living cells, via the process known as cellular respiration which you may recall includes glycolysis and the Krebs (citric acid) cycle.

[Fun fact: Depletion of ATP is what causes rigor mortis following an organism’s death.]

We do not have an unlimited supply of glucose stored in our bodies, and thus the ability to use fatty acids as fuel gives us great flexibility by allowing us to tap into our abundant energy stored as fat.

We can store only about 2,400 calories of carbohydrates, which places a limit on our ability to endure prolonged physical activity.  Endurance athletes, such as long-distance runners, traditionally carb-load the night before an event, eating a large amount of carbohydrates to replenish their glycogen stores, only to later “hit the wall”, or “bonk”, during their race – a situation whereby they deplete their glycogen (stored glucose) stores and then are unable to tap into their fat stores for energy.  This situation is equivalent to a tanker truck carrying thousands of gallons of gasoline running out of fuel in the truck’s gas tank – the fuel in the trailer is of no benefit to the truck because it’s inaccessible.

It would be a poor design for our bodies to be totally dependent on carbohydrate metabolism for survival, especially with such little energy available from carbohydrates.  When glucose is not available, our bodies start tapping into our fat stores, which contain many times the available energy that we are able to store as glycogen.  When fat is broken down for energy, the useful ketone bodies produced are acetoacetate and β-hydroxybutyrate.

Here’s more detailed information for those interested in the biochemistry of ketones.


Why would I want to be in ketosis?

There are many recognized benefits of nutritional ketosis.

Utilizing fatty acids as a fuel source obviously depletes the amount of fat stored in our bodies, resulting in fat loss [i.e. weight loss].  The metabolic benefits of a low-carbohydrate diet are far-reaching and definitely not fully appreciated, including improving all components of the Metabolic Syndrome and reversal of diabetes.

Science supports many benefits of ketosis:

  • Ketogenic diets have been recognized as “a proven therapy for drug-resistant epilepsy”
  • There is evidence supporting the use of the ketogenic diet as an adjunct in cancer treatment.
  • There is evidence from a randomized controlled trial demonstrating that increased blood ketone levels resulted in improved cognitive scores in individuals with mild to moderate Alzheimer’s Disease.
  • In a rat heart model, ketone bodies improved the efficiency of cardiac function by 25%.
  • In a mouse model, diabetic nephropathy was completely reversed by a ketogenic diet.
  • treatment of epilepsy,
  • Case studies suggest a potential link between a ketogenic diet and improvement in mental health disorders such as schizophrenia and autism.

For me, personally, I find the metabolic flexibility to be the most rewarding part of ketosis in the short-term setting.  I am no longer a slave to food nor to conventional meal times.  Ketosis suppresses one’s appetite, and thus I can skip morning and noon-time meals without difficulty, waiting to savor a delicious dinner on my own terms rather than rushing to eat before or during my workday.  I frequently work right through lunchtime while being amused at the site of others racing to and from the cafeteria, often stressed and carrying food back to their departments.

It may be annoying to those who struggle with it, but I appreciate the easy fat loss, too.  I used to eat a low-fat diet – blindly following what I was taught in my training.  Aside from that being gravely wrong, I found that I could only lose weight by performing a huge amount of vigorous exercise including weights and cardio.  That may work for some, but it just isn’t sustainable with my work schedule.   Furthermore, I am motivated by the reassurance that there are many profound long-term benefits in regards to not only my heart health and brain health, but to my overall health.  If you knew you could prevent a heart attack, stroke, or dementia with a simple lifestyle change, wouldn’t you commit to that change?

  • Masino, Susan A., ed. Ketogenic Diet and Metabolic Therapies: Epanded Roles in Health and Disease.  Oxford University Press, 2017.



Ketosis vs. Ketoacidosis

It’s important to clarify that nutritional ketosis is an entirely safe and normal physiological state characterized by the presence of ketones in response to low carbohydrate intake.  Many people erroneously confuse “ketosis” with “ketoacidosis”, a very different pathological condition.  Ketoacidosis is a condition characterized by the unregulated breakdown of fatty acids in the setting of insulin deficiency that results in exponentially higher levels of ketones than one can experience with simple nutritional ketosis.  The difference between these two conditions is unmistakable – a person in ketoacidosis is severely ill, whereas a person in nutritional ketosis is just fine and may well be thriving.

Read here for more.


How can I get into ketosis safely?

The key to getting into nutritional ketosis is carbohydrate restriction, ideally less than 20 gm daily, which is slightly more than 1 slice of bread.  Yes, that is not a lot of wiggle room for carbs, and yes, it is worth it.  Never fail, when I tell someone about eating so few carbohydrates per day, they say something to the effect of, “Oh, I could never do that” or “No way, I would die!”  Both are wrong.  I understand that food is a very emotional topic and that there are a lot of strong opinions about food; these statements simply reflect lack of awareness of what’s possible with the human body.

Our bodies are indescribably complex and amazingly versatile – you simply cannot go wrong by eating real food, no matter the amount of carbohydrate.  Most people have some manifestations of insulin resistance – abdominal fat, high blood pressure, high triglycerides, low HDL cholesterol, or high fasting blood sugar, polycystic ovaries, cardiovascular disease, etc., and thus would benefit greatly with a ketogenic diet.

Getting into ketosis is relatively simple, but it takes some preparation and some discipline.  First, you need to become “fat-adapted”.  Fat-adapted means that your body has learned how to utilize fat stores for energy.  You need to train your body to gain access to the fuel in the tanker instead of just what’s in the gas tank.  How do you do that?  Gradually decrease your carbohydrate intake.

Your first step should be to cut out all forms of sugar.  Get rid of regular soda, juice, and any added sugar.  That will require reading labels at first, but you will soon learn that nearly all packaged food items contain some form of sugar, often high fructose corn syrup, and that you are ultimately better off avoiding any packaged foods with labels.

Your body is probably accustomed to running on carbohydrates and thus if you suddenly cut out carbohydrates, your body will probably revolt against you, often in the form of weakness, fatigue, lightheadedness, headache, and brain fog.  This so-called “keto flu” is thankfully self-limited (usually 2-4 days), so you may just muscle through it and be reassured that you will feel much better on the other side.

Fat adaptation usually takes about 3 weeks for someone aggressively limiting their carbohydrate intake, longer if one is more insulin-resistant.  You’ll know you’re fat adapted when you can fast for an entire day without feeling faint or ravenously hungry.  It gets easier, I promise – it may feel like an insurmountable task at first, but be assured that your body’s physiology is not terribly unlike the other 6 billion people on earth and the billions that came before us.  Just like everyone else, there is absolutely NO physiologic requirement for carbohydrates.

“The lower limit of dietary carbohydrate compatible with life apparently is zero, provided that adequate amounts of protein and fat are available.” – Institute of Medicine, Dietary Reference Intakes, 2008.

WARNING: Use caution when attempting to fast for more than 12-18 hours if you are currently consuming a Standard American Diet (SAD).  Also, if you are on diabetes medications, you need to summon your doctor’s advice before making any significant changes to your carbohydrate intake.