Ketosis: Survival over Starvation
Ketosis is a cellular process which gets ramped up when you switch to eating a low carb, ketogenic diet. It's actually part of the normal metabolic pathway which converts the food you eat into the energy that runs your body. Eating a higher fat diet just enhances this normal and safe chemical reaction.
Here's an explanation of why fat is better than sugar when it comes to body fuel.
Your Body on Sugar
Your body can run on several different types of fuel that come from your food. These fuels can be created out of any of the nutrients present in food: carbohydrates (carbs, for short), fats or protein.
When you eat high carb foods or large amounts of excess protein, your body breaks the food down into a sugar called glucose.
The glucose is then used as a fuel in each of your trillions of cells to create an energy molecule called ATP (adenosine triphosphate) which is needed to drive your daily activities and maintain your body.
Most of your food gets used up just maintaining and running your body on a daily basis. But if you eat enough food to avoid hunger, there will likely be some excess glucose available.
Two things happen to any excess glucose that your body doesn't use for energy right away:
Important Fact to Remember: your body can only store a small amount of glucose as glycogen. Most estimates calculate that your body can only store about a half day's worth of energy as glycogen (which amounts to about 1000 calories).
The Power of Fat over Sugar
So, imagine that you are a member of a hunter gatherer tribe in ancient times. No grocery stores are available, and you have to hunt down and catch the food that you eat.
Unfortunately, for the past two days, you haven't found any food animals to catch. No rabbits, no antelope, nothing. You are eating grass and leaves at this point, which are mostly fiber. You are in starvation mode.
What happens after your 1000 calories of glycogen are burned up? How does your body keep going when you don't have any glucose or glycogen left?
That's when ketosis happens.
During times when you can't eat (like when you are sleeping, when no food is available, or just when you are busy) your body switches over to burning the fat stored from last week's mammoth (or twinkie) binge, and creates molecules called ketones or ketone bodies.
The ketones can be used by your cells in place of the missing sugars, thanks to the body's ability to switch metabolic pathways on the fly.
In other words, since you've burned up all your stored glycogen, and you don't have any new food coming in, ketosis kicks in, and your body uses the fat that was stored from a previous meal to fuel itself.
If you think about it, ketosis is the logical consequence of evolutionary biology. Think of the caveman's food situation, and consider the fact that only small amounts of glucose can be stored as glycogen for fuel.
What would have happened to the human race if we didn't have ketones to burn when we couldn't find any food for a week?
Our hunter gatherer would have run out of stored sugar by lunch time, and not had any energy to run down dinner! The human race would have been starved into extinction right out of the chute.
And in fact, researchers have discovered that the body and brain actually prefer to burn ketone bodies over glucose, which makes perfect sense when viewed from the caveman's point of view.
Ketosis and Ketones To the Rescue
So how does our body make ketones out of the stored fat?
When a fat molecule is taken out of the fat cell and broken down by the liver, a molecule of glycerol and 3 fatty acid molecules are released.
The fatty acid parts of the fat molecule are broken down bit by bit, and in a process called ketogenesis, an assortment of ketone bodies are created. There are several types of ketones: acetoacetate, delta-3-hydroxybutyrate, and acetone.
The glycerol part of the broken down fat molecule gets converted into glucose in a process called gluconeogenesis, which means "make new sugar".
During times of fasting, gluconeogenesis is one the liver's most important jobs. Glucose is especially important for your brain function, and your liver will always make sure your blood levels of glucose stay within a narrow range, no matter what.
When a person is starving, the body will burn up fat and muscle tissue to create glucose.
This is the main reason that registered dietitians say that carbohydrates are necessary for brain function. But this is incorrect, biochemically speaking, because the body has a "secret weapon" called ketosis.
Ketones made from fat can be used by the muscles and brain to make energy when glucose is scarce.
This is important because it means that the brain is not solely dependent on the presence of glucose to operate. If you eat less carbohydrate, your brain can switch over to burning ketone bodies instead of glucose for fuel, which means your liver doesn't need to burn muscle tissue to make glucose for the brain.
An Important Note
The caveat of ketosis is that is takes a few weeks for the body to become "keto-adapted" and switch to burning ketones for fuel, once carbohydrate consumption is lowered.
Also, carbohydrate intake levels have to be lowered enough (below 60 grams per day) for ketone bodies to be made at a level that the brain can use. If you only lower carbohydrate intake a little, then the ketotic process gets short circuited, and can't do its job of taking over as a fuel source.
Most unfavorable low carb studies which reported the "unhealthy effects" of a low carb diet were actually poorly designed, in that they weren't long enough to account for the "keto-adaptation" period, and they didn't cut carbohydrate intake low enough to ramp up ketosis to the protective amounts.
Starvation is a Different Scenario
Now, in real starvation scenarios, where people go for weeks or months without food, real problems start happening when glucose is needed, because truly, no fuel is available.
After several weeks without food, and when fat stores are exhausted, the body will start converting the protein in the muscles to glucose, and muscle wasting begins.
You've seen the pictures of concentration camp survivors. Their bodies are literally just skin and bones, because all of the fat stores and muscles have been used up to make glucose for the brain to survive.
Note that in this scenario, the starved person was able to survive for many months without food because fat stores could be used for energy. It's only when all fat and muscle tissue has been exhausted that death results.
Aside from total starvation, in normal fasting states, most people have plenty of fat stores, and that ketogenic process helps us preserve muscle tissue by using ketosis and the ketones created for cellular fuel instead of glucose.
Ketones in the Body: Are they Dangerous?
So now we know that ketone bodies are the products of fat metabolism, and that they help the body maintain its muscles when no food is available.
Some people, including doctors, get the dangerous condition of ketoacidosis confused with normal benign dietary ketosis but they are different conditions.
Normal ketosis is NOT dangerous. Every person alive goes into a mild, normal ketosis, each time they go without eating for 6-8 hours. Ketosis symptoms vary with individual experience, but they are not dangerous.
In fact, ketosis and ketone bodies are actually quite beneficial to the body. In this paper, scientist Richard Veech writes:
"Surprisingly, D-beta-hydroxybutyrate...may also provide a more efficient source of energy for brain per unit oxygen, supported by the same phenomenon noted in the isolated working perfused rat heart and in sperm. It has also been shown to decrease cell death in two human neuronal cultures, one a model of Alzheimer's and the other of Parkinson's disease. These observations raise the possibility that a number of neurologic disorders, genetic and acquired, might benefit by ketosis.
How Do I Check for Ketosis?
If you have started a ketogenic diet and want to be able to check your ketone levels, there are several ways to do this.
You can buy ketone stix, and check the levels of ketones in your urine. This method has been the most common method for years, but recently, several companies have developed a blood ketone meter for home use.
This method of checking ketones in the blood is much more accurate, but is also much more expensive. Jimmy Moore has a nice post on using the blood meters here.
Below are links to the Keto-Stix for urine checks, and the various brands of ketone meters for blood checks.
If you would like to read more, Jeff Volek and Steve Phinney discuss the new method of checking blood ketones in their book "The Art and Science of Low Carbohydrate Performance".