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: the human body can only store a limited amount of glucose as glycogen. Most estimates calculate that the average body can only store about a half day's worth of energy as glycogen (the range is around 1000-1600 calories, depending on how much muscle mass one has).
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 and eat. 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 measly 1000 calories of stored glycogen are burned up? How does your body keep going when your glucose or glycogen reserves are low and no new fuel is coming in?
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 as your blood sugar and insulin drop, and more fat is released from the fat cells, your liver starts creating molecules called ketones or ketone bodies.
These ketones can be used by your muscles, heart and brain in place of the missing glucose, thanks to the body's ability to switch metabolic pathways on the fly.
In short, since you've used up all your stored glycogen and you don't have any new food coming in, glucose and insulin levels drop, ketosis kicks in and your body is switches over to using 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 glucose by lunch time and not had any energy to run down dinner, or even think about getting dinner. The human race would have been starved into extinction right out of the chute.
And not so coincidentially, 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 stored fat (in the form of triglyceride) is called upon to be metabolized for fuel, a substance called hormone sensitive lipase (HSL) breaks triglyceride down into a molecule of glycerol and 3 fatty acid molecules. These fatty acid molecules come in various lengths of carbon chains.
The fatty acids then flow into either liver or muscle cells and are transported into the mitochondria of the cell to be metabolized carbon by carbon in a process called beta-oxidation.
As glucose levels fall and fatty acid levels in the blood rise, the liver cells ramp up beta-oxidation which increases the amounts of a molecule called acetyl-CoA. As levels of Acetyl-CoA rises, it is shunted to a process called ketogenesis. Ketogenesis generates a ketone body called acetoacetate first, and this ketone is then converted into the two other types of ketones: beta-hydroxybutyrate, and acetone.
Meanwhile, the glycerol part of the 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 its own tissues to create glucose for the brain. This is because without some glucose, the brain will die and take you with it.
This brain glucose need is the main reason that registered dietitians insist that carbohydrates are necessary in the diet to support brain function. But this is incorrect, biochemically speaking, because they neglect to take into account that the body has a "secret weapon" called ketosis.
Ketones made from the products of fatty acids can be used by the muscles, heart 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 thing to remember about ketosis is that it 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 or lower depending on insulin resistance levels) 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 needed by the brain.
Starvation is a Different Scenario
Now, in real starvation scenarios, where people go for months without food, real problems start happening when glucose is needed, because truly, no fuel is available.
After several weeks or months without food and after 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 from starvation (unless there are other complicating health issues).
Aside from total starvation, in normal fasting states, most people have plenty of fat stores (100,000 calories on average), and the 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. The symptoms of ketosis vary with individual experience but they are not dangerous.
Unless you are a Type 1 diabetic (meaning your pancreas makes no insulin at all) or a Type 2 diabetic with a really burned out pancreas, ketosis is kept in check by the presence of insulin in the body. Insulin regulates the flow of fatty acids from our fat cells. As long as insulin is circulating within the body, in general, the flow of fatty acids and the production of ketone bodies is highly regulated and limited to a range that is 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.
This 2013 paper talks about the benefits of ketosis for many varied health conditions. The abstract states:
Very-low-carbohydrate diets or ketogenic diets have been in use since the 1920s as a therapy for epilepsy and can, in some cases, completely remove the need for medication. From the 1960s onwards they have become widely known as one of the most common methods for obesity treatment. Recent work over the last decade or so has provided evidence of the therapeutic potential of ketogenic diets in many pathological conditions, such as diabetes, polycystic ovary syndrome, acne, neurological diseases, cancer and the amelioration of respiratory and cardiovascular disease risk factors. The possibility that modifying food intake can be useful for reducing or eliminating pharmaceutical methods of treatment, which are often lifelong with significant side effects, calls for serious investigation. This review revisits the meaning of physiological ketosis in the light of this evidence and considers possible mechanisms for the therapeutic actions of the ketogenic diet on different diseases. The present review also questions whether there are still some preconceived ideas about ketogenic diets, which may be presenting unnecessary barriers to their use as therapeutic tools in the physician’s hand.
And these papers also describe the benefits of ketosis here, here and here. Also, just recently, Dr. Jeff Volek and Dr. Steve Phinney did a great interview on nutritional ketosis. It's long but worth watching.
And here's another great video of Jeff Volek speaking on keto-adaption.
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".
and this Volek and Phinney book is a good introduction the science of ketogenic diets.