How Do You Get Into Ketosis?

The Path for Getting Into Ketosis
Body can use glucose, amino acids, fat, or ketones
to fuel your activities

On a low-carb diet, glucose, as a source of fuel, is often mentioned in the context of diet, but the body actually has four different types of fuel it can use to power your activities:
  • glucose
  • protein (amino acids)
  • fatty acids
  • and ketones
There's actually five, if you count alcohol, but I don't like to lump it in with the others, since the body perceives alcohol to be poisonous and strives to get rid of it first.

Your metabolic state pretty much determines how fuels are stored, as well as the proportions of how they are used.

The key to fuel utilization is carbohydrate availability.

When carbs are available in adequate supply, the body prefers to use glucose for its energy needs. 

When carbohydrates are restricted, the body can use other things to fill in, so it's generally understood by the low-carb community that carbohydrate isn't a necessary nutrient because the body can adapt itself to a different form of fuel, if needed.

The body can also use a different metabolic pathway.

At least, for awhile, and it's that different metabolic pathway where folks stumble and present ideas about ketosis that are not correct. 

In this blog post, I'm going to share how you get into ketosis to the best of my current understanding.

Pinterest Image: Blue and Gray Butterfly

So How Do You Get Into Ketosis?

The amount of glycogen that your liver stores to keep your blood sugar regulated is quite small. It amounts to the equivalent of about 80 grams of carbohydrate.

Although, both glucose and some amino acids can be turned into glycogen when needed, if your glycogen stores are full, there is only enough glucose to fuel your body for about one day.

Almost everyone can get into ketosis in as little as one day.

By restricting your carbohydrate intake to 20 carbs per day and, thereby, lowering glucose availability, you can shift your metabolism from burning predominantly glucose, to burning predominantly fatty acids and ketones.

If certain amino acids are in rich supply, the body will burn those too. Otherwise, it will strip your muscles for the amino acids it needs, once glucose begins to run low.

Initially, when your carbohydrate intake falls short, the body will use certain amino acids for fuel. It can directly oxidize these amino acids, so they don't need to be turned into glucose unless the body doesn't have enough glycogen to keep your blood glucose level steady.

The requirement for dietary protein at the beginning of your low-carb diet is higher than it otherwise would be, to cover the extra protein oxidation going on. This is why I'm always insisting that you eat enough protein.

You don't want to provide less protein than your body needs during the first two to three weeks of your weight-loss plan, or it will get those amino acids by breaking down muscle tissue instead.

Once the body switches over to using fats as a predominant fuel source, your protein need will go down and you are said to be in ketosis.

What Happens to the Brain when Glucose is Short?

Most of the body's tissues can use fatty acids for fuel, when available. But not all of them. The brain, red blood cells, bone marrow, and some muscle cells need glucose, even when you're in ketosis.

However, the brain can use ketones for up to 80% of its fuel needs, if they are readily available.

Ketones cause the brain's need for glucose to drop tremendously once you get firmly into the state of ketosis and things are running smoothly, about 3 to 4 weeks into your low-carb diet.

The liver, however, cannot use ketones for fuel. At all.

The liver runs on fatty acids, which makes sense, since ketones are the by-product of fat metabolism. And fat metabolism occurs in the liver.

By day three of carbohydrate restriction, glucose and amino acids are beginning to be replaced with fatty acids and ketones. BUT as ketosis continues to develop, most tissues which were initially using ketones for fuel no longer use them.

Instead, they switch from ketones to fatty acids, so the brain can have the ketones and glucose it needs.

This is generally referred to as being fat adapted, but some people refer to it as ketone-adaption. It requires the muscles to become insulin resistant, so they don't pull in the glucose from the bloodstream, leaving that glucose for the brain and cells with no mitochondria.

Insulin Isn't the Bad Guy

Insulin is generally considered the bad guy within low-carb circles, but it is a useful hormone.

There is no point fearing insulin. 

Without insulin being secreted you would die.

You need Insulin. It is an essential hormone. You just don't need an excessive amount of it, and you want your body to respond to the insulin you do make.

Insulin's job is to keep your blood sugar stable within a fairly narrow range.

Normal range can fall anywhere between 80 and 100 mg/dl, so when blood sugar rises above that margin, the pancreas releases it's stored insulin into the bloodstream.

This first-phase insulin secretion tells the cells that glucose is in ample supply, so it needs to pull the glucose in faster.

When cells take the glucose into their cellular structure, the concentration of glucose in the blood returns to normal within two hours, or nearly so.

Carbohydrate produces the greatest rise in blood sugar, even though protein will increase blood sugar to a certain extent.

If glucose didn't rise, there wouldn't be enough insulin secreted to get the amino acids and other nutrients into the cells.

When blood sugar drops, due to exercise or carb deprivation, insulin levels also drop. When insulin drops, glucagon increases, so the body becomes catabolic and begins breaking down stored fuels.

Glycogen stored in the liver is immediately broken down to create glucose, due to the presence of glucagon, and then the glucose is released into the bloodstream to bring the sugar level back up to normal.

Protein is also broken down into amino acids and used to rebuild protein structures or oxidized directly for energy. Triglycerides are mostly stored right away, but can be broken down into free fatty acids when needed.

The point of all of this is to get the blood sugar back to normal. This is the goal of the body and what it strives to always do.

How Ketones are Produced

This shift from insulin to glucagon a couple of hours after meals also initiates the production of ketones, since ketones are the incomplete breakdown of free fatty acids in the liver.

Ketones are a back-up system for the brain and other body tissues, which can use them initially.

Out of the three kinds of ketones produced in the liver, 1/3 of the acetoacetate ketones (AcAc) are converted to acetone and excreted in your breath and urine.

This is not much compared to the number of ketones produced overall, but it's enough for some folks to believe in a metabolic advantage from the excretion. 

Ketosis is a survival mechanism that shifts fuel use away from glucose and towards fat. In a sense, ketosis itself is starvation mode because the absence of glucose triggers it. The body believes that food is scarce.

Ketosis is what the body does to protect its protein losses (muscle mass), and to generate fuel when not enough food is coming in to maintain normal blood sugars.

This is the exact same thing that the body does during starvation or fasting. It's the same pathway, the pathway designed to save your life during a famine situation.

The major determinant of ketosis isn't fat intake as most low carbers suppose, but the level of glycogen storage in the liver.
When the liver runs out of glycogen, it starts the process of ketosis, whether there's extra fat in the diet or not.

After ketosis begins, its the body's ability to break down fatty acids into ketones that determines the RATE of ketone production.

Body fat mobilization is limited, so you can only mobilize, break down, and use a certain amount of body fat each day.

Eating Lots of Dietary Fat Does Not Cause Ketosis

Dietary fat doesn't cause Ketosis.

A lack of glucose (carbohydrate restriction) in the diet is what drives ketosis.

Incoming fatty acids are stored temporarily, while carbs are broken down into glucose, but once that glucose is used, the most recent deposited fat is pulled out first.

Body fat isn't a storage depot.

Fat is always in flux.

It move in and out of your fat cells.

Triglyceride is stored in fat cells but it is removed again on a daily basis. This enables the liver to have the fuel it needs to drive the ketosis process.

Vickie Ewell Bio


  1. thanks, good info but is it healthy to stay in ketosis indefinitely?

  2. What about good fats? if i eat olive oil and avocados? is "good fat" bad for ketosis?

  3. Is ketosis healthy in the long run? Look at the Inuit. They do pretty well (only problem lack of vitamin D).

    Ketones are actually a superior fuel to glucose. As you may know, the burning of glucose in the mitochondria is a major source of oxidative stress. And this stress can be seen as the primary reason for ageing as it promotes inflamation. As oxidative stress can damage the respiratory chain in de mitochondria, this may very well be the trigger for creating cancer cells (they don't have mitochondria).

    One quality of ketones is that they reduce the oxidative stress.

    So, if you don't want to age too quickly, want to avoid neurodegenerative diseases like Alzheimer, and want to reduce the cancer risks, ketones are the way to go.

    I could tell you so much more about the wonders of ketosis. For me it is the natural state, as it was for our paleolithic ancestors.

  4. Can you please give a sample daily diet, as I have been following a very low carb-high protein diet for some time and never seem to ket into ketosis let alone lose any weight. What am I doing wrong? Also would a diet pill like Duramine help at all??


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