What Is Ketosis?

Written by Sara McEvoy
on March 22, 2019

Interested in the ketosis craze? Unlike a lot of other food fads, this one has some merit to it. 

In this article, we're giving a broad overview of this nutrition program — one that's experienced a surge in popularity lately due to its ability to assist with weight loss (among other benefits). We'll discuss the definition of ketosis and a ketogenic diet, how to get into ketosis fast, signs that you're in it, and tips to help you optimize the nutritional benefits of this highly desirable metabolic state. 

So, What Is Ketosis?

We just used the term "highly desirable metabolic state." We'll expand on this a bit to give you our elevator pitch on what ketosis actually is:

Ketosis is a highly desirable metabolic state in which your body uses stored fat for energy instead using of dietary carbs. You can achieve ketosis in a few different ways, but the main way is by adopting a ketogenic diet (also known as keto). On a ketogenic diet, a person gets about 70% of their calories from fat, about 15% of their calories from protein, and 5% of their calories from carbohydrates.

Normally, your body breaks down carbs from your food into glucose molecules and uses this for energy. By drastically restricting carb intake on keto, your body eventually runs out of glucose. This causes your levels of insulin hormone to drop and triggers the liver to create molecules called ketones from stored fat. It's these ketones that your brain and body can now use for energy. 

Who Is the Ketogenic Diet For?

The ketogenic diet isn't new. It's actually been around for centuries and has been heavily studied by doctors and researchers. It's not for everyone, and if you have any medical conditions, it's a good idea to chat with your physician before making drastic changes to your diet or lifestyle. 

That said, lots of research has shown that ketosis is generally safe and effective, even for specific populations of people, including people who are obese, people with diabetes, and children with drug-resistant epilepsy. Most people use keto for rapid weight loss, but the benefits extend beyond this.

The Benefits of Ketosis

In addition to ramping up weight loss rate, ketosis and the ketogenic diet can also:

  • Decrease blood sugar levels, which may protect against diabetes and metabolic syndrome
  • Improve blood cholesterol (including lowering "bad" cholesterol and improving "good" cholesterol), which may protect against heart disease
  • Improve energy and mental clarity, which may boost athletic and cognitive performance 
  • Offer neuroprotective benefits, which may protect against Alzheimer's, Parkinson's, and other neurodegenerative diseases

More research is being done to determine the extent to which keto can benefit humans. 

A Note on Ketoacidosis and the Ketogenic Diet for People With Diabetes

One criticism about the keto diet is that it may increase certain people's risk for a dangerous metabolic state known as ketoacidosis.

Unlike ketosis, which is a natural and safe metabolic state that helps your body burn fat for energy, ketoacidosis is a medical emergency, and, if left untreated, this could lead to coma or death. This condition generally occurs in people with diabetes (typically affecting those with type 1 more often than type 2), hence its more common name diabetic ketoacidosis, or DKA.

Ketoacidosis develops when a person's insulin levels are so low that no blood sugar can get into the cells. Since this looks like "starvation" to the body, the body will begin breaking down fat into ketones at a very high rate. This can lead to a potentially deadly combination of very high ketone levels (far beyond what is considered ideal for ketosis) AND high blood sugar levels.

Symptoms of ketoacidosis include extreme thirst, frequent urination, vomiting, nausea, abdominal pain, confusion and mental status changes, rapid breathing, fatigue, dry mouth, and dry or flushed skin. 

Because ketoacidosis occurs when insulin levels are extremely low, people with diabetes (especially type 1 diabetes) are the most at risk for developing it on a ketogenic diet. 

But does this mean the keto diet isn't safe for people with diabetes? Not necessarily. In fact, research has shown that the keto diet can improve blood sugar and A1C (a person's average blood sugar levels over a two- to three-month period), reduce the need for insulin medication, and drive weight loss in people with type 2 diabetes. (The research on keto and people with type 1 diabetes is less conclusive.)

BUT (and this is a big but), the people in these studies were closely medically supervised in order to avoid the risk of complications, including DKA.

The bottom line is that anyone with diabetes needs to work closely with their physician before and while making ANY changes to their diet, medications, or lifestyle. This includes experimenting with a ketogenic diet. As part of a medically supervised medication and lifestyle regime, keto may be able to help a person manage their diabetes more effectively. 

Getting Into Ketosis: What to Expect

The previously mentioned benefits are typically seen once a person has been following a ketogenic diet for some time. During the initial switch from a diet rich in carbs to a diet rich in fats and low in carbs, it's normal to experience carb "withdrawal" side effects for a few days. This includes flu-like symptoms like muscle cramps, headaches, sugar cravings, and irritability (also known as keto flu). 

How long it takes to reach ketosis depends on the individual person, including how much body fat they have and what their resting metabolic rate is. Most people enter nutritional ketosis within a couple of days to a couple of weeks of adopting a ketogenic diet. 

As far as knowing if you're actually IN ketosis, there are two broad classes of data to assess this: subjective and objective. 

Subjectively, you can typically tell if you're in ketosis by looking for telltale ketosis symptoms. One of the common side effects is foul breath, often compared to rotting fruit. You may also notice increased energy, better sleep, less hunger, improved mood, and rapid weight loss. 

Objectively, you can test your urine or blood for the presence of ketone molecules. This is relatively simple to do with at-home urine strips and or blood testing kits, with the latter being more accurate and the former being a bit cheaper and easier. To be in dietary ketosis, your reading needs to be somewhere between 1.5 to 3.0 mmol/L of ketones in your blood, or show a darker color on the urine test strips. 

What to Eat (And What Not To Eat) on Keto

While there's no specific prescription for a ketogenic diet, most people following keto aim to consume less than 50 grams of net carbs per day and moderate levels of protein. The bulk of their calories (at least 70%) come from fat. 

To achieve this, you'll want to avoid or eliminate higher carb food sources like bread, pasta, and anything with added sugar. Instead, you'll want to eat things like healthy fats (including nuts and their butters), meat, poultry, fish, eggs, green veggies, and berries.

You can also increase your speed to reach ketosis by:

  • Limiting alcohol use
  • Experimenting with intermittent fasting
  • Drinking a lot of water
  • Getting enough sleep
  • Consuming supplemental exogenous ketones


This article was written by: Sara McEvoy

Sara McEvoy, PT, DPT is a licensed and board-certified doctor of physical therapy. She earned her degree in 2011 from Boston University. Sara is also a professional freelance writer and copywriter. She researches and writes almost exclusively within the health and wellness field.  

Written by Sara McEvoy

Published: March 22, 2019