Last Updated on January 23, 2025 by Arif Chowdhury

Have you recently started following a low-carb or ketogenic diet and found yourself wondering, “How do I know if I’m in ketosis?” It’s a great question and one that many people who adopt this lifestyle ask.

Ketosis is a natural metabolic state in which your body burns fat for fuel instead of carbs. But, unlike the everyday process of burning carbs, ketosis can come with some noticeable signs that tell you when you’ve entered this fat-burning mode.

In this article, we’ll walk you through the common indicators of ketosis, the science behind them, and how to check whether you’re in ketosis or not.

Plus, we’ll throw in a few fun facts along the way to keep you engaged. Let’s dive right in!

What is Ketosis?

Before we get into how to know if you’re in ketosis, it’s important to understand what ketosis is. When you eat fewer carbs, your body doesn’t have enough glucose (sugar) to use as energy.

In response, your liver starts converting fat into molecules called ketones, which your body uses for energy instead. This process is called ketosis.

Ketosis is a key component of the ketogenic diet, a popular low-carb, high-fat eating plan that encourages your body to enter this fat-burning state.

People on the ketogenic diet typically limit their carb intake to about 20-50 grams per day, prompting their body to shift into ketosis after a few days.

But how can you tell when your body has actually entered ketosis? Let’s explore some of the common signs.

1. Increased Ketone Levels in Your Breath, Blood, or Urine

One of the easiest and most reliable ways to confirm if you’re in ketosis is by measuring the level of ketones in your body. There are several ways to test for ketones:

• Breath: There are breathalyzers designed to detect acetone, a type of ketone that your body releases when it’s in ketosis. Breath tests are non-invasive, though they can be a bit pricier than urine strips.
• Blood: Blood ketone meters are the most accurate method for testing ketone levels. They measure beta-hydroxybutyrate (BHB), the most abundant ketone in your blood. A reading of 0.5 mmol/L or higher indicates mild ketosis, while 1.5 to 3.0 mmol/L suggests moderate ketosis. Anything above 3.0 mmol/L is considered high ketosis, which could be dangerous, so it’s best to stay within the lower range.
• Urine: Ketone urine strips are inexpensive and widely available. They measure acetoacetate, another type of ketone, but they can be less accurate over time as your body adapts to ketosis. Still, they can offer a quick and easy way to check.

Fun fact: Studies have shown that about 80% of people who are on a ketogenic diet show ketones in their urine after 3-4 days of restricting carbs. So, if you’ve just started the keto diet, you may notice the strips turning purple!

2. Bad Breath (aka “Keto Breath”)

If you’ve heard about “keto breath,” you might be wondering if it’s just a myth. It’s not. One of the more surprising and often unpleasant signs of ketosis is bad breath, which is due to the presence of acetone, a type of ketone that your body releases when it enters ketosis.

Acetone is released through your breath, and it can give your mouth a distinct fruity or metallic odor.

If you’re trying to figure out if you’re in ketosis, check your breath. Does it have a fruity, slightly sweet smell?

If yes, it could be a sign that you’re in ketosis. Keep in mind, though, that not everyone experiences this, and some people may not notice it at all.

Fun Fact: A study published in The American Journal of Clinical Nutrition found that 7 out of 10 people on the ketogenic diet reported changes in their breath, with the majority describing it as “fruity” or “nail polish remover” like.

3. Increased Thirst and Frequent Urination

When you enter ketosis, your body starts burning fat for fuel, and one of the side effects of this process is that it sheds water. This is because glycogen, the form of carbohydrate stored in muscles and the liver, binds to water.

When you stop eating carbs, your glycogen levels decrease, and your body releases this excess water, leading to increased urination. As a result, you might find yourself needing to drink more water and using the bathroom more often.

This is also one of the reasons why many people experience rapid weight loss during the first few days or weeks of the ketogenic diet, as water weight is shed.

Tip: Stay hydrated by drinking water consistently throughout the day. It can help minimize the effects of dehydration and reduce some of the common symptoms of ketosis.

4. Fatigue and “Keto Flu”

If you’re new to the ketogenic diet, you may experience a temporary period of fatigue, irritability, headaches, and dizziness.

This is commonly referred to as “keto flu,” and it typically happens within the first few days of drastically reducing your carb intake.

The symptoms of keto flu are thought to be related to the body’s adjustment to burning fat for fuel instead of glucose.

As your body switches over, it might take a little time for your energy levels to stabilize. During this adjustment period, your body may also have a lower level of electrolytes, which contributes to some of the flu-like symptoms.

Tip: Be sure to replenish your electrolytes by consuming foods rich in potassium, magnesium, and sodium. Consider adding salt to your meals, drinking bone broth, or taking electrolyte supplements.

Fun Fact: Studies show that about 20-30% of people on a ketogenic diet experience some form of keto flu, but the symptoms usually subside after a few days to a week as the body adapts.

5. Weight Loss

Weight loss is another indicator that you might be in ketosis, though it’s not always immediate. Early on, much of the weight loss may be attributed to the body losing water weight, as mentioned earlier.

However, once you’re in ketosis, your body begins to burn fat as its primary fuel source, which can lead to more sustainable weight loss over time.

On average, people who follow a strict ketogenic diet can lose anywhere between 1-3 pounds per week, especially during the initial stages. However, weight loss varies from person to person depending on factors like metabolic rate, activity level, and adherence to the diet.

Tip: Track your weight loss progress over several weeks to get an accurate picture. Don’t rely on daily fluctuations!

6. Improved Mental Clarity and Focus

Another sign that you might be in ketosis is improved mental clarity. Many people report experiencing sharper focus, better concentration, and even increased energy levels once they’ve adjusted to the ketogenic diet.

This is likely due to the ketones being an excellent source of fuel for the brain, which may explain the enhanced cognitive function. In fact, studies have shown that ketones can provide a more efficient and stable source of energy for the brain than glucose.

Fun Fact: Research published in Neurochemical Research showed that after just three days of following a ketogenic diet, participants experienced a significant improvement in mental clarity and cognitive performance.

Enjoy the Journey to Ketosis

So, how do you know if you’re in ketosis? It comes down to watching for signs like increased ketones in your breath, blood, or urine, changes in your breath odor, increased thirst, frequent urination, temporary fatigue, and weight loss.

Keep in mind that everyone’s body reacts differently to ketosis, and it might take a little time for some signs to appear.

Whether you’re following a keto diet for weight loss, increased energy, or mental clarity, it’s important to stay patient with the process. If you’re unsure about whether you’re in ketosis, using testing methods like blood or urine strips can help give you a clearer picture.

And remember—there’s no rush! Let your body gradually adjust to this new fuel source, and you’ll start to feel the benefits in no time.