How To Know If You Are In Ketosis? (And Potential Side Effects of Keto)

This is Part 3 of 3 in my KETO SERIES, if you want to read the previous parts, you can use the links below to read them first and then come back here.

Here is the link to Part 1: What's Keto? And Does It Really Work?

Here is the link to Part 2: How To Start A Keto Diet


Part 3 of 3: How To Know If You Are In Ketosis? And Potential Side Effects Of The Ketogenic Diet

The keto diet is a diet that requires a low-carb intake, moderate intake of protein and a high amount of fats. When the body "figures out" that there are not enough carbs to use for energy, the burning of fats starts and the process of keto-adaptation begins.

You cut back on carbs, kept the protein intake in moderate amounts and are eating healthy fats.

You stayed clear from "bad keto" foods and followed all the guidelines.

But you are still not sure if you are in ketosis, and that is why I wanted to write this post (to help you find the signs and symptoms of ketosis) and guide you through some common keto problems you might be facing.

It can take up to a few weeks to get through the initial adaptation phase, depending on your body's ability to adapt to burning fat as energy.

From the 30,000 foot overview... if you find yourself having longer-lasting energy, better focus, and your appetite is not what it used to be (you don't feel as bothered - or at least not as often) you are probably in ketosis. But there are more specific things that we can look for in your day-to-day life to tell us if you are currently in ketosis.

Signs that you may be in ketosis:

Keto breath

It's not good for your social life but it can be a positive sign of ketosis. It is actually a (very) common side effect caused by a ketone body called acetone. It makes your breath smell similar to nail polish remover, and some people say it can even smell “fruity.” Sometimes that smell can appear when you are sweating - but more often than not, it is temporary. (1)

Reduced hunger

Many people experience a reduction in hunger on a keto diet, some have reduced appetite even after eating just once or twice a day. (2)

Weight loss

One of the benefits of a keto diet is weight loss, so if you are losing weight it's highly likely that you are in ketosis.

"Keto flu"

Sometimes when you start a ketogenic diet you may experience something nicknamed the “keto flu.” It was given this name because you will have flu-like symptoms and not actually be sick with the flu.

Luckily, it should pass within a week.

Some people report that after a few days of feeling sick and tired (aka the keto flu), they will experience a noticeable increase in energy levels - beyond what they had before starting the keto diet.

(This is mainly based on experiences of people who have tried keto - not medical testing).

More on the "keto flu" later.

Tests you can do to know if you are in ketosis:

For definitive answers, you will need to look at either your blood, urine or breath (yes that's right, the acetone levels in your breath can tell us if you are in ketosis).

Blood ketone test

This is the most accurate method, but it is not as easy to do at home (personally I don't recommend doing this yourself, but maybe your doctor can give you a referral to have it done by your medical system). The test strips can be relatively expensive, especially if you need to test on a regular basis. (5)

Urinary ketone test

Another very common test with the advantage that it can be done at home.

Results of one study suggest that urine testing for ketosis in adults is best done two times per day, start with early in the morning and then again several hours after dinner/ late in the evening. (4)

Urine testing is less accurate than breath or blood tests. However, this kind of testing can be great if you just want a rough idea of the level of ketosis you are currently in. (5)

Breath ketone test

Acetone (what we are looking for) can be measured in the breath. Breath acetone levels have been shown to be a significant predictor of blood ketones. (3) That is what makes them better than the urine test strips but not as accurate as blood tests.

It may be good to invest in one because if you do buy a breathalyzer, you can then test your ketone levels as often as you wish. (5) Making this the easiest choice to keep yourself on track.

Being in ketosis may be a great thing to many people because that means that they are feeling the benefits and that their diet is working, but there are also several harmful effects of ketogenic diets including muscle cramps, bad breath, changes in bowel habits, keto-flu and loss of energy. (6)

The causes of negative side-effects of the keto diet could be:

Too much protein

Low energy after a few weeks or longer, when you should be through with the initial adaptation phase can be a sign of too much protein in your diet.

It can be hard to determine the exact amount that you need. Everyone has their own needs in terms of protein-intake levels, so a small woman will need less protein to feel good than a tall man (their bodies have different hormones and react differently than ours). Therefore protein intake should be adjusted individually. (7)

Not enough minerals and/or water

If you are feeling muscle cramps, constipation, or lightheaded... you might be low on essential minerals or water.

Both minerals and water are important for us because they are required for effective circulation, good muscle function and heart health.

Important minerals to monitor while on keto:

Sodium (salt)

If you don't have enough sodium (salt) in your diet you can have symptoms like lightheadedness, dizziness, and fatigue when exercising (and sometimes constipation- that can be a side effect of not having enough salt and fiber).

When you are in nutritional ketosis your kidneys get more efficient at getting rid of salt so you need to provide it on a daily basis so you can maintain your well-being with this type of lifestyle. (7)


A mineral that is important for heart and muscle function (you can get it from bananas, broth, vegetables, and eating unprocessed meat). (7)


People with diabetes often have a problem with maintaining adequate amounts of magnesium. But this is a mineral that most of us don't get enough of. A major sign of magnesium deficiency is muscle cramp. (7)


Your level of calcium can be maintained by consuming an adequate amount of vegetables, dairy and cheese (and homemade broth). Calcium is necessary for bones, nerve and muscle function. (7)


Not drinking enough water can lead to dehydration, dry mouth, increased thirst, constipation, etc. Make sure you stay hydrated (you can drink water or unsweetened tea or coffee).


How to Get Over the “Keto Flu”

There are a group of symptoms that may appear in the first two to seven days of starting a keto diet. Some of the symptoms include headache, foggy brain, fatigue, irritability, nausea, difficulty sleeping, and constipation. You can't find this term in medical research journals but you will most certainly find it in thousands of blogs and articles, so it can't be said for sure what exactly happens to our bodies, and why some people feel so bad after this dietary change.

It may be related to the low carb intake or detox factor, or it can be a result of changes in the gut microbiome. Whatever the reason is it can happen to some people, while others may not be affected by it at all. (8)

If you do get affected by keto flu... here are some tips on how to deal with it (8) :

First and foremost, you do NOT need to buy expensive products that some websites sell claiming that they will make you feel better (without backing up those claims).

It's not a real flu, so keep calm - you will not develop a fever and the symptoms can hardly ever make you incapacitated. If you feel very ill, consider visiting your doctor, as something else may be happening.

Drink plenty of water and eat your veggies.

That should start to help you feel better (typically within 1-2 days).

Switching to keto can be a big change

so don't give up if you are committed to a plan. You may feel exhausted for a few days, but at the end of a week, your energy level will most likely return to normal and you may feel even better.

If you ever have questions, or need help/ advice, feel free to reach out to me here (I'm always here to help):

Talk soon,



PS. If you have other topics that you would like me to write about, us the contact link above to send me a quick note!

I want to keep researching and producing content that is useful to you.



1. Kathy Musa-Veloso, Sergei S Likhodii, Stephen C Cunnane, The American Journal of Clinical Nutrition, Volume 76, Issue 1, July 2002
“Breath acetone is a reliable indicator of ketosis in adults consuming ketogenic meals”

2. Gibson AA1, Seimon RV, Lee CM, Ayre J, Franklin J, Markovic TP, Caterson ID, Sainsbury A. The Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders, Sydney Medical School, The University of Sydney, Camperdown, NSW, Australia. “Do ketogenic diets really suppress appetite? A systematic review and meta-analysis.”

3. Carmant L. CHU Sainte-Justine, Division of Neurology, Department of Pediatrics, University of Montreal, Montreal, Quebec, Canada, “Assessing ketosis: approaches and pitfalls.”

4. Paul Urbain and Hartmut Bertz, Department of Medicine I, Section of Clinical Nutrition and Dietetics, Medical Center – University of Freiburg, Hugstetter Str 55, 79106 Freiburg, Germany, “ Monitoring for compliance with a ketogenic diet: what is the best time of day to test for urinary ketosis?”

5., “Measuring ketosis on a ketogenic diet”

6. Joshi Shilpa, Viswanathan Mohan, Mumbai Diet and Health Centre, Mumbai, India, Dr. Mohan's Diabetes Specialities Centre & Madras Diabetes Research Foundation, WHO Collaborating Centre for Noncommunicable Diseases Prevention & Control, IDF Centre of Excellence in Diabetes Care & ICMR Centre for Advanced Research on Diabetes, Chennai 600 086, Tamil Nadu, India, “Ketogenic diets: Boon or bane?”,

7. Dr. Stephen Phinney, Virta Health, “Nutritional Ketosis and Ketogenic Diets”

8. Marcelo Campos, MD, Harvard Health, “What is keto flu?”