Is Ketosis Safe? Short Term and Long Term Side Effects of Ketosis

Nutritious meal on plate with the heading IS KETOSIS SAFE? above the plate.

Is Ketosis Safe? Short-term and Long-term Effects of Ketosis - Dr Avi Charlton

Nutritious meal on plate with the heading IS KETOSIS SAFE? above the plate.

As a doctor who promotes keto and low-carb diets, I get a lot of patients wanting to see me for opinions on this diet:

  • Is ketosis safe?
  • Is ketosis dangerous?
  • What are some ketosis diet side effects?

Often they are told it’s dangerous. The safety of the keto diet is often controversial in the medical community. We often understand it works for weight loss. However, critics claim it can be non-sustainable or dangerous due to the diet’s high-fat or high protein content. Sometimes cholesterol levels can be raised which raises alarm to the treating doctor. In my experience, this is often due to the lack of understanding of the mechanisms of ketosis and the ketogenic diet.

What is Ketosis? 

Ketosis is a metabolic state in which the body uses fat and ketones to produce energy rather than glucose. If a person mainly eats the standard American diet, consisting of a high proportion of carbohydrates, the body will rely on glucose as its primary fuel. However, if carbohydrate intake is very low, the body can learn and adapt to switch its fuel source to rely on fat. The liver will produce ketones, or ketone bodies, which are fat-like compounds that your brain and organ can utilize energy with instead of glucose.


We can measure ketone levels with various methods, including urine, blood, or breath ketones. I recommend blood ketones as a more reliable method of measuring ketones. According to Dr Steve Phinney and Dr Jeff Volek, nutritional ketosis is defined as blood ketone levels of 0.5-3mg/dL.(1) 


Is Ketosis Safe? Is Ketosis Dangerous?

Nutritional ketosis and diabetic ketoacidosis are different:

The safety and concern of ketosis are often confused with the term ketoacidosis. Nutritional ketosis and diabetic ketoacidosis are different.

Diabetic ketoacidosis happens in individuals with type 1 diabetes. Their blood ketones and glucose rise to dangerous levels due to blood insulin levels going too low, creating too much acid in the body. In such instances, it is an emergency and diabetics need to be given insulin as well as fluid replacement to correct the acid-base balance of the body. 

In nutritional ketosis,  the body’s acid-base homeostasis is maintained. The body adapts to utilizing ketone bodies as the predominant fuel.


How Long Can You Stay in Ketosis Safely?

Side by side list of the effects carbs and fat have on the body's fuel source.

Ketosis is a nutritional state in that we switch from using glucose as fuel to using ketones as fuel. It is perfectly safe as a long-term fuel. In fact, this is a cleaner fuel system with less risk of inflammation and doesn’t rely on glycogen stores. We can also access the body’s stored fat this way and convert this fat as fuel. 

Is Ketosis Dangerous Long-Term?

The ketogenic diet has been used to treat epilepsy for decades before epileptic medications were invented.(2) In 2021 it was precisely 100 years from when the ketogenic diet was first described in the medical literature to treat epilepsy. The ketogenic diet has been a safe and effective treatment for this group of patients. (


Concerns That Have Come up About the Long-Term Safety of Ketogenic Diets Include:

List of myths about the keto diet with answers to the myths right below them.

  1. Increased risk of cardiovascular disease, due to the high fat intake
  2. Ketogenic diets are lacking in nutrients, including fiber, micronutrients, and vitamins.
  3. Ketogenic diets increase inflammation
  4. Too much protein will harm your kidneys

Concerns About the Increased Risk of Cardiovascular Disease

Because the ketogenic diet often has a high saturated fat percentage, there has been a fear amongst the medical and general community that the ketogenic diet will raise cholesterol and increase the risk of cardiovascular disease (CVD). There is now growing evidence, cited by > 20 review papers, that concluded that saturated fats have no increased risk of CVD. The diet-heart hypothesis, introduced in the 1950s, was based on weak, associational evidence.(3) in 2020, The American College of Cardiology published an article saying there is no evidence to limit the intake of saturated fat. The article goes on to discuss that increased intake of saturated fat can increase low-density lipoprotein (LDL) numbers in the cholesterol profile but it does not increase the number of small, dense LDL particles, but rather the larger LDL particles.(4) The small dense LDL particles are associated with an increased risk of metabolic syndrome and atherosclerosis.(5) The general medical community has not taken a full grasp of the concept of different sizes of LDLs as yet. 

Contrary to what has been believed, we are now understanding that there is a lack of correlation between dietary cholesterol and blood cholesterol.(6)  There are also further studies indicating that dietary cholesterol does not increase the risk of CVD.(7) For example, some studies look at how many eggs people eat and their cholesterol. They have found no association that eating more eggs increases blood cholesterol.(8,9,10)

Contrary to the concern, there is a study showing nutritional ketosis reduces CVD risk. They measured biomarkers, including small dense LDL, triglyceride/HDL ratio, blood pressure, CRP, etc. The majority of studies show ketogenic diets lead to a reduction in triglyceride, an increase in high-density lipoprotein (HDL), and an increase in the size of LDL particles. Ultimately, this results in a reduction in CVD risk. The conclusion was the 10-year score for CVD is reduced in the nutritional ketosis group.(11)


Concerns About the Ketogenic Diet Lacking in Nutrients

Critics of ketogenic diets often have concerns about nutrient deficiencies. However, any diet can be deficient in nutrients. 

Iron deficiency is the most common nutrient deficiency in the world, affecting more than 25% of the population worldwide.(12) Zinc deficiency is also very common in the world. (13). Other common deficiencies include iodine, Vitamin D, Vitamin B12, calcium, vitamin A, and magnesium. Most of the above nutrients are found in animal-based diets. Vegan and vegetarian diets have an increased risk of nutrient deficiencies, especially vitamin B12, fat-soluble vitamins including A, D, E, K, and zinc.

This paper reviewed 10 studies and concluded that carbohydrate-restricted diets do not consistently cause nutrient deficiencies.(14)

Caryn Zinn and Amy Rush belong to a group of dieticians, who wrote an article demonstrating how LCHF (low carb high fat) meal plans are able to meet micronutrient requirements, even though their macronutrients ratios do not align with current dietary guidelines.(15) There is an increasing request to review the dietary guidelines by various academics.


Concerns About Ketogenic Diets Being Inflammatory

In a study conducted by Dr. Steve Phinney, he and his colleagues measured several markers of inflammation. A very low carbohydrate diet resulted in a profound reduction in inflammation compared to a low-fat diet.(16)


Concerns About Too Much Protein Harming Your Kidneys

Some critics have described ketogenic diets are too high in protein and may cause kidney damage.

I have examined 2 systematic reviews,(17, 18) both of these studies do not support any adverse effect of increased protein intake on kidney function or blood pressure in healthy adults. In fact, ketogenic diets can improve the control of diabetes and improve markers of metabolic syndrome and subsequently improve kidney functions.


Concerns About Bone Health

There have been concerns about the ketogenic diet increasing bone turnover. This study compared subjects to controls and measured their bone turnover markers (N-telopeptide). After 3 months, there was no significant change in bone turnover compared to controls.(19) The following study also supports high-protein diets helping to preserve bone health.(20)


Possible Ketosis Diet Side Effects

When a person first drastically reduces their carbohydrate intake, the body will change the fuel system from burning glucose to burning ketones. Sometimes symptoms may occur including:

  • Headaches
  • Fatigue
  • Brain fog
  • Nausea
  • Poor physical performance
  • Constipation
  • Difficulty sleeping
  • Muscle cramps

These symptoms typically get worse from day 4 and can last up to 2 weeks. Sometimes the breath and urine can smell like acetone. 

These symptoms are caused by a combination of dehydration and electrolyte imbalance. When blood glucose is drastically reduced, the blood insulin level also drops, which flushes out sodium in the urine. Other electrolytes, including magnesium and potassium, can also be lost during this period. 

A real food diet often has much less salt content than a processed food diet. Hence a drop in dietary salt intake.


How to Minimize Ketosis Side Effects

electrolyte illustration of woman drinking water and 4 tips pointing away from her explaining what you should be consuming daily apart from water to balance electrolytes for keto diet.

These side effects can be minimized by increasing salt intake. I would recommend a daily intake of 2000-4000mg per day. Most health authorities currently recommend limiting salt intake to around 2300gm of sodium a day, but I am unsure what science this is based on. People eating a low-carb or ketogenic diet often have an increased need for salt. They do not eat processed foods, which generally have higher salt content. There is also increased urinary excretion of salt when insulin is reduced.

Hence, It is important to maintain good hydration with fluids such as water, electrolytes, bone broth, tea, mineral water, or pickle juice.
Learn more about combatting these side effects

Conclusion | Is Ketosis Safe?

  • Ketosis and ketogenic diets are safe long-term.
  • Nutritional ketosis and ketoacidosis are totally different.
  • There is no evidence that ketogenic diets increase cardiovascular risks, inflammation, kidney disease, or affect bone health.
  • Keto flu can cause troublesome symptoms due to a shift in insulin and electrolytes, which usually settles in 2 weeks.
  • Keto flu symptoms can be minimized by maintaining hydration and mineral intake.

 Interested in learning the connection between the Keto Diet and Electrolytes? Click here to find out:


  1. Volek JS & Phinney SD The Art and Science of Low Carbohydrate Living


This article does not provide treatment or individualised advice. Please discuss with your doctor about your change in lifestyle especially for those who take regular medications or have medical conditions.

I am Dr Avi Charlton. I am a General Practitioner with a special interest in nutrition. I have done training with Nutrition Network and Low Carb Down Under.

Follow me on Facebook or Instagram @dr_charlton_low_carb_GP and @Melbourne Low Carb Clinic.

This page was originally written on 25 April 2023 and published on my website.