The Side Effects of a Ketogenic Diet

Many people are wary of starting a ketogenic diet because they have long heard the American Medical Association promote five fruits and vegetables per day. They have heard that fiber is touted for its ability to keep us regular. Fat was painted as an enemy to personal health during the 1980s. Therefore, before starting the diet, people want to know what are the side effects of a ketogenic diet going to be? What impact will the ketogenic diet have on your health?

I personally was reluctant to adopt the ketogenic diet despite having epilepsy for many years. My neurologist dismissed it as a treatment when the first line of anticonvulsants produced moderate results. However, as the years went by, the side effects of lamictal, keppra, depakote and tegretol took their toll on me. Eventually, I started experimenting with diets. Although, I started with a more popular raw vegan diet and tested out the AutoImmune Paleo diet, the GAPs diet and finally decided to go all in with the ketogenic diet when my chiropractor was recommending it. I’m glad I did! I’m completely off anticonvulsants now and enjoying much higher levels of energy.

The Most Common Side Effects

When restricting carbohydrates, the most common side effects include:

  • Bad Breath
  • Headaches
  • Weakness
  • Fatigue
  • Diarrhea or Constipation

It is important to note that most of these side effects subside after the first few weeks. The studies that put obese patients on a ketogenic diet for 6 to 2 years demonstrated that the subjects had no side effects or complications. Marathon runners, cyclists and Ironman competitors who were on the ketogenic diet for up to 3 years reported no side effects either.

Athletes reported that the ketogenic diet actually improved their performance and helped them burn more fat for fuel than when they were on a high-carbohydrate diet.

When the ketogenic diet is used to treat epilepsy in children, it rarely leads to serious complications. Research suggests that they should supplement with magnesium, zinc, vitamin D, and vitamin B. It is also suggested that children take trace minerals after two years on the ketogenic diet.
While major side effects are rare on the ketogenic diet, even after an extended period, it is important to understand what happens during ketosis and how it impacts the body. This can help to prevent or relieve almost all potential side effects and help people feel better on a low carbohydrate diet.

What Happens When You Restrict Carbohydrates

At the onset of the ketogenic diet, your body will be searching for more sugar to burn for fuel. You may even find yourself craving carbohydrates for the first few days. When the glucose from foods is exhausted, your body must adapt and start to use fat. Your blood sugar levels will decrease and your body will increase its levels of cortisol. Cortisol is a glucocorticoid hormone that your adrenal glands release to make sure you have enough energy to survive. Low blood sugar levels signal to the brain’s adrenal glands that cortisol should be released. This stimulates a process called gluconeogenesis. Gluconeogensis converts protein into sugar.

In time, the body will adjust and start burning fat for fuel instead of protein. This is the process known as ketosis. It is the body’s way of preserving glycogen and muscle mass during times of starvation or carbohydrate restriction. Ketosis does not happen immediately. It may take a few days or even a couple weeks before your body enters ketosis. This can leave you feeling fatigued, weak and even a bit stressed in the mean time.

While increasing cortisol isn’t a good thing, the increase that happens on the ketogenic diet is insignificant when compared and contrasted to the cortisol levels of people who consume high and moderately high carbohydrate diets. I

One main concern for people looking into the ketogenic diet is the ammonia that is produced as a by-product when protein is used for fuel. The ketogenic diet limits the amount of protein consumption to a moderate level. The body is mainly burning fat for fuel. Therefore, studies that were done on patients on the ketogenic diet showed no evidence of kidney damage.

Mineral levels will fluctuate on the ketogenic diet. When cortisol gets released as a response to the carbohydrate restriction, it prevents cells from releasing sodium and accelerates the rate of potassium secretion. This may lead to fatigue, constipation, and weakness. The cortisol increase is not the only factor that is responsible for the fluid and mineral loss noticed by a low carbohydrate diet.

Loss of Minerals on the Ketogenic Diet

As you transition to a much lower carbohydrate level, the body wants to eliminate more waste. This creates a diuretic effect and flushes out some minerals. This is why many people who are on ketogenic diets are concerned about ensuring that they are getting their electrolytes.

Additionally, less insulin can lead to less sodium. Insulin is a hormone that decreases our blood sugar when it is too high. The main job of insulin is to move sugar into cells so that they can use it as fuel and store the excess sugar as fat. Insulin will also act on the kidneys to promote sodium readsorption.

Therefore, when people restrict carbohydrates, insulin levels tend to be reduced as well. This is one of the reasons why low-carbohydrate diets are beneficial for people with diabetes and obesity. However, it is another reason why low-carbohydrates have a diuretic effect. Low levels of insulin lead to reduced sodium re absorption.

Sodium then draws more fluid into the kidneys to be ready for excretion.

If you experience symptoms like headaches, nausea, confusion and fatigue that doesn’t go away, it is important to increase your sodium levels. You can do this through unrefined salt and water intake. Many people also drink pickle juice to replace the sodium and minerals lost.

The sodium will then be able to draw more fluid to the kidneys for excretion. If you are seasoning your foods with salt, this is unlikely to lead to low levels of sodium.

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Muscle cramps occur due to a loss of minerals. This frequently happens when you first start the ketogenic diet. Drinking lots of water and eating salt can prevent this common side effect. Many drink pickle juice to combat this side effect. If you feel that a supplement would be better, you can look into taking three slow release magnesium tablets each day for 20 days. After that reduce it to one tablet each day. This is recommendation from Dr. Jeff Volek and Stephen Phinney.

Stinky Breath on a Ketogenic Diet

One uncomfortable side effect of a ketogenic diet is bad breath. Once you achieve that goal of burning fat for fuel, your body produces acetone, which is the main cause of bad breath on a ketogenic diet.

Acetone is one of the by-products of ketosis. It can leak out of your breath and sweat when you are first entering ketosis. The degree of smell will depend on how your body handles the by-products of ketosis.
While I personally, have never experienced bad breath on ketosis, many people do. It can take a few weeks to go away. It is best to simply mask it with herbal mint sprays and sugar free gums, adequate fluid and salt intake and good oral hygiene.

Tips to Avoid the Side Effects of a Ketogenic Diet

It is the transition in and out of ketosis that tends to trigger these side effects. Therefore, you will want to avoid too much in and out transition. Many of these side effects can be remedied by the following steps:

  • increase water intake
  • increasing your salt intake
  • ensure fat levels are high enough

If you discover that you are still struggling with the symptoms, adjust your level of carbohydrates. Test out a slightly higher level of carbohydrates and slowly decrease to a lower level. Listen to your body and keep track of how you feel on the different levels of carbohydrates. Don’t stress out about it too much. You’ll get to a fat-burning body in no time!


While there are some side effects to the ketogenc diet, the benefits of the ketogenic diet far outweighs the side effects. The side effects tend to go away over time, while in the long run, the ketogenic diet can help stabilize your weight, stabilize your mood, protect your brain health and even prevent Alzheimer’s. It is well worth your time to check out the ketogenic diet and incorporate it into your life, especially if you are suffering from epilepsy!



2 thoughts on “The Side Effects of a Ketogenic Diet”

  1. Hiya Melinda. This is brilliant and something now I’m looking more into. I didn’t know that much about it until you explained it particularly well which you gave me a great understanding and insight. I’m currently overweight so I’m definitely trying this out. I bookmark this site and keep tabs on new posts, thanks for highlighting this and sharing it.

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