Most Common Side Effects of Ketogenic Diet And Remedies

Written By: Julie Tang, MS, RDN, CNSC

The ketogenic diet, also known as the keto diet, is a high fat, moderate protein, very low carbohydrate eating pattern. It was developed in the 1920s to treat severe epilepsy in infants and children under a physician’s order, which is then typically monitored closely by a registered dietitian. Epilepsy is a neurological disorder that causes recurrent seizures.

Since the discovery of the keto diet, it has been widely used to control seizures with astonishing rates of effectiveness. According to the statistics provided by the Epilepsy Foundation, over half of the children who go on the clinical keto diet have at least a 50% reduction in their number of seizures. Some children, usually 10-15%, even become seizure-free.

Over the years, the keto diet has evolved beyond its use as a clinical treatment. It has risen in popularity in recent years to mainstream audiences and has many people cutting back on carbohydrates and eating a higher fat diet with the hopes of weight loss and health promotion.

Read on to learn what this diet is all about. We’ll review its potential benefits and look at a few of the most common side effects experienced by keto diet users.

What is a keto diet?

A keto diet is very low in carbohydrates, typically 20 to 50 grams per day, and very high in fat, typically 60-75% of total calorie intake. This drastic reduction in carbohydrates causes the body to go into ketosis, which is the burning of fat instead of glucose for fuel. When this happens, the body converts fatty acids into ketones, which are natural chemicals the body produces when you burn fat for energy. Moderate protein intake is recommended while on the keto diet in order to maintain lean body mass.

According to Gomez-Arbelaez et al (2017), an estimated 0.8 g to 1.2 g protein per kilogram of body weight has been correlated to no loss in muscle tissue while on a low carbohydrate diet (to convert body weight from pounds to kilograms, take the weight in pounds and divide by 2.2). Having the right amount of protein on a keto diet is important because excessive protein intake may disrupt the ketosis state by the conversion of protein to glucose through a process called gluconeogenesis.

Is keto healthy?

The keto diet has been widely studied for its benefits on weight loss, health and performance. A number of studies, including randomized control trials by Yancy Jr et al (2004) and Brehm et al (2003) found that a carbohydrate-heavy diet was more effective in weight loss than a low-fat diet, which was traditionally advised in many diet programs. In addition, research subjects reported reduced cravings and hunger while on a very low carbohydrate diet, which may be helpful in portion control and weight management.

Further studies are now looking to understand the potential benefits of the keto diet for individuals with diabetes, prediabetes, and its role in reducing the risk of heart disease, Alzheimer’s, and certain cancers.

While there seem to be several promising outcomes of the keto diet from studies so far, some health experts remain skeptical because many of the studies have shown short-term results. Whether it works in the long term or whether it’s safe to be on the diet for a long period of time remains unclear.

What are the common side effects of a keto diet?

The keto diet is a strict diet, and for many people, switching to a very low carbohydrate diet is a major change. The body enjoys staying in homeostasis and when major metabolic shifts take place, it needs time to adapt to this pattern of eating. The alterations in metabolism often result in side effects experienced by many keto diet users. Most of the time, the side effects are short-term as the body adapts to ketosis, but this may take up to two weeks.

For people going on the keto diet for the first time, it is important to be aware of the potential side effects. Monitoring the side effects and how long they last could be key indicators of whether they need to adjust their keto diet to optimize ketosis or in some cases, if side effects persist, it may be a sign to stop the keto diet altogether to prevent serious health risks.

These are the most common side effects of following a keto diet, along with suggested remedies to address them:

  1. Keto breath – Keto breath is a distinct taste or odor in the mouth that results from the production of ketones. Ketones include beta-hydroxybutyrate, acetoacetate, and acetone. Some people describe keto breath as having a metallic taste. It may also be fruity-smelling or have a strong odor that’s similar to nail polish remover. People may notice a change in their breath within days or a week of starting the diet. Keto breath is temporary and will subside in about two weeks as the body adjusts to lower carbohydrate intake. In the meantime, the best ways to lessen keto breath are to hydrate well with water, practice good oral hygiene and freshen up breath with gum or mint throughout the day. It may also help to slightly increase carbohydrate intake to reduce the number of ketones produced.
  2. Fruity smell in urine – Although not as common as keto breath, urine can have a “fruity” odor to it. The higher the concentration of ketones in the blood, the more odorous the smell is likely to be. In some medical conditions such as urinary tract infection, maple syrup urine disease or diabetic ketoacidosis, in which ketones build up to a dangerously high level, they too, can cause a fruity smell to urine, so be sure to not confuse this with serious medical conditions that require medical attention. It is best to stay aware, monitor and check with a provider if symptoms seem suspicious or persist. There are a few things that may help reduce the odor of the urine. Try reducing protein intake. During the breakdown of protein in the body, ammonia is produced, which is responsible for the pungent smell. By having slightly less protein, there will be less ammonia. In addition, drink a lot of fluids. A very low carbohydrate diet can be dehydrating to the body. The more dehydrated you are, the more concentrated the urine will be and the stronger the odor.
  3. Keto flu The keto flu is a condition that describes a group of symptoms that results when someone is starting the keto diet. It is not actually the flu so it’s not contagious, but it could feel very similar to the flu. The symptoms are often felt within a few days of starting the keto diet. They can last up to a week, or sometimes longer, for some people. Symptoms can be mild, or moderate to severe, and it varies from person to person. People may experience nausea, vomiting, constipation, diarrhea, headache, irritability, muscle soreness, weakness, difficulty sleeping, brain fogginess, poor concentration, and fatigue. During this time, it is important to stay hydrated, replace electrolytes, get adequate sleep, avoid strenuous exercise and seek medical help if symptoms get worse or persist. To avoid the keto flu or lessen the severity of keto flu symptoms, it is recommended to ease into the keto diet. You can do this by consuming the higher end of the recommended carbohydrate intake (20-50 grams) and gradually reduce it to allow your body to transition slowly.
  4. Constipation – Many people on low carbohydrate diets experience constipation when they first make the change, but it usually gets better over time. Constipation is generally described as having fewer than three bowel movements per week. The reduced fiber intake from carbohydrate restriction and dehydration are common causes of keto constipation. The recommended amount of dietary fiber is 25-35 grams per day for a healthy adult. If a person is just starting on a keto diet, they may experience constipation for a few days, but it can last for a few weeks. If constipation persists longer than 2-3 weeks, it is best to address it with a doctor. Untreated long-term constipation can lead to problems such as anal fissures, hemorrhoids, and abdominal pain. To address keto constipation, drink plenty of water and avoid fluids that may cause dehydration, including excess alcohol and caffeinated beverages. Be sure to incorporate fiber-rich foods such as leafy greens, berries, nuts, and seeds to the diet. You may also consider a fiber supplement. In addition, staying active with exercise can help relieve constipation.


1. Brehm, B.J., Seeley, R.J., Daniels, S.R. & D’Alessio, D.A. A Randomized Trial Comparing a Very Low Carbohydrate Diet and a Calorie-Restricted Low Fat Diet on Body Weight and Cardiovascular Risk Factors in Healthy Women. The Journal of Clinical Endocrinology & Metabolism, 2003 Apr 1;88(4):1617–1623.

2. Gomez-Arbelaez, D., Bellido, D., Castro, A., Ordoñez-Mayan, L., Carreira, J., Galban, C., Martinez-Olmos, M., Crujeiras, A., Sajoux, I. & Casanueva, F. Body Composition Changes After Very-Low-Calorie Ketogenic Diet in Obesity Evaluated by 3 Standardized Methods. J Clin Endocrinol Metab. 2017 Feb 1;102(2):488-498.

3. Yancy Jr, W.S., Olsen, M.K., Guyton, J.R., Bakst, R.P. & Westman, E.C. A Low-Carbohydrate, Ketogenic Diet Versus a Low-Fat Diet to Treat Obesity and Hyperlipidemia: A Randomized, Controlled Trial. Ann Intern Med. 2004 May 18;140(10):769-77.

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