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Possible Side Effects of a Keto Diet

Written by Sioned Bryant

Side Effects of a Keto Diet

What is the ketogenic diet?

The ketogenic (or keto) diet is a low carbohydrate and high fat (LCHF) diet. Adherence to the ketogenic diet aims to push the body into a state of ketosis (which is similar to what happens in starvation) where it uses fat instead of carbohydrates as an energy source (1). The keto diet requires carbohydrates to be restricted to a very low amount of 20-50g per day in order to make glucose reserves insufficient. When there are insufficient glucose stores, the body breaks down fats to produce fatty acids. However, our brain cannot use fatty acids as a source of energy, so ketone bodies called acetoacetate and beta-hydroxybutyrate are produced in the liver as an alternative fuel source (2).

Carbohydrates are the brain and body's preferred energy source so our body needs to work really hard to ensure our brain receives adequate energy if there isn’t enough carbohydrates in our diet.

What can you eat on a ketogenic diet?

The ketogenic diet is a LCHF which is very restrictive. Foods that need to be avoided are:

  • Pasta, grains and bread

  • Beans and pulses

  • Fruit

  • Dairy (milk, yoghurt etc)

  • Sugar-containing drinks (e.g. soft drinks, juice and alcohol)

  • Vegetables containing higher volumes of carbohydrate such as pumpkin and potatoes

You might be wondering what foods are left to eat! On a keto diet you can eat eggs, fish, meat, butter and oils, avocado, nuts and low carbohydrate vegetables.

When is the keto diet recommended?

The ketogenic diet is not a new way of eating. It was developed in the 1920’s as an alternative treatment for epilepsy (3). Originally, epileptic seizures were treated by long fasting periods and medication, however, due to this being unsustainable and with low adherence rates, the ketogenic diet was developed as a more manageable alternative with similar effects as fasting.

The pathways involved in the ketogenic diet for epilepsy management are still unclear. One hypothesis is that glucose metabolism provides rapid and readily available energy for seizure activity (4). So by reducing carbohydrate intake, glucose energy levels are low, and the brain converts to using ketone bodies as an energy source which reduces the frequency of seizures.

Beyond epilepsy, the ketogenic diet is now being trialed in weight management, management of Type 2 Diabetes, Autism Spectrum Disorder, Parkinson’s Disease and Alzheimer’s Disease (5). The research to support it’s use in these areas is still new and inconclusive.

What are the potential side effects of a keto diet?

There are many physical and psychological side effects associated with following the ketogenic diet.

Physical side effects:

  • Short-term side effects or 'keto flu’ such as fatigue, headaches, dizziness, nausea, vomiting, constipation and low exercise tolerance.

  • Long-term medical complications such as hepatic steatosis (fatty liver) and kidney stones

  • Vitamin deficiencies - when you eliminate fruit, vegetables and grains from your diet you risk developing deficiencies in micronutrients such as selenium, magnesium, phosphorus, and vitamins B and C (6). Any diet which eliminates food groups, including a vegan diet, needs to be mindful of potential deficiencies.

  • Poor gut health due to inadequate fibre intake. Fibre is typically obtained through a diet rich in wholegrains, fruit and vegetables. Fibre is not only essential for digestive help but also has been linked to lower risk of heart disease, type 2 diabetes, and bowel cancer.

Psychological side effects:

  • Development of disordered eating

  • Social isolation and avoiding social events where food is involved

  • Anxiety and low mood

Why is there so much hype about going keto?

The ketogenic diet has gained popularity in recent years, mostly in the dieting world as a "quick-fix" weight loss strategy and athletes for increased performance. There is some evidence that suggests that a LCHF diet can result in improved sporting performance (8,9), however, evidence for the long term impact on health and performance is limited. We also need to acknowledge that the keto diet has been pushed in the media and extreme diets sell so it has been a popular choice and promoted by celebrities and influencers. Unfortunately, sensible balanced eating doesn’t make the headlines.

Is a keto diet suitable if I have or have had an eating disorder?

There is no evidence to suggest that the ketogenic diet can cause an eating disorder. However, dieting in general is a major predictor of developing an eating disorder. The keto diet is restrictive and results in physical and psychological side effects which can increase obsessive thoughts around food, fixation on body shape and weight, and rigid food rules. Feelings of failure can also be present when restrictive diets aren't maintained (7).

Following a keto diet can damage a person’s relationship with food, increasing fear of eating carbohydrates and should not be recommended for anyone who is in recovery from an eating disorder or has a history of one.

At the end of the day, the ketogenic diet is highly restrictive and is not sustainable for most people. In the long-run, immune function can be compromised, and there is evidence that the ketogenic diet is associated with micronutrient deficiencies and compromised cardiovascular health, all of which results in an increased mortality (10). Eating a well-balanced plate wins every time for the majority however, we are all unique so make sure you do what is best for you.

At the TC Nutrition clinic we can support you to find a way of eating which is balanced, free from restrictive food rules and tailored to you. Get in touch for a free 15 minute discovery call to see how our specialist dietitians can support you on your journey to food freedom.

Sioned Bryant

Guest Contributor

Follow Sioned on Instagram @life_of_bry-_



1. Giroux NF. The keto diet and long-term weight loss: Is it a safe option? Inquiries Journal [Internet]. 2020 [cited 2021 Apr 15];12(10). Available from:

2.Panov A, Orynbayeva Z, Vavilin V, Lyakhovich V. Fatty acids in energy metabolism of the central nervous system. Biomed Res Int. 2014;2014:472459.

3.Ułamek-Kozioł M, Czuczwar SJ, Januszewski S, Pluta R. Ketogenic diet and epilepsy. Nutrients. 2019;11(10):2510.

4.D’Andrea Meira I, Romão TT, Pires do Prado HJ, Krüger LT, Pires MEP, da Conceição PO. Ketogenic Diet and epilepsy: What we know so far. Front Neurosci. 2019;13:5.

5.Paoli A, Rubini A, Volek JS, Grimaldi KA. Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. Eur J Clin Nutr. 2013;67(8):789–96.

6.Batch JT, Lamsal SP, Adkins M, Sultan S, Ramirez MN. Advantages and disadvantages of the ketogenic diet: A review article. Cureus. 2020;12(8):e9639.

7.Can the keto diet cause an eating disorder? [Internet]. 2019 [cited 2021 Apr 15]. Available from:

8.Stellingwerff T, Spriet LL, Watt MJ, Kimber NE, Hargreaves M, Hawley JA, et al. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. Am J Physiol Endocrinol Metab. 2006;290(2):E380-8.

9.Shilpa J, Mohan V. Ketogenic diets: Boon or bane? Indian J Med Res. 2018;148(3):251–3.

10.Kirkpatrick CF, Bolick JP, Kris-Etherton PM, Sikand G, Aspry KE, Soffer DE, et al. Review of current evidence and clinical recommendations on the effects of low-carbohydrate and very-low-carbohydrate (including ketogenic) diets for the management of body weight and other cardiometabolic risk factors: A scientific statement from the National Lipid Association Nutrition and Lifestyle Task Force. J Clin Lipidol. 2019;13(5):689-711.e1.


Talia Cecchele Nutrition is a team of registered dietitians specialising in eating disorders, disordered eating, digestive issues and sports nutrition. We aim to bring balance back to nutrition, help you to break free from food rules and find food freedom. We offer virtual consultations and group programs so whether you are based in London, the United Kingdom or around the world we would love to support you. To enquire about private consultation please fill out a contact form.



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