Sarah Cimperman, ND

The ketogenic diet is trending, but it’s not new. Doctors have been using it for nearly a century as a treatment for epilepsy and in children it can be more effective than medication.1 Now it’s gaining popularity as a weight loss strategy and a treatment for conditions like type two diabetes,2 cardiovascular disease,2 Alzheimer’s disease,3 polycystic ovarian syndrome,2 and the most common kind of brain cancer.4 While the ketogenic diet has big benefits for some individuals, it’s not right for everyone. Read on to learn more about the diet, the side effects, and the top five reasons that it may not be right for you.

Keto 101

The ketogenic diet is named after ketosis. When the body is running low on fuel, it uses ketosis to produce ketone bodies from fat stores as an alternate source of energy. This only happens when blood sugar levels are low and amino acids from protein have been depleted. Ketosis is not the same as ketoacidosis, a life-threatening complication of diabetes resulting from inadequate levels of insulin. Unlike ketosis, ketoacidosis is characterized by extremely high levels of blood sugar and ketone bodies that alter the pH of the blood, making it too acidic.

The ketogenic diet is a low-carbohydrate and low-protein diet. Unlike other low-carb diets, most calories on the ketogenic diet come from fat. The production of ketone bodies depends on multiple factors including body mass index (BMI), body fat percentage, and resting metabolic rate. The exact amounts dietary fat, protein, and carbohydrates necessary to induce ketosis can vary from individual to individual, but ketogenic diets usually contain 60 to 80 percent fat, 15 to 30 percent protein, and 5 to 10 percent carbohydrates.

The ketogenic diet is based largely on foods like avocados, nuts and seeds, olives, healthy oils (such as extra virgin olive and coconut oils), coconut milk, non-toxic fatty fish (like sardines and wild Alaskan salmon), butter, cream, cheese, eggs, meat, and low-carb vegetables like salad greens, cucumbers, cauliflower, zucchini, eggplant, cabbage, asparagus, tomatoes, peppers, and onions. Foods that are not allowed on the ketogenic diet include sweet foods and beverages, flour-based foods (like breads and pasta), grains (including rice), starchy vegetables (such as potatoes and carrots), legumes (beans and lentils), fruit (except small portions of berries), refined vegetable oils, shortening, margarine, low-fat and fat-free products, and sugar-free diet foods.

Side Effects

It can take time for the body to fully adapt to the ketogenic diet. As this happens, changes in hormones and electrolytes can cause fatigue, headaches, and gastrointestinal upset. Because these symptoms resemble those of the flu, this period is often referred to as “keto flu.” (The ketogenic diet does not cause influenza.) It make take a few days or a few weeks, but signs that the body is in ketosis include dry mouth, bad breath, a metallic taste in the mouth, increased thirst and urination, cold hands and feet, and difficulty sleeping.

There is concern that people who follow the ketogenic diet long-term may experience liver problems, kidney stones, reductions in bone mineral density, nutritional deficiencies, constipation, mood swings, and the lack of mental clarity referred to as “brain fog.” People following the ketogenic diet should work closely with a doctor who can monitor liver and kidney function, test for deficiencies, recommend supplements to replace electrolytes and minimize adverse effects, and make any necessary changes in prescription medications.

Top 5 Reasons to Avoid the Ketogenic Diet

Ketosis is generally considered safe, although most studies have followed people for up to two years and longer term studies are lacking. The ketogenic diet shows great promise as a tool to help prevent and reverse some of the most deadly chronic diseases in the United States, but it’s not a good choice for every individual. Here are the top five reasons to avoid the ketogenic diet.

#1 | You are pregnant or trying to become pregnant.

The ketogenic diet should not be used during pregnancy. Women trying to become pregnant should also stay away from this diet because ketosis is perceived by the body as a state of starvation which makes conception much less likely.

#2 | You have a medical contraindication.

The ketogenic diet may be dangerous for people with liver or kidney problems, pancreatitis, gall bladder disease, disorders of fat metabolism, porphyrias, and deficiencies of certain enzymes like carnitine and pyruvate kinase.

#3 | You have recently lost more than ten percent of your body weight.

People often lose weight on the ketogenic diet, but it’s not always a good thing. If you have recently lost a significant amount of weight—ten percent or more—for any reason, you should avoid the ketogenic diet and consider one that is less restrictive.

#4 | You have an eating disorder.

Restrictive diets like the ketogenic diet should be avoided by people who are struggling with an eating disorder or have done so in the past. These people should work with a doctor who specializes in nutrition to find a less restrictive diet that will meet their needs.

#5 | You love carbohydrates.

Because the ketogenic diet is so restrictive, people who are used to eating more than small amounts of carbohydrates can find it difficult to follow. People who are unable to stop eating sweets and/or starches will not be successful, so these individuals should consider less restrictive low-carb diets.


1 Hartman AL and Vining EP. Clinical aspects of the ketogenic diet. Epilepsia. 2007;48(1):31-42.

2 Gupta L, Khandelwal D, Kalra S, Gupta P, Dutta D, and Aggarwal S. Ketogenic diet in endocrine disorders: Current perspectives. Journal of Postgraduate Medicine. 2017;63(4):242–251.

3 Henderson ST, Vogel JL, Barr LJ, Garvin F, Jones JJ, and Costantini LC. Study of the ketogenic agent AC-1202 in mild to moderate Alzheimer’s disease: a randomized, double-blind, placebo-controlled, multicenter trial. Nutrition & Metabolism (London). 2009;6:31.

4McDonald TJW and Cervenka MC. The Expanding Role of Ketogenic Diets in Adult Neurological Disorders. Brain Sciences. 2018;8(8):148.

SarahCimpermanND_resisedSarah Cimperman, ND is the author of the new book, The Prediabetes Detox: A Whole-Body Program to Balance Your Blood Sugar, Increase Energy, and Reduce Sugar Cravings. She graduated from NCNM in 2002 and has a private practice in New York City. Her expertise has been featured on Fox News and Huffington Post and in Natural Health magazineWhole Living magazine, and the Well Being Journal, among other publications. Dr. Cimperman also writes two blogs, A Different Kind Of Doctor and The Naturopathic Gourmet.

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