Keto Diet and Constipation – Overview
The ketogenic diet is a dieting method consisting of increased fat to carbohydrate ratio, which proportions varying in the range of 50-55% fat products, 30-35% protein products, and 10-15% carbohydrate products.
Its name derives from the increased levels of ketone bodies that it generates as a result of fatty acid metabolism.
It was introduced a century ago with the purpose of treating patients affected with refractory epilepsy. At that time, ketogenic diets were designed to include increased amounts of fat products, including vegetable-derived oils.
The keto diet has shown to decrease seizure recurrence in children with refractory epileptic syndromes and many of its effects on health were observed and studied from that time, including weight loss, improved microbiome diversity, increased satiety after meals, augmented energy levels, and a favorable blood lipid profile. (1, 3, 5, 7-9)
Several studies have also assessed the adverse outcomes associated with the ketogenic diet, conceptualizing a new term for this constellation of signs and symptoms: the “keto-flu”.
The symptoms that people on the keto diet experience include gastrointestinal symptoms, such as nausea, vomiting, and constipation. Dizziness, fatigue, decreased exercise tolerance, and increased risk for developing kidney stones have also been reported.
Nonetheless, the keto-flu usually persists for several days to a few weeks, resolving in most people after that. (1-5, 9, 10)
The keto diet and constipation
Constipation is a common concern among people of different age groups and dietary habits. For decades it has been believed that dietary fiber intake has a positive effect on the improvement of constipation, and as mentioned, the keto diet consists of a decreased amount of carbohydrates, from which group fiber-rich vegetables are included.
Consequently, many studies have assessed the rate of adverse reactions to the keto diet and the possible causes associated with them. Many reports state the manifestation of constipation as an outcome associated with the keto diet, but most of them observed the short-term duration of this symptom.
Another study highlights the increased need for water consumption under the keto diet, a factor presumably related to increased heat production by high-protein diets. (5, 6)
Factors associated with constipation
The colonic mucosa, the inner layer of the large intestine, is the place where most of the water intake is absorbed along with most of the minerals consumed. This is also the place where feces are completely formed because of their desiccation.
Dietary fiber is a vegetable product indigestible by humans and is fermented by colonic bacteria to produce important by-products for their living, that are also used by the human body, such as short-chain fatty acids. Dietary fiber absorbs water along its way in the gastrointestinal tract, augmenting the volume of feces.
Intestinal motility is another factor associated with constipation, since the more time that feces persist in the large intestine, the more dehydration they suffer. This factor has been studied in patients with Parkinson’s Disease, in whom this clinical concern is a very common finding. (11)
The intestinal microbiota and its changes have also been studied, demonstrating that low carbohydrate diets change their composition to a favorable bacteria diversity profile. (10)
Lastly, other factors like concomitant diseases or some groups of medications are also associated with the production of constipation.
The individual approach
As stated by the studies consulted, constipation is a common concern among people with different dietary habits, including the keto diet. Furthermore, one randomized control trial performed by Neal et al. encountered a decreased rate of constipation in children on a low-carbohydrate diet compared to those on a low-fat diet. (7)
These dissimilar results raise the question of the implications of the keto diet in the production of constipation. However, several of the factors implicated in constipation were not thoroughly evaluated.
Furthermore, daily water intake, dietary fiber consumption, intestinal microbiota composition, and the concomitant use of medications known to produce constipation differ on an individual basis.
The latter generates the need for an individualized approach when evaluating constipation, as many of the factors implicated could be present or not.
Therefore, to have a better understanding of the individual risk-benefit relationship associated with the keto diet, consultation with a medical professional specialized in dietary modification is warranted.
A ketogenic diet is a dietary approach that consists of increased fat to carbohydrate ratio. It has been associated with notable health benefits at the time of its study and development.
Numerous adverse reactions associated with the keto diet are mild to moderate and resolve in several days to a few weeks.
Constipation is a common concern not only among people on the keto diet but also among people on conventional diets.
There are many factors associated with the development of constipation including daily water intake, dietary fiber consumption, intestinal microbiota composition, and the concomitant use of medications.
Therefore, if one is about to start the ketogenic diet to benefit from its health outcomes, it is advisable to consult a specialized medical professional to assess the personal factors associated with constipation and other adverse reactions to the ketogenic diet.
1. Kang, H.C., Chung, D.E., Kim, D.W. and Kim, H.D. (2004), Early- and Late-onset Complications of the Ketogenic Diet for Intractable Epilepsy. Epilepsia, 45: 1116-1123.
2. Schmidt, M., Pfetzer, N., Schwab, M. et al. Effects of a ketogenic diet on the quality of life in 16 patients with advanced cancer: A pilot trial. Nutr Metab (Lond) 8, 54 (2011).
3. Elizabeth G Neal, Hannah Chaffe, Ruby H Schwartz, Margaret S Lawson, Nicole Edwards, Geogianna Fitzsimmons, Andrea Whitney, J Helen Cross. The ketogenic diet for the treatment of childhood epilepsy: a randomised controlled trial, The Lancet Neurology, Volume 7, Issue 6, 2008, Pages 500-506.
4. Ruiz Herrero J, Cañedo Villarroya E, González Gutiérrez-Solana L, García Alcolea B, Gómez Fernández B, Puerta Macfarland LA, Pedrón-Giner C. Classic Ketogenic Diet and Modified Atkins Diet in SLC2A1 Positive and Negative Patients with Suspected GLUT1 Deficiency Syndrome: A Single Center Analysis of 18 Cases. Nutrients. 2021; 13(3):840.
5. William S. Yancy, Maren K. Olsen, John R. Guyton, et al; A Low-Carbohydrate, Ketogenic Diet versus a Low-Fat Diet To Treat Obesity and Hyperlipidemia: A Randomized, Controlled Trial. Ann Intern Med.2004;140:769-777.
6. Carol S. Johnston, Carol S. Day & Pamela D. Swan(2002)Postprandial Thermogenesis Is Increased 100% on a High-Protein, Low-Fat Diet versus a High-Carbohydrate, Low-Fat Diet in Healthy, Young Women, Journal of the American College of Nutrition, 21:1, 55-61.
7. Neal, E.G., Chaffe, H., Schwartz, R.H., Lawson, M.S., Edwards, N., Fitzsimmons, G., Whitney, A. and Cross, J.H. (2009), A randomized trial of classical and medium-chain triglyceride ketogenic diets in the treatment of childhood epilepsy. Epilepsia, 50: 1109-1117.
8. Bolla AM, Caretto A, Laurenzi A, Scavini M, Piemonti L. Low-Carb and Ketogenic Diets in Type 1 and Type 2 Diabetes. Nutrients. 2019; 11(5):962.
9. Vanegas, A. P. P. A literature review on the effects of the ketogenic diet on the gut microbiota and weight-loss. Cantaurus May 2021; Vol. 29, 45-50.
10. Lim, J. M., Letchumanan, V., Tan, L. T. H., Hong, K. W., Wong, S. H., Ab Mutalib, N. S., … & Law, J. W. F. (2022). Ketogenic Diet: A Dietary Intervention via Gut Microbiome Modulation for the Treatment of Neurological and Nutritional Disorders (a Narrative Review). Nutrients, 14(17), 3566.
11. Jackson Aeja, Forsyth Christopher B., Shaikh Maliha, Voigt Robin M., Engen Phillip A., Ramirez Vivian, Keshavarzian Ali. Diet in Parkinson’s Disease: Critical Role for the Microbiome. Frontiers in Neurology. 2019; Vol. 1.