There isn’t much research looking at whether low-carbohydrate diets increase the risk of constipation, though a few studies suggest they can lead some people to develop constipation.
One 24-week randomized controlled trial assigned 120 people to follow either a low-carbohydrate or low fat diet for the purposes of weight loss.[1] Ultimately, more people self-reported constipation on the low-carbohydrate diet (68%) than on the low-fat diet (35%).
Another randomized controlled trial had 135 people follow either a low-carbohydrate diet or a low-fat, higher-fiber diet, with both being fairly low calorie (around 1,000–1,400 calories per day).[2] After three months, 23% of participants assigned to the low-carbohydrate diet had reported constipation, compared to only 3% on the low-fat, higher-fiber diet.
Finally, a three-month randomized controlled trial assigned 34 people with type 2 diabetes or prediabetes to either a low-carbohydrate, ketogenic diet or a calorie restricted diet based on diet guidelines by the American Diabetes Association.[3] By the end of the study, participants on the low-carbohydrate diet reported an increase in constipation symptoms.
Why exactly a low-carbohydrate diet might lead to constipation is unclear, but given that in practice such diets often lead people to eat less fiber,[4] it’s reasonable to wonder if this is a factor. In line with this, one of the three previously referenced trials assessed participants’ fiber intake, reporting that fiber intake decreased in the low-carbohydrate diet (from 17.1 to 13.9 grams per day), whereas it very slightly increased in the low-fat group (from 17.4 to 18.6 grams per day).[2]
Of course, it’s important to note that all studies were in the context of people losing weight (and all studies reported greater weight loss with the low-carbohydrate diet), meaning the low-carbohydrate diet involved calorie restriction. Whether a non-calorically reduced low-carbohydrate diet has the same effect on constipation is therefore not as clear.
Constipation is also a frequently reported side effect of ketogenic diets for childhood epilepsy.[5]
References
- ^Yancy WS, Olsen MK, Guyton JR, Bakst RP, Westman ECA low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia: a randomized, controlled trial.Ann Intern Med.(2004-May-18)
- ^Baron JA, Schori A, Crow B, Carter R, Mann JIA randomized controlled trial of low carbohydrate and low fat/high fiber diets for weight loss.Am J Public Health.(1986-Nov)
- ^Laura R Saslow, Sarah Kim, Jennifer J Daubenmier, Judith T Moskowitz, Stephen D Phinney, Veronica Goldman, Elizabeth J Murphy, Rachel M Cox, Patricia Moran, Fredrick M HechtA randomized pilot trial of a moderate carbohydrate diet compared to a very low carbohydrate diet in overweight or obese individuals with type 2 diabetes mellitus or prediabetesPLoS One.(2014 Apr 9)
- ^Storz MA, Ronco ALNutrient intake in low-carbohydrate diets in comparison to the 2020-2025 Dietary Guidelines for Americans: a cross-sectional study.Br J Nutr.(2022-Jun-22)
- ^Martin-McGill KJ, Jackson CF, Bresnahan R, Levy RG, Cooper PNKetogenic diets for drug-resistant epilepsyCochrane Database Syst Rev.(2018 Nov 7)