Weight Loss and the Ketogenic Diet: What Does The Science Say?

Weight loss
Healthy eating
Three avocados stuffed with feta, tomatoes and mint

According to the 2020 Food and Health Survey published by the International Food Information Council (IFIC), a survey of more than 1,011 Americans, 43% of Americans follow a specific diet (1). The ketogenic diet is the 3rd most popular, with 8% of those surveyed following this diet (1), compared to 6% following this diet in 2019 and 3% in 2018 (2). This increase contrasts drastically with the 2020 report of the US news and World report magazine, ranking this diet 37th out of 39 according to an expert committee (3), making this diet one of the most fashionable and controversial. Is it a miraculous diet that is still poorly understood or a dangerous option? In order to better guide you, here is what the literature says about the impact of the ketogenic diet on weight loss.

1. Weight loss with the ketogenic diet?
It's proven... but only in the short term.

Compared to a low-fat diet, greater weight loss was observed from 6 to 24 months in participants following the ketogenic diet in 2 meta-analyses (4,5). However, there are some nuances that need to be mentioned regarding those results. According to one of the studies, this effect does not appear to be clinically significant after 24 months (4). The other study explained these results by a lower energy intake in participants on the ketogenic diet (5). Several other meta-analyses have been performed to compare the difference in weight loss between a low-carbohydrate and low-fat diet, but the results are inconsistent (6). 

These different results illustrate that the ketogenic diet has potentially interesting effects for weight loss, but the long-term effects still need to be demonstrated.  

2. The metabolic impact of the ketogenic diet

The effects of the ketogenic diet on low-density lipoproteins (LDL) are inconsistent, as researchers have noted both an increase and no impact (7). The same finding was made for high-density lipoproteins (HDL-C) and triglycerides (TG), i.e., an increase in these values or no significant difference was observed (7). These inconsistencies are explained by heterogeneity in macronutrient distribution, variable adherence of participants, as well as the variable amount of saturated fat in the diet (7). Those who value the ketogenic diet will mention that it has been observed that a higher intake of saturated fat would lead to an increase in LDL-C particle size and a decrease in apolipoprotein B (8), which would possibly protect against cardiovascular disease (9). However, further studies are needed to clarify the impact of saturated fat on cardiovascular disease. 

A similar finding has been made for insulin resistance; although glycated hemoglobin (HbA1C) is decreased in the short term (less than 6 months) compared to a low-fat diet, this difference diminishes at more than 1 year (7). A decrease in the use of oral hypoglycemic agents is also observed, but this finding is present for low carbohydrate diets in general and not the ketogenic diet (7).

Thus, although positive effects are observed in the short term, long-term effects remain to be demonstrated. The wide heterogeneity of studies regarding the type of diet prescribed (e.g., amount of carbohydrate or percentage of saturated fat), study protocols, variable health status of participants, generally short duration, small number of participants, high rate of non-adherence, and variability in the type of control groups greatly limit the interpretation of results. 

3. Is the ketogenic diet safe? 

Perhaps the greatest concern with the ketogenic diet is the potentially deleterious long-term impacts.

Some of the deleterious effects that have been documented in the short term are constipation, nausea, abdominal pain and flu-like side effects (commonly referred to as "keto flu") such as headaches, fatigue, nausea, dizziness and gastrointestinal discomfort (10). Typically, these symptoms are experienced during the first few weeks of the diet (10). Other commonly reported symptoms include dehydration, muscle cramps, halitosis, itching, diarrhea or constipation, urolithiasis or cholelithiasis (11,12). Long-term effects are yet to be demonstrated. 

A Dietitian: a food expert to help your clients choose the best option! 

In the New Canadian Clinical Practice Guidelines for Adult Obesity published in 2020 (13), it was concluded that

"no single nutritional intervention has been shown to be better than another and the literature continues to support that long-term adherence remains very important regardless of the intervention" (14).

In addition, systematic reviews and meta-analyses show that individualized nutrition interventions with a registered dietitian increase the amount of weight lost compared to standard recommendations or written materials (15). 

TeamNutrition dietitian will be able to choose with your patients the best approach according to their preferences, past experiences and social context in order to ensure a change of healthy and sustainable habits while cultivating a positive relationship with food. Do not hesitate to contact us to learn more about our services.


(1) International Food Information Council. 2020 Food & Health Survey. Juin 2020 (En ligne). https://foodinsight.org/2020-food-and-health-survey/
(2) International Food Information Council. Interest in Sustainability, Plant-Based Diets Among Trends in IFIC Foundation’s 2019 Food & Health Survey. (En ligne). https://foodinsight.org/wp-content/uploads/2019/05/2019-Food-and-Health…
(3) Us News and World Report. Best Diet Overall - Best Diets Us news and Wold report rakings. (En ligne). https://health.usnews.com/best-diet/best-diets-overall
(4) Bueno NB, de Melo IS, de Oliveira SL et da Rocha Ataide T. Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. Br J Nutr.2013;110(7):1178-1187.
(5) Mansoor N, Vinknes KJ, VeierØd MB etRetterstØl K. Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials. Br J Nutr.2016;115(3):466-479.
(6) Ting R, Dugré N, Allan MG et Lindblad AJ. Ketogenic diet for weight loss. Can Fam Physician.2018;64(12):906.
(7) Kirkpatrick CF, Bolick JP, Kris-Etherton PM 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.
(8) Krauss RM, Blanche PJ, Rawlings RS et al. Separate effects of reduced carbohydrate intake and weight loss on atherogenic dyslipidemia. Am J Clin Nutr. 2006;83(5):1025-1031.
(9) Otvos JD, Mora S, Shalaurova I et al. Clinical implications of discordance between low-density lipoprotein cholesterol and particle number, Clin Lipidol. 2011;5(2):105-113.
(10) Bostock ECS, Kirkby KC, Taylor BV et Hawrelak JA. Consumer Reports of “Keto Flu” Associated With the Ketogenic Diet. Front Nutr. 2020 Mar 13;7:20.
(11) Yancy WS, Olsen MK, Guyton JR 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(10):769-777.
(12) Muscogiuri G, Barrea L, Laudisio D et al. The management of very low-calorie ketogenic diet in obesity outpatient clinic: a practical guide. J Transl Med. 2019;17(1):356.
(13) Wharton S, Lau DCW, Vallis M et al. L’obésité chez l’adulte : ligne directrice de pratique clinique.CMAJ. 2020;192(49):E1757-E1775.
(14) Johnston BC, Kanters S, Bandayrel K, et al. Comparison of Weight Loss Among Named Diet Programs in Overweight and Obese Adults A Meta-analysis. JAMA. 2014;312(9):923-933. doi:10.1001/jama.2014.10397
(15) Williams L, Barnes K, Ball L et al. How Effective Are Dietitians in Weight Management? A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Healthcare. 2019;7(1):20.
Registered Dietitian Nutritionist