Diets and microbiota - The ketogenic diet (keto)

Blog, Weight management, Inflammation, Digestive health

In a world where diets are multiplying, the ketogenic (or keto) diet is attracting increasing attention. But what are its effects on intestinal microbiota and digestive health?

Here's a series of blogs about three diets and their impact on the gut microbiota. This one is about the ketogenic (keto) diet.

The other two cover the topics listed in the following links:

It should be noted that the reasons for adhering to this type of diet, such as its effects on diabetes and weight loss, are not covered in these blogs. However, a medical conference on the subject is available. Contact us if you're interested.

What is the ketogenic diet?

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Definition Low carb, high fat diet (3)(7). The efficacy of the ketogenic diet in refractory epilepsy has been documented for several years.

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Objective Creating ketone bodies used as a source of energy from fatty acids (11).

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Food proportions Up to 60 % of calories come from lipids or fats, with a carbohydrate intake of between 20 and 50 g per day (3)(7)(11).

Here is a brief overview of the foods targeted in this diet

Foods to favour
  • Fats: butter, oils, cream
  • Olives, avocado
  • Red meat and cold cuts, poultry, fish and seafood, eggs
  • Nuts, seeds, nut butter
  • Low-carb vegetables and fruit (e.g. green vegetables, peppers, berries)
Foods to avoid
  • Starches and grains: rice, bread, pasta, quinoa, crackers
  • Milk, yogurt
  • Pulses
  • Added sugars: cookies, desserts, pastries
  • Root vegetables and carbohydrate-rich fruits (e.g. carrots, squash, bananas)

Possible risks of the ketogenic diet

Adherence to the ketogenic diet carries certain risks and side effects for gut and overall health, including (2)(3)(4)(5)(6)(7)(9)(11):

  • Digestive disorders: constipation, diarrhea (keto flu), bloating, nausea, vomiting, gastritis;
  • Fatigue, headaches, muscle cramps;
  • Hepatitis, pancreatitis;
  • Increased serum uric acid (gout), electrolyte disorders such as hyponatremia or hypomagnesemia;
  • Hypoglycemia, hypotension, change in breath, dehydration;
  • Potential long-term effects on kidneys, heart and bones;
  • Nutritional deficiencies: Vitamins A, B, C, D, E, minerals Ca, Fe, K, Mg and fiber.

Contraindications of the ketogenic diet

There are also certain contraindications to following the ketogenic diet. Here are some of them (3)(5)(7) :

Absolute contraindications
  • Carnitine palmitoyltransferase I or II deficiency
  • Carnitine translocase deficiency
  • Defects in fatty acid beta-oxidation
  • Long-chain 3-hydroxyacyl-CoA deficiency
  • Organic acidurias
  • Porphyria
Possible contraindications
  • Cancer
  • Diabetes
  • Eating Disorders (ED)
  • Familial hypercholesterolemia
  • Gastroesophageal reflux disease (GERD)
  • Gout, kidney stones
  • Children, pregnant women

Impact of the ketogenic diet on the intestinal microbiota

The scientific literature points to several negative effects of the ketogenic diet on the intestinal microbiota :

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Reduction in total bacterial abundance and diversity A rich and diverse microbiota is associated with good digestive health (4)(9)(10)(11).

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Decrease in beneficial bacteria : Bifidobacteria, Firmicutes, Lactobacillus, and Faecalibacterium prausnitzii, which support the intestinal and overall health (1)(4)(8)(9)(10)(11).

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Reduction of short-chain fatty acids (AGCC) fecal totals These compounds, produced by the fermentation of fibers, are beneficial to intestinal health (8)(9).

Various possible mechanisms

Why does the ketogenic diet have such a negative effect on the microbiota?

Carbohydrate reduction

Lower consumption of dietary fibers (found in starchy foods, fruits and vegetables, which should be reduced/avoided in the ketogenic diet) limits the fermentation by intestinal bacteria (8)(9). By fermenting fiber less, «good» bacteria are less present (e.g. Bifidobacteria, Firmicutes) and thus produce «less» beneficial molecules such as AGCC (1)(4)(8)(9)(10)(11).

Increase in potentially harmful bacteria

A proliferation of potentially harmful bacteria such as Bacteroidetes and Alistipes is often observed (1)(4)(9)(10).

Consequences for intestinal permeability

A reduction in SCFAs has the potential to deteriorate the intestinal mucus barrier, making the intestinal barrier more «permeable» (8)(10). Increased intestinal permeability is associated with digestive disorders and chronic inflammation.

Limits of current research

Lack of human studies

Research is mainly based on small-scale, often short-term studies (8).

Difficult long-term adhesion

The ketogenic diet is difficult to follow over the long term, particularly because of social events and family meals (4).

Heterogeneity of studies

The impact of diet may vary from one individual to another, depending on their initial bacterial profile (8). Many factors influence the microbiota (e.g. diet, environment, age, disease), and some studies have not considered all of them (8).

Towards new research

Further, longer-term studies in humans are needed to understand the impact of the ketogenic diet on different conditions such as irritable bowel syndrome (IBS), Inflammatory Bowel Disease (IBD) and mental health problems (e.g. depression).

In conclusion

  • The ketogenic diet seems to have more adverse effects on the gut microbiota, reducing bacterial diversity and richness, with risks for digestive health.
  • Before adopting this diet, it is essential to consult a healthcare professional to assess the risks and determine whether it's right for your specific needs, especially in the case of digestive disorders and intestinal discomforts such as gastro-oesophageal reflux disease (GERD).

References

(1) Borrego-Ruiz and Borrego (2024) Human gut microbiome, diet, and mental disorders. Int Microbiol Apr 1. https://pubmed.ncbi.nlm.nih.gov/38561477/
(2) Dyńka et al. (2023) Effect of the Ketogenic Diet on the Prophylaxis and Treatment of Diabetes Mellitus: A Review of the Meta-Analyses and Clinical Trials. Nutrients Jan 18;15(3):500. https://pubmed.ncbi.nlm.nih.gov/36771207/
(3) Hull et al (2019) Evidence-based Keto Your no-hype guide to the ketogenic diet. Examine.
(4) Mohammadifard et al. (2022) The Effect of Ketogenic Diet on Shared Risk Factors of Cardiovascular Disease and Cancer. Nutrients Aug 25;14(17):3499. https://pubmed.ncbi.nlm.nih.gov/36079756/
(5) Muscogiuri et al (2021) Obesity Management Task Force (OMTF) of the European Association for the Study of Obesity (EASO). European Guidelines for Obesity Management in Adults with a Very Low-Calorie Ketogenic Diet: A Systematic Review and Meta-Analysis. Obes Facts 14( 2 ):222-245. https://pubmed.ncbi.nlm.nih.gov/33882506/
(6) Nuwaylati et al. (2022) Low-Carbohydrate High-Fat Diet: A SWOC Analysis. Metabolites Nov 17;12(11):1126. https://pubmed.ncbi.nlm.nih.gov/36422267/
(7) Patel (2019) Ketogenic diet. Examine.
(8) Rew et al. (2022) The ketogenic diet: its impact on human gut microbiota and potential consequent health outcomes: a systematic literature review. Gastroenterol Hepatol Bed Bench 15( 4 ):326-342. https://pubmed.ncbi.nlm.nih.gov/36762214/
(9) Rinninella et al. (2019) Food Components and Dietary Habits: Keys for a Healthy Gut Microbiota Composition. Nutrients Oct 7;11(10):2393. https://pubmed.ncbi.nlm.nih.gov/31591348/
(10) Rinninella et al. (2023) The role of diet in shaping human gut microbiota. Best Pract Res Clin Gastroenterol Feb-Mar;62-63:101828. https://pubmed.ncbi.nlm.nih.gov/37094913/
(11) Santangelo et al (2023) The Influence of Ketogenic Diet on Gut Microbiota: Potential Benefits, Risks and Indications. Nutrients Aug 22;15(17):3680. https://pubmed.ncbi.nlm.nih.gov/37686712/