Question

Mary starts the keto diet. She is expereincing constipation and cranping. How does the keto diet affect her GI microbiome and overall GI tract health?

Answer 1

A ketogenic diet is a low carb high-fat diet that permits the use of very less amount of carbohydrates (5% to 10% of total caloric intake) which enhances the production of ketone and puts the body in a metabolic state of ketosis. After several days on this type of diet, glucose in the body becomes insufficient for the oxidation of fats and for energy production in CNS forcing the body to use fat as the primary fuel energy source. Since fat-free acids cannot cross the blood-brain barrier they cannot provide energy to the CNS. Ketone bodies produced in the liver come to the rescue then. A ketogenic diet helps to burn fat but the main side effect is constipation because of the presence of fewer fibers in the diet.

Effect of the keto diet (KD) on GI health and microbiome

KD has a contradictory role in hunger but the net effect is anorexigenic.

Orexigenic effects of KD

• increases brain GABA
• increase of AMP phosphorylation
• increase in circulating levels of adiponectin
• a decrease in reactive oxygen species

Anorexigenic effects of KD

• increase in circulating post-meal free fatty acids
• a decrease in agouti-related protein expression.

Role in fat loss

• decrease of lipo-synthesis
• increase in lipid oxidation and adiponectin

KD has a contradictory role in effect on the gut microbiome. KD exerts its effect through an increase in diversity in a single ecosystem and a decrease in richness i.e., the number of different species in a habitat.

KD influences gut health through metabolites produced by different microbes i.e., an increase/decrease in short-chain fatty acids, an increase in hydrogen sulfide, a decrease in lactate.

KD's effects on the brain are mediated by microbiota through the increase of short-chain fatty acids and a decrease of gamma-glutamyl amino acid.

There is an increase in A. muciniphila and Lactobacillus spp responsible for producing short-chain fatty acids leading to a reduction in body weight and glycemia. Desulfovibrio has the ability to impair the intestinal mucosal barrier by producing hydrogen sulfide.

Conclusion

Diets with high-fat content, good quality of polyunsaturated fats, and plant-derived proteins can maintain normal gut function. Alongside the abolition of artificial sweeteners is recommended as it has a negative impact on gut health and microbiota composition. Supplementation with prebiotics such as inulin, lactulose, etc. that increases Bifidobacteria should be taken to prevent undesired changes in gut microbiota.