In the first episode, we have briefly discussed the short history and current practices of ketogenic diet (KD) and why this diet has become so hyped and followed by many people. After discussing the physiological impact of KD in the following episode, we will now dive into the effect of ketogenic diet on the gut microbiota.
Human gut microbiota
According to Ursell et al. [1], human microbiota consists of 10-100 trillion microbial cells, primarily in the gastrointestinal (GI) tract, which comprises more than 70% of the microorganism colonization. The number of these microorganisms (bacteria, viruses, fungi) is collectively called microbiota, and the genes that harbor these cells comprise the human microbiome.
Studies have shown that intestinal floral greatly influences an individual's health and disease [2]. A growing number of studies have demonstrated the influence of gut microbiota on obesity, digestive disorders, inflammatory, endocrine, and auto-immune disorders [3]. The same study has shown how exercise and a diet rich in fiber, fruits, vegetables, whole grains, and legumes boosted the number of beneficial bacterial species, as well as increased overall diversity, which has a beneficial effect on the individual's health [3].
The effects of a KD on intestinal microbiota
Both positive and negative results of KD to the gut microbial health have been reported by several studies. Swidsinski A. et al. [4] analyzed the gut microbiota of 10 patients with multiple sclerosis (MS) on a KD for six months. Results showed a dramatic decrease in bacterial diversity and concentrations, but after 12 weeks, bacterial concentration began to recover back to baseline. After 23-24 weeks, a significant increase in the bacterial concentration above baseline was observed. Another study by Xie G. et al. [5] compared KD on 14 pediatric patients with refractory epilepsy to 30 healthy aged-matched infants. Patients with epilepsy demonstrated an imbalance of gut microbiota prior to starting the KD, especially having higher amounts of pathogenic Proteobacteria (Escherichia, Salmonella, and Vibrio), which significantly decreased after KD treatment. An increase of Bacteroidetes, mainly found in healthy infants, was also reported after treatment. This experiment showed that not only were symptoms of epilepsy mitigated, but also gut microbiota imbalances were corrected with KD.
Research, however, has also revealed some potential negative effects on the gut microbiota with subjects on a KD. A 2009 study by Brinkworth et al. [6] compared 91 overweight and obese subjects who were randomly assigned to either a hypo-caloric (30% deficit) iso-energetic low carbohydrate or high carbohydrate diet for 8 weeks. The goal was not only to assess changes in body composition between the diets, but also to assess the effects on bowel health. The low-carbohydrate group was found to have a significant reduction in faecal output, defecation frequency, concentration of butyrate, the total number of short chain fatty acids, as well as Bifidobacteria (a beneficial bacteria) for colon health. Short chain fatty acids, like butyrate, are generated by microbial fermentation and primarily used as energy source of colonocytes (epithelial cells of the colon). They have been associated with colonic health and protective against colorectal cancer.
Another concern is the restricted amount of dietary fibers, resistant starches, and non-digestible oligosaccharides in the high-fat low-carb KD. These components, which are present in plant-based foods severely restricted in KD, could promote gut health, besides vitamins, mineral, and potentially beneficial phytochemicals. Although vegetarian modification of KD may be available, shifting plant-based to animal-based diet, has been shown to alter the composition of gut microbiota [7].
Conclusion
There has been a growing interest in examining the effects of different diets on the gut microbiota. Diet has been shown to play a key role in influencing the overall bacterial composition and diversity. The effects of KD on gut microbiota have demonstrated mixed results, with some showing beneficial results with balancing bacterial composition, while others were reporting a decline in diversity and an increase in bacteria associated with inflammation. Future studies should focus on evaluating the long-term effects of a KD on the microbiota. Chronic exercise training may mitigate the decrease in diversity, which could offset any possible negative health consequences related to low gut diversity.
S.A.D Team
Reference
Ursell LK, Metcalf JL, Parfrey LW, Knight R. Defining the human microbiome. Nutrition reviews. 2012;70(suppl_1):S38-S44.
Clemente JC, Ursell LK, Parfrey LW, Knight R. The impact of the gut microbiota on human health: an integrative view. Cell. 2012;148(6):1258-70.
Villano I, Messina A, Valenzano A, Esposito T, Moscatelli F, Viggiano A, Cibelli G, Chieffi S, Monda M, Messina G. Exercise modifies the gut microbiota with positive health effects. 2017.
Swidsinski A, Dörffel Y, Loening-Baucke V, Gille C, Göktas Ö, Reißhauer A, Neuhaus J, Weylandt K-H, Guschin A, Bock M. Reduced mass and diversity of the colonic microbiome in patients with multiple sclerosis and their improvement with ketogenic diet. Frontiers in microbiology. 2017;8:1141.
Xie G, Zhou Q, Qiu C-Z, Dai W-K, Wang H-P, Li Y-H, Liao J-X, Lu X-G, Lin S-F, Ye J-H. Ketogenic diet poses a significant effect on imbalanced gut microbiota in infants with refractory epilepsy. World journal of gastroenterology. 2017;23(33):6164.
Brinkworth GD, Noakes M, Clifton PM, Bird AR. Comparative effects of very low-carbohydrate, high-fat and high-carbohydrate, low-fat weight-loss diets on bowel habit and faecal short-chain fatty acids and bacterial populations. British journal of nutrition. 2009;101(10):1493-502.
David LA, Maurice CF, Carmody RN, Gootenberg DB, Button JE, Wolfe BE, Ling AV, Devlin AS, Varma Y, Fischbach MA. Diet rapidly and reproducibly alters the human gut microbiome. Nature. 2014;505(7484):559-63.