We investigated extreme changes in diet patterns on the gut microbiota of elite race walkers undertaking intensified training and its possible links with athlete performance. Numerous studies with sedentary subjects have shown that diet and/or exercise can exert strong selective pressures on the gut microbiota. Similar studies with elite athletes are relatively scant, despite the recognition that diet is an important contributor to sports performance. In this study, stool samples were collected from the cohort at the beginning (baseline; BL) and end (post-treatment; PT) of a three-week intensified training program during which athletes were assigned to a High Carbohydrate (HCHO), Periodised Carbohydrate (PCHO) or ketogenic Low Carbohydrate High Fat (LCHF) diet (post treatment). Microbial community profiles were determined by 16S rRNA gene amplicon sequencing. The microbiota profiles at BL could be separated into distinct “enterotypes,” with either a Prevotella or Bacteroides dominated enterotype. While enterotypes were relatively stable and remained evident post treatment, the LCHF diet resulted in a greater relative abundance of Bacteroides and Dorea and a reduction of Faecalibacterium. Significant negative correlations were observed between Bacteroides and fat oxidation and between Dorea and economy test following LCHF intervention.

Although the oral microbiota is known to play a crucial role in human health, there are few studies of diet x oral microbiota interactions, and none in elite athletes who may manipulate their intakes of macronutrients to achieve different metabolic adaptations in pursuit of optimal endurance performance. The aim of this study was to investigate the shifts in the oral microbiome of elite male endurance race walkers from Europe, Asia, the Americas and Australia, in response to one of three dietary patterns often used by athletes during a period of intensified training: a High Carbohydrate (HCHO; n = 9; with 60% energy intake from carbohydrates; ~8.5 g kg⁻¹ day⁻¹ carbohydrate, ~2.1 g kg⁻¹ day⁻¹ protein, 1.2 g kg⁻¹ day⁻¹ fat) diet, a Periodised Carbohydrate (PCHO; n = 10; same macronutrient composition as HCHO, but the intake of carbohydrates is different across the day and throughout the week to support training sessions with high or low carbohydrate availability) diet or a ketogenic Low Carbohydrate High Fat (LCHF; n = 10; 0.5 g kg⁻¹ day⁻¹ carbohydrate; 78% energy as fat; 2.1 g kg⁻¹ day⁻¹ protein) diet. Saliva samples were collected both before (Baseline; BL) and after the three-week period (Post treatment; PT) and the oral microbiota profiles for each athlete were produced by 16S rRNA gene amplicon sequencing. Principal coordinates analysis of the oral microbiota profiles based on the weighted UniFrac distance measure did not reveal any specific clustering with respect to diet or athlete ethnic origin, either at baseline (BL) or following the diet-training period. However, discriminant analyses of the oral microbiota profiles by Linear Discriminant Analysis (LDA) Effect Size (LEfSe) and sparse Partial Least Squares Discriminant Analysis (sPLS-DA) did reveal changes in the relative abundance of specific bacterial taxa, and, particularly, when comparing the microbiota profiles following consumption of the carbohydrate-based diets with the LCHF diet. These analyses showed that following consumption of the LCHF diet the relative abundances of Haemophilus, Neisseria and Prevotella spp. were decreased, and the relative abundance of Streptococcus spp. was increased. Such findings suggest that diet, and, in particular, the LCHF diet can induce changes in the oral microbiota of elite endurance walkers.

The effect of dietary FODMAP (fermentable oligo-, di- and mono-saccharides and polyols) in healthy adults is poorly documented. This study compared the specific effects of low and moderate FODMAP intake (relative to typical intake) on the faecal microbiome, participant-reported outcomes and gastrointestinal physiology. In a single-blind cross-over study, twenty-five healthy participants were randomised to one of two provided diets, ‘low’ (LFD) <4 g/d or ‘moderate’ (MFD) 14–18 g/d, for 3 weeks each, with ≥ 2-week washout between. Endpoints were assessed in the last week of each diet. The faecal bacterial/archaeal and fungal communities were characterised by eighteen participants from whom high-quality DNA was extracted by 16S rRNA and internal transcribed spacer 2 (ITS2) profiling and metagenomic sequencing. There were no differences in gastrointestinal or behavioural symptoms (fatigue, depression, anxiety) or faecal characteristics and biochemistry (including SCFA). Mean colonic transit time (telemetry) was 23 (95 % CI: 15, 30) h with the MFD compared with 34 (24, 44) h with LFD ( n 12; P = 0·009). Fungal diversity (richness) increased in response to MFD, but the bacterial richness was reduced, coincident with the expansion of the relative abundances of Bifidobacterium , Anaerostipes and Eubacterium . Metagenomic analysis showed expansion of polyol-utilising Bifidobacteria and Anaerostipes with MFD. In conclusion, short-term alterations of FODMAP intake are not associated with symptomatic, stool or behavioural manifestations in healthy adults, but remarkable shifts within the bacterial and mycobiome populations were observed. These findings emphasise the need to quantitatively assess all microbial domains and their interrelationships to improve understanding of the consequences of diet on gut function.

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