Malnutrition continues to threaten the lives of millions across the world, with children being hardest hit. Although inadequate access to food and infectious disease are the primary causes of childhood malnutrition, the gut microbiota may also contribute. This review considers the evidence on the role of diet in modifying the gut microbiota, and how the microbiota impacts childhood malnutrition. It is widely understood that the gut microbiota of children is influenced by diet, which, in turn, can impact child nutritional status. Additionally, diarrhoea, a major contributor to malnutrition, is induced by pathogenic elements of the gut microbiota. Diarrhoea leads to malabsorption of essential nutrients and reduced energy availability resulting in weight loss, which can lead to malnutrition. Alterations in gut microbiota of severe acute malnourished (SAM) children include increased Proteobacteria and decreased Bacteroides levels. Additionally, the gut microbiota of SAM children exhibits lower relative diversity compared with healthy children. Thus, the data indicate a link between gut microbiota and malnutrition in children, suggesting that treatment of childhood malnutrition should include measures that support a healthy gut microbiota. This could be of particular relevance in sub-Saharan Africa and Asia where prevalence of malnutrition remains a major threat to the lives of millions.

Dietary periodization is employed to improve endurance exercise performance but may impact on gut microbial communities. Bacteriophage are implicated in bacterial cell homeostasis and have been identified as biomarkers of disequilibrium in the gut ecosystem possibly brought about through dietary periodization.

The objective of this systematic literature review was to evaluate the efficacy of probiotic, prebiotic, and synbiotic interventions compared to control on improving growth outcomes of children living in low-and middle-income countries (LMICs). Probiotics had a beneficial effect on at least one of the growth outcomes in five out of the eleven included studies. Of these, three studies were conducted in undernourished children, one in healthy children, and one in children without a described health status. No effect of prebiotics on the growth outcomes was seen in the four included studies. Synbiotics had a beneficial effect on growth outcomes in three out of four studies. While a limited number of studies with high heterogeneity indicate that probiotics and synbiotics may have the potential to improve the growth of both undernourished and healthy children living in LMIC, more research is needed to confirm the observed effects. The study was registered at the international prospective register of systematic reviews (PROSPERO, reg. no. CRD42020212998).

Manipulating dietary macronutrient intake may modulate adaptive responses to exercise, and improve endurance performance. However, there is controversy as to the impact of short-term dietary modification on athletic performance. In a parallel-groups, repeated measures study, 16 trained endurance runners (maximal oxygen uptake (V˙O2max): 64.2 ± 5.6 mL·kg−1·min−1) were randomly assigned to, and provided with, either a high-protein, reduced-carbohydrate (PRO) or a high-carbohydrate (CHO) isocaloric-matched diet. Participants maintained their training load over 21-consecutive days with dietary intake consisting of 7-days habitual intake (T1), 7-days intervention diet (T2) and 7-days return to habitual intake (T3). Following each 7-day dietary period (T1–T3), a micro-muscle biopsy was taken for assessment of gene expression, before participants underwent laboratory assessment of a 10 km treadmill run at 75% V˙O2max, n treadmill run at 70% vV˙O2max time to exhaustion (TTE) trial. The PRO diet resulted in a modest change (1.37-fold increase, p = 0.016) in AMPK expression, coupled with a significant increase in fat oxidation (0.29 ± 0.05 to 0.59 ± 0.05 g·min−1, p < 0.0001). However, a significant reduction of 23.3% (p = 0.0003) in TTE post intervention was observed; this reverted back to pre levels following a return to the habitual diet. In the CHO group, whilst no change in sub-maximal fuel utilisation occurred at T2, a significant 6.5% increase in TTE performance (p = 0.05), and a modest, but significant, increase in AMPK (p = 0.042) and PPAR (p = 0.029) mRNA expression compared to T1 were observed; with AMPK (p = 0.011) and PPAR (p = 0.044) remaining significantly elevated at T3. In conclusion, a 7-day isocaloric high protein diet significantly compromised high intensity exercise performance in trained runners with no real benefit on gene markers of training adaptation. A significant increase in fat oxidation during submaximal exercise was observed post PRO intervention, but this returned to pre levels once the habitual diet was re-introduced, suggesting that the response was driven via fuel availability rather than cellular adaptation. A short-term high protein, low carbohydrate diet in combination with endurance training is not preferential for endurance running performance.

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Combining the fibres wheat dextrin (WD), partially hydrolysed guar gum (PHGG) and inulin with probiotics Lactobacillus acidophilus NCFM (NCFM) or Bifidobacterium lactis HN019 (HN019) may enhance bacterial metabolites leading to a healthier gut community. The aim of this study was to determine whether WD, PHGG and inulin or NCFM and HN019 alone generate a more favourable gut bacterial community than when combined. A secondary aim was to assess organic acid production following prebiotics, probiotics and synbiotic fermentation. An in vitro gut model batch culture fermentation was run for 72h. Samples were collected for bacterial enumeration (fluorescent in situ hybridisation combined with flow cytometry) and organic acid production (gas chromatography). Inulin and HN019 combination significantly increased bifidobacteria compared to inulin alone. Additionally, a significant increase in lactic acid bacteria, Bacteroides and Clostridium coccoides-Eubacterium rectale was found in the inulin containing probiotic vessels. The WD and PHGG vessels combined with the probiotic did not show any alteration in bacterial metabolism compared to the dietary fibres alone. In conclusion, synbiotic inulin combined with either HN019 or NCFM may help to enhance bacterial metabolites and cross-feeding to lead to a prolonged elevation in Bifidobacterium spp., and lactic acid bacteria.