Considerations for the design and conduct of human gut microbiota intervention studies relating to foods.

With the growing appreciation for the influence of the intestinal microbiota on human health, there is increasing motivation to design and refine interventions to promote favorable shifts in the microbiota and their interactions with the host. Technological advances have improved our understanding and ability to measure this indigenous population and the impact of such interventions. However, the rapid growth and evolution of the field, as well as the diversity of methods used, parameters measured and populations studied, make it difficult to interpret the significance of the findings and translate their outcomes to the wider population. This can prevent comparisons across studies and hinder the drawing of appropriate conclusions. This review outlines considerations to facilitate the design, implementation and interpretation of human gut microbiota intervention studies relating to foods based upon our current understanding of the intestinal microbiota, its functionality and interactions with the human host. This includes parameters associated with study design, eligibility criteria, statistical considerations, characterization of products and the measurement of compliance. Methodologies and markers to assess compositional and functional changes in the microbiota, following interventions are discussed in addition to approaches to assess changes in microbiota-host interactions and host responses. Last, EU legislative aspects in relation to foods and health claims are presented. While it is appreciated that the field of gastrointestinal microbiology is rapidly evolving, such guidance will assist in the design and interpretation of human gut microbiota interventional studies relating to foods.

A Fraxinus excelsior L. seeds/fruits extract benefits glucose homeostasis and adiposity related markers in elderly overweight/obese subjects: a longitudinal, randomized, crossover, double-blind, placebo-controlled nutritional intervention study.

PURPOSE: The aim of this study was to investigate the potential benefits of an extract obtained from seeds/fruits of an Oleaceae (Fraxinus excelsior L.) on glucose homeostasis and associated metabolic markers in non-diabetic overweight/obese subjects. MATERIALS AND METHODS: This study was performed in 22 participants (50-80 years-old; BMI 31.0 kg/m(2)). The design was a longitudinal, randomized, crossover, double-blind, placebo-controlled 7-week nutritional intervention. The participants received daily 3 capsules each containing either 333 mg of an extract from Fraxinus excelsior L. seeds (Glucevia(®)) or placebo capsules (control) in a random order for 3 weeks with 1 week of washout between treatments. Moreover, they followed a balanced covert energy-restricted diet (-15% energy). All variables were measured at the beginning and at the end of each period. RESULTS: Compared to baseline, the administration of 1 g of Glucevia(®) for 3 weeks resulted in significantly lower incremental glucose area under the curve (-28.2%; p<0.01), and significantly lower 2 h blood glucose values (-14%; p<0.01) following an oral glucose tolerance test. No significant changes were found in the control group (-7.9% AUC, -1.6% 2h blood glucose). Furthermore, significant differences were found between responses in the control and Glucevia(®) groups with respect to serum fructosamine and plasma glucagon levels (p<0.01 and p<0.05, respectively). Interestingly, administration of Glucevia(®) significantly increased the adiponectin:leptin ratio (p<0.05) and decreased fat mass (p<0.01) compared to control (p<0.05). CONCLUSION: The administration of an extract from Fraxinus excelsior L. seeds/fruits in combination with a moderate hypocaloric diet may be beneficial in metabolic disturbances linked to impaired glucose tolerance, obesity, insulin resistance and inflammatory status, specifically in older adults.