The composition of the gut microbiota has been associated with obesity in animal models and considered to be a potential environmental factor involved in this disorder(Reference Ley, Backhed and Turnbaugh¹). In the present preliminary study the composition of the faecal microbiota of obese and overweight adolescents (aged 14.8 (sd 1.3) years) was investigated initially and after following a nutritional intervention strategy based on an energy-restricted diet (30–40%) and a physical activity programme (energy expenditure 3762–11 286 kJ/week) for 3 months. Eight obese and overweight individuals were identified according to the International Obesity Task Force criteria(Reference Cole, Belizzy and Flegal²) in the frame of the EVASYON project. The microbiological analyses were carried out by fluorescent in situ hybridization, using oligonucleotide probes targeting the main microbial groups colonizing the human distal gut (Archaea, Bacteroides, Bifidobacterium, Clostridium coccoides–Eubacterium rectale, Clostridium leptum, Enterobacteriaceae, Enterococcus, Fusobacterium prausnitzii, Lactobacillus, Roseburia–Eubacterium, Ruminococcus and sulphate-reducing bacteria). Enterobacteriaceae and sulphate-reducing bacterial counts were significantly reduced (P<0.05) in faecal samples of individuals (n 5) showing remarkable reductions in their weight (4–7 kg) but not in those (n 3) showing minor weight losses (<2 kg) after the intervention. In contrast, this last group of children showed significantly lower (P<0.05) counts of Roseburia–Eubacterium populations. These gut microbes could play a role in obesity by affecting either the energy harvest from the diet(Reference Turnbaugh, Ley and Mahowald³) or the signalling pathways that link inflammation with obesity(Reference Bleau, Lamontagne and Savard⁴). Overall, the present preliminary study shows that modifications in the gut microecology are associated with corporal weight in adolescents under a similar energy-restricted diet. Investigations are in progress to confirm this trend and assess whether the intentional manipulation of the gut microbiota could be envisaged as a strategy to combat obesity and immune disorders resulting from obesity.

Table 1. Microbial composition of faeces from overweight and obese adolescents

Mean values were significantly different from initial values (Student's t test): *P<0.05.