Saturday, 11 June 2011

Obesity, gut bacteria and WALL-E

I quite openly admit that I quite enjoy watching the odd Disney film as part of family life (as part of family, yeah, for the family). If Disney ever decided to give out accolades for the most times watching the various films of the Toy Story trilogy, I'd like to believe that I would be in with a medal chance, having watched them, or part of them, several hundred times as part of some positive reinforcement procedures currently in place in my house. In recent times our household attentions have been focussed on Disney's WALL-E and his particular take on marvels of humankind. It was whilst watching this for about the 30th time or so, that I realised the quite important message in the movie about humans, technology and dependency; and what could happen when we become over-reliant, particularly on our physicality and the risk of becoming overweight or obese.

With this in mind and continuing my current theme looking slightly outside of autism research to some new studies looking at the various risk factors for being overweight and obesity I offer a little discussion on this study* published in the journal Gut Pathogens. I say that this post is outside of autism, but as you might see, the results may be just as relevant to those with an autism spectrum condition as they are to anyone else.

The study looked at faecal samples taken from infants at various stages in their first year at the same time assessing their body mass index (BMI) up to age 3. The intention was to see whether early infantile gut bacteria might be a marker for obesity on the back of some previous research in this area. The details: 138 children were initially admitted for study. They were all uncomplicated NVD births recruited from various maternity clinics in Belgium. BMI measures were taken by parental questionnaire based on clinical measures carried out at 12, 18, 24,30 & 36 months. Faecal samples were collected and cultured for various bacterial species and the various results correlated as a function of age (3, 26 & 52 weeks).

There are a few results which are noteworthy, some tied into the main study and some just plain interesting:

  • Of the total cases, nearly 45% of mother smoked before pregnancy and nearly 10% during pregnancy.
  • Antimicrobial use at 3 weeks was low (only 1.5% of infants) but by 1 year, just over 50% of the sample had received at least one course of antibiotics.
  • Most cultured bacterial species seemed to show an increase post 3 weeks although perhaps plateauing between 26 & 52 week testing periods. Bacteroides fragilis showed the greatest increase in median species count from week 3 to week 52. Interestingly only trace or very low levels of Lactobacillus was found between the testing occasions (whether this facultative anaerobe might have been affected by the anaerobic collection and storage condition of samples, I don't know).
  • Bacteroides fragilis was positively correlated with BMI in pre-school children, and where high levels were noted at the same time as low levels of Staphylococcus, there was a significant association with higher BMI during the first 3 years of life.

I highlighted the smoking aspect of things because maternal smoking, whether pre- or peri-natally, has been linked to later offspring obesity before. The current study did control for such factors when analysing their correlative data. The use of antimicrobials was again something controlled for during the study; more than that however I was just taken aback by the fact that 50% of children aged 1 year old had some history of use. I am not a Medic so don't have any experience of prescribing patterns of antimicrobials - maybe this figure is not so high to those who are involved in pediatric care? Nevertheless, there are some suggestions that such early antimicrobial use might be linked to an increased risk of various things (like allergic disease and gastrointestinal inflammatory disease) although the evidence base is far from conclusive.

The bacterial results are interesting. From the data, it would suggest that the species examined seem to show quite an early colonisation of the infant gut which importantly doesn't seem to deviate too much once there (bearing in mind only 3 testing sessions were undertaken). Other studies have indicated similar findings also. Elevated BMI values relating to 'ratios' of bacterial colonies is the main event from the paper. The results perhaps conflict with other papers looking specifically at Bacteroides such as this one which reported lower levels of the generic species was associated with obesity in adults. The pretty important differences between these papers were however ethnicity, age and the lack of ratio correlation specifically including Staphylococcus. I say this, but where examinations of Staph has also been included in the experimental design, there is still a degree of inconsistency between the current findings and other results where an opposite relationship has been noted (low Bacteroides and high Staph numbers) amongst other things (again with caveats on the participant group under observation, etc).

The evidence does seem to be mounting up to suggest that gut bacteria shows at least a correlation with quite a few conditions; dare I say, particularly those where prevalence seems to have increased markedly over the last 20-30 years or so. Obesity, like many of these modern day conditions, is probably not solely down to gut bacteria but rather influenced by a complicated patterns of events including food availability and the type and quality of food that we produce nowadays coupled with our increasing inactivity vis-a-vis WALL-E.

To end, a spot of WALL-E and EVA dancing.

*Vael C. et al. Intestinal microflora and body mass index during the first three years of life: an observational study. Gut Pathogens. May 2011.