Volume 189 - Issue 3
Probiotics: sorting the evidence from the myths
Author: Sanjaya N Senanayake
Med J Aust 2008; 189 (3): 182-183. || doi: 10.5694/j.1326-5377.2008.tb01970.x
Published online: 4 August 2008
Published online: 4 August 2008
To the Editor: Pham and colleagues commented on the effects of probiotics; however, not much is known about the impact of probiotics on weight gain and obesity. It is known that a predominance of certain bacteria, such as Lactobacillus, in the bowel can promote weight gain. Many of these bacteria are found in probiotic products.
The human intestinal microbiota is predominantly colonised by the Firmicutes and Bacteroidetes phyla of bacteria. Lactobacillus and Bifidobacterium, found in a number of probiotic products, belong to the Firmicutes phylum. A study has shown that obese people carry a higher proportion of bacteria from the Firmicutes phylum and that there is a statistically significant decrease in the proportion of Firmicutes bacteria as they lose weight.3 A similar pattern of Firmicutes predominance has been found in obese mice. Furthermore, the microbiota of the obese mice were more likely than those of lean mice to break down otherwise indigestible polysaccharides from the diet.4 In other words, a higher proportion of Firmicutes bacteria was associated with increased and more efficient caloric uptake from food.
These data did not necessarily imply causation, so the investigators performed another experiment. They transferred intestinal microbiota from obese and lean donor mice to germ-free mice, and found that the mice who received microbiota from the obese donors had a significant increase in body fat after 2 weeks compared with the recipients from the lean donors.4 It is therefore likely that the bacteria often found in probiotics can cause weight gain.
Obesity in children and adults is a major health problem in developed nations. Given the increasing use of probiotic products in such countries, large studies should be performed to characterise the association between probiotics and obesity. Such studies may not find any association or may find that there is only a dose-related risk. If there is an association, probiotics may still prove useful in certain circumstances (eg, for weight gain in children failing to thrive).
References
- Pham M, Lemberg DA, Day AS. Probiotics: sorting the evidence from the myths. Med J Aust 2008; 188: 304-308.
- Bajzer M, Seeley RJ. Physiology: obesity and gut flora. Nature 2006; 444: 1009-1010. 0_pgfId-1767713
- Ley RE, Turnbaugh PJ, Klein S, Gordon JI. Microbial ecology: human gut microbes associated with obesity. Nature 2006; 444: 1022-1023. 0_CBBCIIBH
- Turnbaugh PJ, Ley RE, Mahowald MA, et al. An obesity-associated gut microbiome with increased capacity for energy harvest. Nature 2006; 444: 1027-1031. 0_CBBFJCDG