“The causes that drive obesity appear to be complex” (Angelakis, et al. 2012) may be the understatement of the nutrition field. Lifestyle factors (diet, exercise, etc), host biological factors (genes, hormonal and neurological responses) and colonizing microbes all have a roll to play in what some consider the biggest nutrition crisis of our day. (See Obesity is a bigger health crisis than hunger.)
A new chapter to this discussion opened when Raoult and colleagues (Million, et al. 2012) proposed that consumption of Lactobacillus was linked to increased obesity. As a person who has spent the last 20+ years delving into literature on probiotics, I was concerned that perhaps the myriad of potentially positive benefits associated with consumption of Lactobacillus could be countered by such an ominous downside. This would deal a serious blow to the probiotic field.
So what is known on this issue?
- Certain Lactobacillus species (e.g., L. reuteri) decrease intestinal infections and improve weight gain in farm animals
- Certain Lactobacillus also decrease intestinal infections in infants and children.
- Diet composition has an important effect on microbiota composition, making it hard to distinguish changes driven by diet from any that may be associated with the obese state.
- Microorganisms in the large intestine may contribute to energy available from food by fermenting otherwise indigestible components of the diet.
- Gut microorganisms and their metabolic products may influence gut hormones, inflammation, and gut motility.
- Gut microbes may reduce infections, thereby increasing healthy gut function and thereby improving harvest of energy from foodstuffs.
- Microbial metabolites or microbial cell-derived signals may impact host pathways that regulate energy intake and/or fat deposition.
Clearly, gut microbes, and potentially probiotics, which can become transient members of the gut microbial community, have the capacity to impact energy balance through different mechanisms. However, we must realize that weight gain per se is not bad. People need to gain weight throughout infancy and childhood. What is bad is accumulated fat mass as we age. The paper by Million, et al. (2012) does not provide evidence of this occurrence. See Lahtinen et al. (2012). In fact, evidence for the contrary exists. Kadooka et al (2013) published a multi-center, double-blind, randomized controlled trial that demonstrated that Lactobacillus gasseri SBT2055, as part of a fermented milk consumed over 12 weeks, reduced abdominal visceral fat, BMI, waist and hip circumferences, and body fat mass compared to control. Similar results were observed in an earlier study using a higher daily dose (2×1010 cfu/d) of the probiotic (Kadooka, et al. 2010). The hypothesis by Million would suggest that the Lactobacillus-consuming group should have increased these measures.
A recent article in Nature documents archaeological evidence that humans had figured out how to make cheese 7000 years ago. It just does not seem probable that this long association with fermentation microbes, many of which are Lactobacillus strains, is contributing to our obesity epidemic in the 21st century.
Angelakis E, Armougom F, Million M, Raoult D. The relationship between gut microbiota and weight gain in humans. Future Microbiol. 2012 Jan;7(1):91-109.
Delzenne NM, Cani PD. Interaction between obesity and the gut microbiota: relevance in nutrition. Annu Rev Nutr. 2011 Aug 21;31:15-31.
Kadooka Y, Sato M, Imaizumi K, Ogawa A, Ikuyama K, Akai Y, Okano M, Kagoshima M, Tsuchida T. Regulation of abdominal adiposity by probiotics (Lactobacillus gasseri SBT2055) in adults with obese tendencies in a randomized controlled trial. Eur J Clin Nutr. 2010 Jun;64(6):636-43.
Kadooka Y, Sato M, Ogawa A, Miyoshi M, Uenishi H, Ogawa H, Ikuyama K, Kagoshima M, Tsuchida T. Effect of Lactobacillus gasseri SBT2055 in fermented milk on abdominal adiposity in adults in a randomised controlled trial. Br J Nutr. 2013 Apr 25:1-8.
Lahtinen SJ, Davis E, Ouwehand AC. Lactobacillus species causing obesity in humans: where is the evidence? Benef Microbes. 2012 Sep;3(3):171-4.
Million M, Angelakis E, Paul M, Armougom F, Leibovici L, Raoult D. Comparative meta-analysis of the effect of Lactobacillus species on weight gain in humans and animals. Microb Pathog. 2012 Aug;53(2):100-8.