Microbial cells in our body outnumber human cells 10 to 1. They comprise about one and a half kilograms in our gut and they also cover our skin and mucous membranes. (1) The fact that so many of our cells are microbial has got many research laboratories looking at some of the ramifications of having the wrong bacterial balance in the gut. A very important one is the association between the wrong bacteria and weight gain or obesity.
So why does the wrong bacterial balance in the gut cause an increase in weight? There appear to be major individual differences in the makeup of the gut flora among obese and lean subjects, with the key being that the pathogenic bacteria which predominate in obese subjects are actually much more efficient in extracting and storing energy from food. (2) The hypothesis would seem to be confirmed by the observation that when people lose weight their gut bacteria change back to the more healthy strains observed in a lean person. (3) So there is a metabolic dialogue between the gut bacteria and the host.
Our gut microbiota is usually comprised of two main types of bacteria from the subkingdoms Firmicutes and Bacteroidetes. (2) The Firmicutes are a group of bacteria which are able to ferment non-digestible food components in the lower bowel (such as fibre and pectin) into short-chain fatty acids and monosaccharides using glycoside hydrolases and polysaccharide lysases.(4) When the bacteria from a group of over-weight animals are transplanted into the sterilized guts of lean animals there is a 60% increase in body fat in those animals over 2 weeks. (5) This is accompanied by increased insulin resistance, adipocyte hypertrophy and increased levels of circulating leptin and glucose. These bacteria are also able to boost anabolic processes linked to triglyceride production and lipoprotein lipase-driven fatty acid storage. In short, there is an increase in energy gain and fat deposition in an obese animal coming from the wrong bacterial balance in the gut.
This also applies to humans. Gut flora is a key consideration in the management of pregnancy and neonates. Though the fetus carries no bacteria, newborns are colonized at birth through the birth canal and breast milk. (1) Research suggests that intake of probiotics during pregnancy may reduce the frequency of gestational diabetes from 36% to 13%. (6) and that women who take Lactobacilli and Bifidobacteria during the first trimester of pregnancy lose weight more quickly after the birth and have lower central obesity after one year. (7) Practitioners dealing with childhood obesity might note the research indicating that overweight children at age 7 have lower levels of good bacteria such as bifidobacteria and higher levels of bad bacteria such as Staphylococcus aureus compared to normal weight kids.(8) The Firmicutes have been shown to predominate in obese people and there is a decrease in the Bacteroidetes. After weight loss there is a significant increase in Bacteroidetes (5)
So what does all this mean for the person wanting to lose weight? Firstly, it may mean that if a calorie restricted diet is not working it may be due to the wrong balance of bacteria in the gut. On the other hand, over-eating is one important factors which causes a decrease in friendly microorganisms such as bifidobacteria as well as increasing pro-inflammatory bacteria associated with low grade inflammation which is classically associated with obesity and its co-morbidities.(4) There is presently no magic bullet but when embarking on a weight-loss program it may be wise to start incorporating into the diet anti-inflammatory probiotics such as lactobacillus acidophilus and bifidobacterium lactis which have shown good results in body fat loss studies. (9,10) High satiety soluble fibres such as low energy density polysacchaide prebiotics have also been found to be helpful.
1 Ainsworth C I am Legion. New Scientist 44-46, 14 May 20011
2 Turnbaugh PJ, Ley RE, Mahowald MA, et al An obesity-associated gut microbiome with increased capacity for energy harvest. Nature 2006:444,1009-10
3 Ley RE, Turnbaugh PJ, Klein S, et al. Microbial ecology: human gut microbes associated with obesity. Nature 2006: 444, 1022-3
4 Delzenne NM, Cani PD. The role of intestinal microbiota in energy metabolism and metabolic disorders. Int Diabetes Monitor 2010:22(5) 189-195
5 DiBaise JK, Zhang H, Crowell MD et al. Gut microbiota and its possible relationship with obesity Mayo Clin Proc 2008: 83(4) 460-469
6 Luoto R, Laitien K, Nermes M, et al. Impact of maternal probiotic-supplemented dietary counselling on pregnancy outcome and prenatal and postnatal growth: a double-blind placebo controlled study British J Nutrition 2010: 103,1792 1799
8 Kalliomaki M, Collado MC, Salminen S et al. Early differences in fecal micrbiota composition in children may predict overweight Am J Clin Nutr 2008;87,534-8