People tend to relate metabolism just with energy/weight, but it goes far beyond that.
To give an example, each cell within our body requires energy to function and considering energy is dependent on metabolism, it becomes the basis of how our entire body functions. There are many facets to disease but the common denominator of where most conditions start going ‘wrong’ is at a cellular level, which we then see presenting as signs and symptoms of disease.
The influence of the gut microbiome in metabolic pathways affecting weight management. The human intestinal microbiota is estimated to be composed of more than ten trillion microorganisms whose collective genome, the microbiome, contains at least 100-fold more genes than the complete human genome. The microbiome is ever changing and adapting, so we as the host environment need to be adept of these changes. Flora has many beneficial functions within the body such as improving digestive/absorptive capacity, producing important vitamins, fermenting SCFA’s, inhibiting growth of harmful bacteria, protecting the epithelial barrier and regulating the immune and nervous system. (Let alone taking into consideration what happens when the above functions become compromised, causing havoc on the system through toxic burden, hindered detoxification capacity, dysbiosis and malabsorption, to name a few). By understanding the mechanisms at play within our body, we are able to adjust our approach to greatly impact the effectiveness of our metabolism.
The idea is to achieve ‘homeostasis’ so that there are the right amounts and types of beneficial flora to defend the body from overgrowth of the not-so-beneficial flora. The more opportunistic (potentially unwanted) organisms take root and proliferate when there are ‘gaps’ in the flora. A number of factors need to be in check for there to be homeostasis such as pH, diet, digesting efficiently (dependent upon stomach acid, bile flow, enzyme production, elastase and pancreatic sufficiency), fermentable carbohydrates (fermented foods), soluble fibres, and beneficial & normal transit time without chronic low-grade inflammation.
Studies have now confirmed that flora has the ability to influence/change our metabolism:
“Antidiabetic drug alters lifespan of worms by altering the metabolism of their gut bacteria” lengthening it by a third of its normal lifespan.
(Dr Filipe Cabreiro – Institute of Healthy Ageing – UCL).
“Obesity is associated with phylum- level changes in the microbiota, reduced bacterial diversity and altered representation of bacterial genes and metabolic pathways. These results demonstrate that a diversity of organismal assemblages can nonetheless yield a core microbiome at a functional level, and that deviations from this core are associated with different physiological states (obese compared with lean)“ (Ley et al 2006)
It starts from the very beginning… 
Obesity results from alterations in energy balance —that is, how the body regulates energy intake, expenditure, and storage.
A group of researchers observed significant differences in gut microbiota composition according to the body weight during pregnancy. Interestingly, they found significantly higher numbers of Bacteroides group and S. aureus in the overweight state compared with normal-weight women, and they established a positive correlation between the number of Bacteroides on the one hand, and the weight and BMI (before and throughout pregnancy), on the other hand.
Bifidobacterium group was present in higher numbers in normal weight than in overweight women and also in women with lower weight gain over pregnancy. In addition, these researchers demonstrated that overweight mothers give birth to neonates that have a decreased number of Bifidobacteria. The infants’ faecal microbial composition was related to the weight and weight gain of their mothers during pregnancy. This finding may be related to the effect of colonisation at birth and/or inheritable obesogenic microbiota.
In breast-fed infants, the intestinal flora is dominated by Bifidobacteria, while formula fed infants have a more diverse flora.
We are what we eat… 
Accumulating evidence has suggested that host-gut microbial metabolic interactions can play an important role in predisposing individuals to obesity, which is mediated at least in part via an increase in the capacity of energy harvest from a given diet and induction of low-grade chronic systemic inflammation.
Studies have demonstrated that increased uptake of gut microbiota derived endotoxin/lipopolysaccharide (LPS) in mice fed a high fat diet (HFD) could lead to metabolic endotoxemia, which in turn may trigger obesity and insulin resistance.
However, quite interestingly, the LPS-mediated pathological conditions described above were ameliorated when the gut microbial homeostasis was modulated by prebiotic and probiotic treatments.
Accordingly, modulation of the gut microbiota distribution by probiotics/prebiotics is deemed a more effective and feasible strategy for control of obesity and its associated metabolic syndrome.
“Researchers at Massachusetts General Hospital have found that the gut microbes of mice undergo drastic changes following gastric bypass surgery. Transfer of these microbes into sterile mice resulted in rapid weight loss”… “We need to learn if we can produce these effects – either the microbial changes or the associated metabolic changes – without surgery”
(Peter Turnbaugh at Harvard’s Faculty of Arts and Sciences Center for Systems Biology 2013).
Behind the scenes…
Researchers have reported obese patients showing a decrease in the relative proportion of Bacteroides as compared to lean individuals. All these studies suggest that the obese state is associated with modifications in microbiota composition and that changes in microbial fermentation of dietary polyssacharides will influence intestinal absorption of monosaccharides and short-chain fatty acids — and, consequently, their conversion to more complex lipids in the liver and deposit of lipids in adipocytes. Several other proteins/systems (such as the endocannabinoid system and the tight junction protein zona occludin-1) are influenced by gut colonisation and are changed upon dietary modulation of gut microbiota composition, which are implicated in the control of inflammation, gut barrier function, gut motility, nutrient oxidation, and storage.
Written by Zakiya Sacur, BHSc. Nutr. Med., Research Nutrition Technical Consultant.